精子发生

… Spermatogenesis is a continuous process by which stem spermatogonia transform within the seminiferous tubules … can be observed in any given testicular tubule cross section. Also the …

One of the major concerns of the world health community is the infertility. The definition of infertility according to the World Health Organization (WHO) and the American Society for Reproductive Medicine (ASRM) is the inability of a healthy couple to achieve a conception after one year of regular, unprotected intercourse. Fertility complications affect seven percent of the male. The causes of infertility were divided to non-obstructive and obstructive. But, in almost 75% of male infertility cases are idiopathic with predominance of the genetic abnormalities. Numerical or structural chromosomal abnormalities are considered as genetic abnormalities that occur during the meiotic division in spermatogenesis. These abnormalities get transferred to the Offspring, which affects the normal and even the artificial conception. In the human reproduction, sperm cells are considered as a delivery vehicle for the male genetic material packed in chromosomes, which are composed of nearly 2-meter Deoxyribonucleic acid (DNA) molecule and their packaging proteins. This chapter points to grant a summarized description of individual components of the male reproductive system: the seminiferous tubule and spermatogenesis. Here, we describe step by step the structure of the testis seminiferous tubule and what occurs inside these tubules like cell communication and germ cell development from spermatogonia until spermatozoon. This book chapter is very useful for the biologists and physicians working in Assisted reproduction field to understand the physiology and pathology of spermatogenesis.

… Dark type A spermatogonia are stem cells of the seminiferous tubules that have an intensely stained dark ovoid nucleus containing fine granular chromatin. These cells divide by mitosis …

… useful criteria for dividing the cycle of the seminiferous epithelium into stages as well as … activity of spermatocytes have been used to divide the cycle of the seminiferous epithelium into …

… and direction of spermatogenic waves along the length of adult seminiferous tubules as well as the site of the first onset of spermatogenesis in postnatal seminiferous tubules. These …

… Spermatogenesis involves spermatogonia which arise from embryonic gonocytes and are located at the base of seminiferous tubules in adults. Stem cell spermatogonia divide by …

… spermatocytes. During the cell divisions and maturation associated with the transition of type A 1 spermatogonia … the luminal side of the seminiferous tubules. Subsequently, spermatids …

The aim of this study was to identify potential androgen-regulated proteins (ARP) that might mediate the supportive effects of testosterone on spermatogenesis. Adult rats were injected with ethane dimethane sulphonate (EDS) to destroy Leydig cells and thus induce complete testosterone withdrawal. Other EDS-treated rats were injected with 25 mg testosterone esters (TE) every 3 days to maintain quantitatively normal spermatogenesis. A timeframe for the study of androgen action on spermatogenesis was deduced from enumeration of degenerating germ cells at stage VII of the spermatogenic cycle in perfusion-fixed testes from rats in the early stages (4 to 8 days) after EDS treatment. Based on this data and changes in testicular interstitial fluid volume, long seminiferous tubule segments were isolated from control rats and from EDS-treated rats (+/- TE-supplementation) at stages II-V, VI-VIII, or IX-XII, 2 days to 6 days after EDS treatment. Seminiferous tubule segments were incubated for 22 hours with 60 microCi 35S-labelled methionine. Incorporation into newly synthesized proteins in the seminiferous tubule culture medium (= secreted proteins) or in seminiferous tubule lysates (= intracellular proteins) was determined by trichloroacetic acid-precipitation followed by analysis using two-dimensional sodium dodecylsulfate polyacrylamide gel electrophoresis. In control rats, incorporation of 35S-methionine into proteins secreted by isolated seminiferous tubules was more than twice as great at stages VI-VIII than at stages II-V or IX-XII. This doubling in methionine incorporation into stages VI-VIII secreted proteins was abolished, however, 4 days after EDS treatment (when germ cell degeneration at stage VII was only just evident). A similar change occurred 4 days after testosterone withdrawal induced by immunoneutralization of luteinizing hormone. In the latter case and after EDS treatment, TE-supplementation of rats from day 0 maintained the normal control pattern of methionine incorporation into seminiferous tubule secreted proteins, although 6 days after EDS and TE treatment, incorporation into stages VI-VIII secreted proteins was 19% lower (P less than 0.05) than in the control group. In contrast, incorporation of methionine into proteins secreted by seminiferous tubules at stages II-V and IX-XII was unaffected by EDS and TE pretreatment, as was incorporation into intracellular proteins at all stages.(ABSTRACT TRUNCATED AT 400 WORDS)

… Spermatogenesis is the sum total of the events … Spermatogenesis occurs within seminiferous tubules of the testis. It is a lengthy, chronological process by which stem cell spermatogonia …

The aim of the present study was to reconstruct seminiferous tubules and analyze spermatogenic waves in seminiferous epithelia in developing and adult mice using serial paraffin sections and high-performance three-dimensional (3D) reconstruction software. By labeling the basement membrane of seminiferous tubules with fluorescent immunohistochemistry or periodic acid-Schiff-hematoxylin staining, all seminiferous tubules were reconstructed in 9 testes from 9 different mice, 3 each at 0, 21 and 90 days (adult) postpartum. The 3D structure of seminiferous tubules, including the number and length of tubules as well as the number of connections with the rete testis, branching points and blind ends, was assessed accurately. Although tubules showed marked variations among individual mice, their overall structure was regular and retained from newborn to adult mice. Some seminiferous tubules contained inner portions running distant from the testis surface. In a representative testis at 21 days, the sites at which spermatids initially occurred were examined by labeling acrosomes and were found to be preferentially distributed in the upper and medial portions of the testis close to the rete testis. In a representative adult testis, 76 complete waves with an average length of 16.9 mm were found and their directions were analyzed. The methods used in the present study will be useful for investigating the structure and function of seminiferous tubules in mice and humans under normal and pathological conditions, such as infertility.

The physiological function of spermatogenesis in Caenorhabditis elegans , Drosophila melanogaster and mammals is to produce spermatozoa (1n, haploid) that contain only half of the genetic material of spermatogonia (2n, diploid). This half number of chromosomes from a spermatozoon will then be reconstituted to become a diploid cell upon fertilization with an egg, which is also haploid. Thus, genetic information from two parental individuals can be passed onto their offspring. Spermatogenesis takes place in the seminiferous epithelium of the seminiferous tubule, the functional unit of the mammalian testis. In mammals, particularly in rodents, the fascinating morphological changes that occur during spermatogenesis involving cellular differentiation and transformation, mitosis, meiosis, germ cell movement, spermiogenesis and spermiation have been well documented from the 1950s through the 1980s. During this time, however, the regulation of, as well as the biochemical and molecular mechanisms underlying these diverse cellular events occurring throughout spermatogenesis, have remained largely unexplored. In the past two decades, important advancements have been made using new biochemical, cell and molecular biology techniques to understand how different genes, proteins and signalling pathways regulate various aspects of spermatogenesis. These include studies on the differentiation of spermatogonia from gonocytes; regulation of spermatogonial stem cells; regulation of spermatogonial mitosis; regulation of meiosis, spermiogenesis and spermiation; role of hormones (e.g. oestrogens, androgens) in spermatogenesis; transcriptional regulation of spermatogenesis; regulation of apoptosis; cell–cell interactions; and the biology of junction dynamics during spermatogenesis. The impact of environmental toxicants on spermatogenesis has also become an urgent issue in the field in light of declining fertility levels in males. Many of these studies have helped investigators to understand important similarities, differences and evolutionary relationships between C. elegans , D. melanogaster and mammals relating to spermatogenesis. In this Special Issue of the Philosophical Transactions of the Royal Society B: Biological Sciences , we have covered many of these areas, and in this Introduction , we highlight the topic of spermatogenesis by examining its past, present and future.

Throughout spermatogenesis multiplication, maturation and differentiation of germ cells results in the formation of the male gamete. The understanding of spermatogenesis needs detailed informations about the organization of the germinal epithelium, the structure and function of different types of germ cells, endocrine and paracrine cells and mechanisms, intratesticular and extratesticular regulation of spermatogenesis. Normal germ cells must be discriminated from malformed, apoptotic and degenerating germ cells and tumor cells. Identification of the border line between normal and disturbed spermatogenesis substantiate the diagnosis of impaired male fertility. The profound knowledge of the complicate process of spermatogenesis and all cells or cell systems involved with is the prerequisite to develop concepts for therapy of male infertility or to handle germ cells in the management of assisted reproduction.

… regulation of spermatogenesis taking … spermatogenesis and indicates that the crucial regulatory mechanisms controlling sperm output are targeted toward differentiating spermatogonia …

Mouse spermatogenesis, from spermatogonial stem cell proliferation to sperm formation, can be reproduced in vitro by culturing testis tissue masses of neonatal mice. However, it remains to be determined whether this method is also applicable when testis tissues are further divided into tiny fragments, such as segments of the seminiferous tubule (ST), a minimal anatomical unit for spermatogenesis. In this study, we investigated this issue using the testis of an Acrosin-GFP/Histone H3.3-mCherry (Acr/H3) double-transgenic mouse and monitored the expression of GFP and mCherry as indicators of spermatogenic progression. Initially, we noticed that the cut and isolated stretches of ST shrunk rapidly and conglomerated. We therefore maintained the isolation of STs in two ways: segmental isolation without truncation or embedding in soft agarose. In both cases, GFP expression was observed by fluorescence microscopy. By whole-mount immunochemical staining, meiotic spermatocytes and round and elongating spermatids were identified as Sycp3-, crescent-form GFP-, and mCherry-positive cells, respectively. Although the efficiency was significantly lower than that with tissue mass culture, we clearly showed that spermatogenesis can be induced up to the elongating spermatid stage even when the STs were cut into short segments and cultured in isolation. In addition, we demonstrated that lowered oxygen tension was favorable for spermatogenesis both for meiotic progression and for producing elongating spermatids in isolated STs. Culturing isolated STs rather than tissue masses is advantageous for explicitly assessing the various environmental parameters that influence the progression of spermatogenesis.

… spermatogonia through a well-defined progression of mitotic expansions, meiotic reduction divisions, … focuses on the commitment of male germ cells to meiosis. The case will be made …

… of spermatogenesis but acts to optimise germ cell … spermatocytes to complete meiosis and form spermatids. Animals lacking androgen receptors fail to generate post-meiotic germ cells, …

… murine germ cell differentiation in three-… -meiotic male germ cells [revealed by the absence of meiotic marker expression (eg Boule)] obtained from immature mice pass through meiosis …

Gametogenesis in both the male and female mammal represents a specialized and highly regulated series of cell cycle events, involving both mitosis and meiosis as well as subsequent differentiation. Recent advances in our understanding of the genetic control of the eukaryotic cell cycle have underscored the evolutionarily-conserved nature of these regulatory processes. However, most of the data have been obtained from yeast model systems and mammalian cell lines. Furthermore, most of the observations focus on regulation of mitotic cell cycles. In the present paper: (i) aspects of gametogenesis in mammals that represent unique cell-cycle control points are highlighted; (ii) current knowledge on the regulation of the germ cell cycle, in the context of what is known in yeast and other model eukaryotic systems, is summarized; and (iii) strategies that can be used to identify additional cell cycle regulating genes are outlined.

Spermatogenesis is a complex and highly regulated process involving the proliferation, differ-entiation, and apoptosis of germ cells. This process is controlled by various hormonal, genetic, and environmental factors, including temperature. In Hormonal regulation, Follicle-Stimulating Hormone (FSH), Luteinizing Hormone (LH) and testosterone (T), are essential for a correct spermatogenesis development from early stages and spermatogonia proliferation to germ cells maturation. Other hormones, like inhibin and activin, finely participate tuning the process of spermatogenesis. Genetic regulation involves various transcription factors such as SOX9, SRY, and DMRT1, which are crucial for the development and maintenance of the testis and germ cells. MicroRNAs (miRNAs) play a significant role by regulating gene expression post-transcriptionally. Epigenetic modifications, including DNA methylation, histone modifica-tions, and chromatin remodelling, are also vital. Temperature regulation is another critical as-pect, with the testicular temperature maintained around 2-4°C below body temperature, essen-tial for efficient spermatogenesis. Heat shock proteins (HSPs) protect germ cells from heat-induced damage by acting as molecular chaperones, ensuring proper protein folding and preventing the aggregation of misfolded proteins during thermal stress. Elevated testicular temperature can impair spermatogenesis, increasing germ cell apoptosis, and inducing oxidative stress, DNA damage, and disruption of the blood-testis barrier, leading to germ cell death and impaired differentiation. Cellular mechanisms of germ cell proliferation, differentiation, and death include the mitotic divisions of spermatogonia to maintain the germ cell pool and pro-duce spermatocytes. Spermatocytes undergo meiosis to produce haploid spermatids, which then differentiate into mature spermatozoa. Apoptosis, or programmed cell death, ensures the re-moval of defective germ cells and regulates the germ cell population. Hormonal imbalance, ge-netic defects, and environmental stress can trigger apoptosis during spermatogenesis. Under-standing these mechanisms is crucial for addressing male infertility and developing therapeutic interventions. Advances in molecular biology and genetics continue to uncover the intricate de-tails of how spermatogenesis is regulated at multiple levels, providing new insights and poten-tial targets for treatment.

Spermatogonial stem cells (A(s) spermatogonia) are single cells that either renew themselves or produce A(pr) (paired) spermatogonia predestined to differentiate. In turn, the A(pr) divide into chains of A(al) (aligned) spermatogonia that also divide. The ratio between self-renewal and differentiation of the stem cells is regulated by glial cell line-derived neurotrophic factor produced by Sertoli cells, while the receptors are expressed in stem cells. A(s), A(pr) and A(al) spermatogonia proliferate during part of the epithelial cycle forming many A(al) spermatogonia. During epithelial stage VIII, almost all A(al) spermatogonia, few A(pr) and very few A(s) spermatogonia differentiate into A1 spermatogonia. A number of molecules are involved in this differentiation step including the stem cell factor-c-kit system, the Dazl RNA binding protein, cyclin D(2) and retinoic acid. There is no fine regulation of the density of spermatogonial stem cells and consequently, in some areas, many A1 and, in other areas, few A1 spermatogonia are formed. An equal density of spermatocytes is then obtained by the apoptosis of A2, A3 or A4 spermatogonia to remove the surplus cells. The Bcl-2 family members Bax and Bcl-x(L) are involved in this density regulation. Several mechanisms are available to cope with major or minor shortages in germ cell production. After severe cell loss, stem cell renewal is preferred above differentiation and the period of proliferation of A(s), A(pr) and A(al) spermatogonia is extended. Minor shortages are dealt with, at least in part, by less apoptosis among A2-A4 spermatogonia.

… cells preparing for division. The spermatogonia and preleptotene primary spermatocytes are the only germ cells … , a few primary spermatocytes went through meiotic divisions in the first …

Mammalian gametogenesis provides a unique system in which to study cell-cycle regulation. Furthermore, understanding the genetic program controlling the mitotic and meiotic divisions of the germ line will provide insight into understanding infertility and new directions for contraception. Male and female germ cells have stages of cell-cycle regulation in common, including a mitotic proliferative stage, entry into meiosis, completion of a reductive division, and entry into a quiescent state awaiting signals at fertilization. However, the timing of these events - and, indeed, even the stage of development at which these events occurs - differs in the two sexes. The genes involved in controlling these specialized mitotic and meiotic cycles of mammalian germ cell differentiation are only now being identified. They include a complex array of kinases, phosphatases, regulatory proteins (e.g., cyclins), and an equally complex array of substrates, including components of the nuclear and cytoplasmic structures involved in cell division. This chapter provides an overview of our current understanding of cell-cycle regulation in mammalian mitotic cells and the importance of restriction points. A summary of observations regarding the expression of various cell-cycle regulatory genes in mouse gametes is provided, along with comments on interesting differences between mitotic and meiotic cells. Finally, the role of the novel A-type cyclin, cyclin A1, during male meiosis is discussed in depth.

Spermatogenesis is the process of generation of male reproductive cells from spermatogonial stem cells in the seminiferous epithelium of the testis. During spermatogenesis, key spermatogenic events such as stem cell self-renewal and commitment to meiosis, meiotic recombination, meiotic sex chromosome inactivation, followed by cellular and chromatin remodeling of elongating spermatids occur, leading to sperm cell production. All the mentioned events are at least partially controlled by the epigenetic modifications of DNA and histones. Additionally, during embryonal development in primordial germ cells, global epigenetic reprogramming of DNA occurs. In this review, we summarized the most important epigenetic modifications in the particular stages of germ cell development, in DNA and histone proteins, starting from primordial germ cells, during embryonal development, and ending with histone-to-protamine transition during spermiogenesis. La spermatogenèse est le processus de génération de cellules reproductrices mâles à partir de cellules souches spermatogoniales, dans l’épithélium séminifère du testicule. Au cours de la spermatogenèse, des événements spermatogéniques clés tels que l’auto-renouvellement des cellules souches et l’engagement dans la méiose, la recombinaison méiotique, l’inactivation méiotique du chromosome sexuel, suivis d’un remodelage cellulaire et chromatique des spermatides allongées se produisent, conduisant à la production de spermatozoïdes. Tous les événements mentionnés sont au moins partiellement contrôlés par les modifications épigénétiques de l’ADN et des histones. De plus, au cours du développement embryonnaire, une reprogrammation épigénétique globale de l’ADN se produit dans les cellules germinales primordiales. Dans cette revue, nous avons résumé les modifications épigénétiques les plus importantes dans les étapes particulières du développement des cellules germinales, dans l’ADN et les protéines histones, en partant des cellules germinales primordiales, au cours du développement embryonnaire, jusqu’à la transition histone-protamine pendant la spermiogenèse.

… two meiotic divisions resting secondary spermatocytes show … kills spermatogonia without affecting the other germ cell … to allow preleptotene spermatocytes and early meiotic cells to …

… the successful progression of spermatogonia into spermatozoa. … have provided evidence that spermatogonia in advance stage of … the hormonal pathways regulating spermatogenesis. …

… Spermiogenesis is the process by which haploid round … Spermiogenesis begins after spermatocytes complete 2 quick … The different steps, or phases, of spermiogenesis are …

The ultrastructure of the male reproductive system of Didymocystis wedli was studied for the first time, demonstrating spermiogenesis and spermatogenesis at different cell stages. The spermatozoa morphology was compared with that of other Digenea species. It was observed that the different cells of the spermatogenesis process follow the classic pattern reported for the majority of the parasitic platyhelminthes. During spermiogenesis, rootlet fibers, electrondense bodies and median cytoplasmic process were not observed. The mature spermatozoa of D. wedli were filiform, presenting nucleus, mitochondrion and two 9+1 axonemes, with a biflagellate distal extremity.

The role of selenium in male fertility is reviewed with special emphasis on selenoprotein P and phospholipid hydroperoxide glutathione peroxidase (GPx4) in spermiogenesis. Inverse genetics reveal that selenoprotein P is required for selenium supply to the testis. GPx4 is abundantly synthesized in spermatids. As a moonlighting protein it is transformed in the later stages of spermiogenesis from an active selenoperoxidase into a structural protein that becomes a constituent of the mitochondrial sheath of spermatozoa. The transformation is paralleled by loss of glutathione. Mechanistically, the process is an alternate substrate inactivation of GPx4 resulting from reactions of its selenenic form with thiols of GPx4 itself and other proteins. Circumstantial evidence and ongoing experimental genetics indicate that the mitochondrially expressed form of the GPx4 gene is the most relevant one in spermiogenesis, with the nuclear form being dispensable for fertility and the role of cytosolic GPx4 remaining unclear. Clinical data reveal a strong association of low sperm GPx4 with infertility. Thus, impaired GPx4 biosynthesis, due to selenium deficiency or to genetic defects in gpx4 itself or in proteins involved in Se distribution and selenoprotein biosynthesis, causes male infertility, but can also be an epiphenomenon due to any perturbation of testicular function.

… on spermiation and the transition from round to elongating steps of spermiogenesis. Mid-stage meiotic spermatocytes also undergo an immediate and obvious regression. After long …

… that spermatocytes completed meiosis and spermatogenesis … , but is required for the completion of spermiogenesis. … of infertility is failure of spermiogenesis rather than sperm motility. …

In spite of the availability of abundant data about in vitro spermatogenesis in laboratory animals, studies on human in vitro spermatogenesis are scarce. This study employed a relatively simple culture system, involving all cell types of seminiferous tubules, to analyze the effects of FSH and testosterone (T) on different characteristics of human germ and Sertoli cells in culture. By using fluorescence in-situ hybridization, we show that in vitro reduction of germ cell ploidy can be stimulated by FSH but not by T. FSH, but not T, also induced unexpectedly rapid (24–48 h) morphological changes resembling spermiogenesis, although individual changes (spermatid nucleus condensation and protrusion, cell body elongation, and flagellar growth) proceeded in an uncoordinated way and mostly resulted in the development of abnormal forms of elongated spermatids. Though ineffective alone, T potentiated the effects of FSH on meiosis and spermiogenesis. These effects of T were probably caused by the prevention of Sertoli cell apoptosis, an effect that could not be mimicked by FSH. These data show that, in the presence of high concentrations of FSH and T, human spermatogenesis can proceed in vitro with an unusual speed, but the resulting gametes are morphologically abnormal. The potential practical relevance of these findings to assisted reproduction remains to be assessed.

… the spermatogenic cells by phase contrast microscopy (11). We have used this method to isolate spermatogenic … to investigate the ability of the primary spermatocytes to undergo meiotic …

… cells is silenced while the spermatogonia become sensitive to mitotic signals. Upon the initiation of spermatogenesis, the spermatogonia make contact with the … ce ss of spermiogenesis …

Spermatogenesis is a long and complex process that, despite the shared overall goal of producing the male gamete, displays striking amounts of interspecific diversity. In this review, we argue that sperm competition has been an important selection pressure acting on multiple aspects of spermatogenesis, causing variation in the number and morphology of sperm produced, and in the molecular and cellular processes by which this happens. We begin by reviewing the basic biology of spermatogenesis in some of the main animal model systems to illustrate this diversity, and then ask to what extent this variation arises from the evolutionary forces acting on spermatogenesis, most notably sperm competition. We explore five specific aspects of spermatogenesis from an evolutionary perspective, namely: (i) interspecific diversity in the number and morphology of sperm produced; (ii) the testicular organizations and stem cell systems used to produce them; (iii) the large number and high evolutionary rate of genes underpinning spermatogenesis; (iv) the repression of transcription during spermiogenesis and its link to the potential for haploid selection; and (v) the phenomenon of selection acting at the level of the germline. Overall we conclude that adopting an evolutionary perspective can shed light on many otherwise opaque features of spermatogenesis, and help to explain the diversity of ways in which males of different species perform this fundamentally important process.

… spermatogenesis in vitro, including meiosis, have remained elusive. Such procedures have the potential to facilitate (1) mechanistic studies of spermatogenesis, (… vitro spermatogenesis (…

… requirement of Six5 for both spermatogenic cell survival and spermiogenesis. Leydig cell … Thus, decreased c-Kit levels could contribute to the elevated spermatogenic cell apoptosis and …

… of spermatogonia, how germ … cycle of the seminiferous epithelium, relative frequencies of cellular associations, durations of the cycle of the seminiferous epithelium and spermatogenesis…

… Stage I of human seminiferous epithelium cycle based on morphological features of testis germ cells, from spermatogonia up to spermatids under high-resolution light microscopy. The …

… spermatogenesis begins with the transition of undifferentiated A spermatogonia to differentiating A1 spermatogonia… constitute the basis for asynchronous spermatogenesis in adults. The …

… associated spermatogenic cells. The current knowledge about the local regulation of the seminiferous epithelium at different stages of the epithelial cycle is summarized in this review. …

… in spermatogenesis, … spermatogenesis by sending signals back-and-forth between Sertoli and germ cells, in order to precisely regulate spermatogonial cell renewal by mitosis, cell cycle …

… at a given point of the tubule is called the cycle of the seminiferous epithelium. The dependence of spermatogenesis on pituitary FSH and on androgens secreted by Leydig cells in the …

… epithelium became the object of a renewed curiosity and intcrcst. From the numerous reviews on mammalian spermatogenesis … that the seminiferous epithelium of various mammals has …

… FIGURE 1 is a schematic drawing of the cross section of a seminiferous tubule at stage VII of the epithelial cycle of spermatogenesis in the rat testis, illustrating that the seminiferous …

… ’ and ‘phases’ of spermatogenesis, which progress through precisely timed and highly organized cycles. These cycles of spermatogenesis are essential for continuous sperm production…

… cells (A s spermatogonia) that divide 2–3 times per epithelial cycle and render either two … spermatogonia that differentiate during epithelial stage VIII. The organization of the epithelium …

… seminiferous epithelium cycle in goats. In the present study, the duration of spermatogenesis … The duration of each spermatogenic cycle in goats is 10.6 ± 0.5 days (SEM). Considering …

… differentiate into intermediate spermatogonia (In) and then type B spermatogonia (B) ( Figure 1C … At stage VII of the epithelial cycle, type B spermatogonia differentiate into preleptotene, …

… epithelium cycle was determined to be 10.6 ± 1.0 days and the total duration of spermatogenesis, based on 4.5 cycles, … formed from each type A1 spermatogonia. The meiotic index was …

… regulation. However, many aspects of the mechanisms regulating gene expression in spermatogenic … The final division produces preleptotene spermatocytes, which begin the meiotic …

… , meiosis of spermatocytes, and spermiogenesis, the … spermatogonia that are committed to proliferation, meiosis, and … most important hormones that regulate spermatogenesis. A typical …

… regulated by testosterone are being identified. In this review, the critical steps of spermatogenesis that are regulated … the genes found to be regulated after altering testosterone levels or …

Meiosis is essential for gamete production in all sexually reproducing organisms. It entails two successive cell divisions without DNA replication, producing haploid cells from diploid ones. This process involves complex morphological and molecular differentiation that varies across species and between sexes. Specialized genomic events like meiotic recombination and chromosome segregation are tightly regulated, including preparation for post-meiotic development. Research in model organisms, notably yeast, has shed light on the genetic and molecular aspects of meiosis and its regulation. Although mammalian meiosis research faces challenges, particularly in replicating gametogenesis in vitro, advances in genetic and genomic technologies are providing mechanistic insights. Here we review the genetics and molecular biology of meiotic gene expression control, focusing on mammals.

… patterns of transcriptional regulation underlying male meiosis and gametogenesis compared … expression throughout meiotic and postmeiotic stages of spermatogenesis because these …

… meiotic events, we focus on the essential features of meiosis. … in meiosis we consider what is known about genetic regulation … in regulating meiotic initiation in both spermatogenesis and …

Spermatogenesis is a continuous and productive process supported by the self-renewal and differentiation of spermatogonial stem cells (SSCs), which arise from undifferentiated precursors known as gonocytes and are strictly controlled in a special ‘niche’ microenvironment in the seminiferous tubules. Sertoli cells, the only somatic cell type in the tubules, directly interact with SSCs to control their proliferation and differentiation through the secretion of specific factors. Spermatocyte meiosis is another key step of spermatogenesis, which is regulated by Sertoli cells on the luminal side of the blood–testis barrier through paracrine signaling. In this review, we mainly focus on the role of Sertoli cells in the regulation of SSC self-renewal and spermatocyte meiosis, with particular emphasis on paracrine and endocrine-mediated signaling pathways. Sertoli cell growth factors, such as glial cell line-derived neurotrophic factor (GDNF) and fibroblast growth factor 2 (FGF2), as well as Sertoli cell transcription factors, such as ETS variant 5 (ERM; also known as ETV5), nociceptin, neuregulin 1 (NRG1), and androgen receptor (AR), have been identified as the most important upstream factors that regulate SSC self-renewal and spermatocyte meiosis. Other transcription factors and signaling pathways (GDNF–RET–GFRA1 signaling, FGF2–MAP2K1 signaling, CXCL12–CXCR4 signaling, CCL9–CCR1 signaling, FSH–nociceptin/OPRL1, retinoic acid/FSH–NRG/ERBB4, and AR/RB–ARID4A/ARID4B) are also addressed.

… of Mei-S332 and Ord is required for proper regulation of meiotic cohesion (3–7). Analysis of … the normal meiotic and mitotic spindle structure. Immunolocalization of Asp in spermatocytes …

Spermatogenesis is composed of three distinctive phases, which include self-renewal of spermatogonia via mitosis, spermatocytes undergoing meiosis I/II and post-meiotic development of haploid spermatids via spermiogenesis. Spermatogenesis also involves condensation of chromatin in the spermatid head before transformation of spermatids to spermatozoa. Epigenetic regulation refers to changes of heritably cellular and physiological traits not caused by modifications in the DNA sequences of the chromatin such as mutations. Major advances have been made in the epigenetic regulation of spermatogenesis. In this review, we address the roles and mechanisms of epigenetic regulators, with a focus on the role of microRNAs and DNA methylation during mitosis, meiosis and spermiogenesis. We also highlight issues that deserve attention for further investigation on the epigenetic regulation of spermatogenesis. More importantly, a thorough understanding of the epigenetic regulation in spermatogenesis will provide insightful information into the etiology of some unexplained infertility, offering new approaches for the treatment of male infertility.

… Also, during spermatogenesis a key epigenetic process termed meiotic sex chromosome inactivation (MSCI) occurs; MSCI leads to the inactivation of most genes on the X and Y …

Spermatogenesis in mammals is achieved by multiple players that pursue a common goal of generating mature spermatozoa. The developmental processes acting on male germ cells that culminate in the production of the functional spermatozoa are regulated at both the transcription and post-transcriptional levels. This review addresses recent progress towards understanding such regulatory mechanisms and identifies future challenges to be addressed in this field. We focus on transcription factors, chromatin-associated factors and RNA-binding proteins necessary for spermatogenesis and/or sperm maturation. Understanding the molecular mechanisms that govern spermatogenesis has enormous implications for new contraceptive approaches and treatments for infertility.

Abstract Oncopeltus fasciatus males fed the ancestral diet of milkweed seeds prioritize reproduction over lifespan as evidenced by higher rates of fertility and shorter lifespans than males from the same population fed the adapted diet of sunflower seeds. We examined the proximate mechanisms by which milkweed‐fed males maintained late‐life fertility. We tested the hypothesis that older milkweed‐fed males maintained fertility by producing more, higher quality sperm. Our results, that older males have more sperm, but their sperm do not have higher viability, are in general agreement with other recent studies on how nutrition affects male fertility in insects. We further examined the mechanisms by which sperm are produced by examining the progression of spermatogonial cells through the cell cycle during the transit amplification divisions. We demonstrated that diet affects the likelihood of a spermatocyst being in the S‐phase or M‐phase of the cell cycle. Given work in model systems, these results have implications for subtle effects on sperm quality either through replication stress or epigenetic markers. Thus, viability may not be the best marker for sperm quality and more work is called for on the mechanisms by which the germline and the production of sperm mediate the cost of reproduction.

Transit amplification (TA) of progenitor cells maintains tissue homeostasis by balancing proliferation and differentiation. In Drosophila testis, the germline proliferation is tightly regulated by factors present in both the germline and the neighbouring somatic cyst cells (SCCs). Although the exact mechanism is unclear, the epidermal growth factor receptor (EGFR) activation in SCCs has been reported to control spermatogonial divisions within a cyst, through downstream activations of Rac1-dependent pathways. Here, we report that somatic activation of the mitogen-activated protein kinase (Rolled/ERK) downstream of EGFR is required to synchronize the mitotic divisions and regulate the transition to meiosis. The process operates independently of the Bag-of-marble activity in the germline. Also, the integrity of the somatic cyst enclosure is inessential for this purpose. Together, these results suggest that synchronization of germ-cell divisions through somatic activation of distinct ERK-downstream targets independently regulates TA and subsequent differentiation of neighbouring germline cells.

ABSTRACT Bobby sox homolog (Bbx) is an evolutionally conserved gene, but its biological function remains elusive. Here, we characterized defects of Bbx mutant rats that were created by PiggyBac-mediated insertional mutagenesis. Smaller body size and male infertility were the two major phenotypes of homozygous Bbx mutants. Bbx expression profile analysis showed that Bbx was more highly expressed in the testis and pituitary gland than in other organs. Histology and hormonal gene expression analysis of control and Bbx-null pituitary glands showed that loss of Bbx appeared to be dispensable for pituitary histogenesis and the expression of major hormones. BBX was localized in the nuclei of postmeiotic spermatids and Sertoli cells in wild-type testes, but absent in mutant testes. An increased presence of aberrant multinuclear giant cells and apoptotic cells was observed in mutant seminiferous tubules. TUNEL-positive cells costained with CREM (round spermatid marker), but not PLZF (spermatogonia marker), gammaH2Ax (meiotic spermatocyte marker), or GATA4 (Sertoli cell marker). Finally, there were drastically reduced numbers and motility of epididymal sperm from Bbx-null rats. These results suggest that loss of BBX induces apoptosis of postmeiotic spermatids and results in spermiogenesis defects and infertility.

… no GSCs, 27% showed reduced spermatogonia with spermatocytes near the hub, and 23% … GSCs and 15% had reduced spermatogonia with spermatocytes near the hub, whereas 75…

SUMMARY Sertoli cells are supporting cells of the testicular seminiferous tubules, which provide a nurturing environment for spermatogenesis. Adult Sertoli cells are polarized so that they can simultaneously support earlier-stage spermatogenic cells (e.g., spermatogonia) basally and later-stage cells (e.g., spermatids) apically. To test the consequences of disrupting cell polarity in Sertoli cells, we perform a Sertoli-specific conditional deletion of Rac1, which encodes a Rho GTPase required for apicobasal cell polarity. Rac1 conditional knockout adults exhibit spermatogenic arrest at the round spermatid stage, with severe disruption of Sertoli cell polarity, and show increased germline and Sertoli cell apoptosis. Thus, Sertoli Rac1 function is critical for the progression of spermatogenesis but, surprisingly, is dispensable for fetal testicular development, adult maintenance of undifferentiated spermatogonia, and meiotic entry. Our data indicate that Sertoli Rac1 function is required only for certain aspects of spermatogenesis and reveal that there are distinct requirements for cell polarity during cellular differentiation.

Production of specialized cells from precursors depends on a tightly regulated sequence of proliferation and differentiation steps. In the gonad of Drosophila melanogaster, the daughters of germ line stem cells (GSC) go through precisely four rounds of transit amplification divisions to produce clusters of 16 interconnected germ line cells before entering a stereotypic differentiation cascade. Here we show that animals harbouring a transposon insertion in the center of the complex nucleoporin98-96 (nup98-96) locus had severe defects in the early steps of this developmental program, ultimately leading to germ cell loss and sterility. A phenotypic analysis indicated that flies carrying the transposon insertion, designated nup98-962288, had dramatically reduced numbers of germ line cells. In contrast to controls, mutant testes contained many solitary germ line cells that had committed to differentiation as well as abnormally small clusters of two, four or eight differentiating germ line cells. This indicates that mutant GSCs rather differentiated than self-renewed, and that these GSCs and their daughters initiated the differentiation cascade after zero, or less than four rounds of amplification divisions. This phenotype remained unaffected by hyper-activation of signalling pathways that normally result in excessive proliferation of GSCs and their daughters. Expression of wildtype nup98-96 specifically in the germ line cells of mutant animals fully restored development of the GSC lineage, demonstrating that the effect of the mutation is cell-autonomous. Nucleoporins are the structural components of the nucleopore and have also been implicated in transcriptional regulation of specific target genes. The nuclear envelopes of germ cells and general nucleocytoplasmic transport in nup98-96 mutant animals appeared normal, leading us to propose that Drosophila nup98-96 mediates the transport or transcription of targets required for the developmental timing between amplification and differentiation.

The generation of reactive oxygen species (ROS) widely occurs in metabolic reactions and affects stem cell activity by participating in stem cell self-renewal. However, the mechanisms of transit-amplifying (TA) spermatogonial divisions mediated by oxidative stress are not fully understood. Through genetic manipulation of Drosophila testes, we demonstrated that CG8005 regulated TA spermatogonial divisions and redox homeostasis. Using in vitro approaches, we showed that the knockdown of CG8005 increased ROS levels in S2 cells; the induced ROS generation was inhibited by NAC and exacerbated by H2O2 pretreatments. Furthermore, the silencing of CG8005 increased the mRNA expression of oxidation-promoting factors Keap1, GstD1, and Mal-A6 and decreased the mRNA expression of antioxidant factors cnc, Gclm, maf-S, ND-42, and ND-75. We further investigated the functions of the antioxidant factor cnc, a key factor in the Keap1-cnc signaling pathway, and showed that cnc mimicked the phenotype of CG8005 in both Drosophila testes and S2 cells. Our results indicated that CG8005, together with cnc, controlled TA spermatogonial divisions by regulating oxidative stress in Drosophila.

Abstract The foundation of mammalian spermatogenesis is provided by undifferentiated spermatogonia, which comprise of spermatogonial stem cells (SSCs) and transit-amplifying progenitors that differentiate in response to retinoic acid (RA) and are committed to enter meiosis. Our laboratory recently reported that the foundational populations of SSCs, undifferentiated progenitors, and differentiating spermatogonia are formed in the neonatal testis in part based on their differential responsiveness to RA. Here, we expand on those findings to define the extent to which RA responsiveness during steady-state spermatogenesis in the adult testis regulates the spermatogonial fate. Our results reveal that both progenitor and differentiating spermatogonia throughout the testis are capable of responding to exogenous RA, but their resulting fates were quite distinct—undifferentiated progenitors precociously differentiated and proceeded into meiosis on a normal timeline, while differentiating spermatogonia were unable to hasten their entry into meiosis. This reveals that the spermatogonia responding to RA must still complete the 8.6 day differentiation program prior to their entry into meiosis. Addition of exogenous RA enriched testes with preleptotene and pachytene spermatocytes one and two seminiferous cycles later, respectively, supporting recent clinical studies reporting increased sperm production and enhanced fertility in subfertile men on long-term RA analog treatment. Collectively, our results reveal that a well-buffered system exists within mammalian testes to regulate spermatogonial RA exposure, that exposed undifferentiated progenitors can precociously differentiate, but must complete a normal-length differentiation program prior to entering meiosis, and that daily RA treatments increased the numbers of advanced germ cells by directing undifferentiated progenitors to continuously differentiate. Summary Sentence Retinoic acid induces widespread precocity of progenitors, not differentiating spermatogonia, through steady-state spermatogenesis Graphical Abstract

The dynamic process of Drosophila spermatogenesis involves asymmetric division, mitosis, and meiosis, which ultimately results in the production of mature spermatozoa. Disorders of spermatogenesis can lead to infertility in males. ADAR (adenosine deaminase acting on RNA) mutations in Drosophila cause male infertility, yet the causative factors remain unclear. In this study, immunofluorescence staining was employed to visualize endogenous ADAR proteins and assess protein levels via fluorescence-intensity analysis. In addition, the early differentiation disorders and homeostatic alterations during early spermatogenesis in the testes were examined through quantification of transit-amplifying region length, counting the number of GSCs (germline stem cells), and fertility experiments. Our findings suggest that deletion of ADAR causes testicular tip transit-amplifying cells to accumulate and become infertile in older male Drosophila. By overexpressing ADAR in early germline cells, male infertility can be partially rescued. Transcriptome analysis showed that ADAR maintained early spermatogenesis homeostasis through the bone-morphogenetic-protein (BMP) signaling pathway. Taken together, these findings have the potential to help explore the role of ADAR in early spermatogenesis.

… The degree of stemness exhibited by different types of undifferentiated spermatogonia, the significance of transit amplification and the identity of intratesticular growth factors that govern …

… of spermatogenesis are the … transit amplifying progenitor pools. Self-renewing divisions of SSCs maintain a reservoir from which progenitor spermatogonia arise that transiently amplify …

During spermatogenesis, preleptotene spermatocytes traverse the blood–testis barrier (BTB) in the seminiferous epithelium, which is reminiscent of viral pathogens breaking through the tight junctions of host epithelial cells. The process also closely resembles the migration of leukocytes across endothelial tight junctions to reach inflammation sites. Cell adhesion molecules of the immunoglobulin superfamily (e.g., JAM/CAR/nectin) participate in germ cell migration by conferring transient adhesion between Sertoli and germ cells through homophilic and heterophilic interactions. The same molecules also comprise the junctional complexes at the BTB. Interestingly, JAM/CAR/nectin molecules mediate virus uptake and leukocyte transmigration in strikingly similar manners. It is likely that the strategy used by viruses and leukocytes to break through junctional barriers is used by germ cells to open up the inter–Sertoli cell junctions. In associating these diverse cellular events, we highlight the “guiding” role of JAM/CAR/nectin molecules for germ cell passage. Knowledge on viral invasion and leukocyte transmigration has also shed insights into germ cell movement during spermatogenesis.

… Spermatogenesis takes place in the seminiferous epithelium … cells, such as preleptotene and leptotene spermatocytes, residing in the basal compartment of the seminiferous epithelium …

Spermatogenesis is the process by … epithelial cycle were first described, reproductive biologists have been in pursuit of one question: How can a spermatogonium traverse the epithelium…

BackgroundSpermatogenesis is a complex process involving the self-renewal and differentiation of spermatogonia into mature spermatids in the seminiferous tubules. During spermatogenesis, germ cells migrate from the basement membrane to cross the blood-testis barrier (BTB) and finally reach the luminal side of the seminiferous epithelium. However, the mechanism for regulating the migration of germ cells remains unclear. In this study, we focused on the expression and function of transcriptional factor EB (TFEB), a master regulator of lysosomal biogenesis, autophagy and endocytosis, in spermatogenesis.MethodsThe expression pattern of the TFEB in mouse testes were investigated by Western blotting and immunohistochemistry analyses. Either undifferentiated spermatogonia or differentiating spermatogonia were isolated from testes using magnetic-activated cell sorting based on specific cell surface markers. Differentiation of spermatogonia was induced with 100 nM retinoic acid (RA). shRNA was used to knock down TFEB in cells. TFEB expression was detected by immunofluorescence, qRT-PCR, and Western blotting. Cell migration was determined by both transwell migration assay and wound healing assay applied to a cell line of immortalized spermatogonia, GC-1 cells.ResultsDuring testicular development, TFEB expression was rapidly increased in the testes at the period of 7 days post-partum (dpp) to 14 dpp, whereas in adult testis, it was predominantly localized in the nucleus of spermatogonia at stages VI to VIII of the seminiferous epithelial cycle. Accordingly, TFEB was observed to be mainly expressed in differentiating spermatogonia and was activated for nuclear translocation by RA treatment. Moreover, knockdown of TFEB expression by RNAi did not affect spermatogonial differentiation, but significantly reduced cell migration in GC-1 cells.ConclusionThese findings imply that regionally distinct expression and activation of TFEB was strongly associated with RA signaling, and therefore may promote cell migration across the BTB and transport along the seminiferous epithelium.

… migrating spermatocytes are bounded both apically and basally by SCTJs suggests that the basal surface of the Sertoli cells form new Sertoli-Sertoli cell … of the seminiferous epithelium …

… epithelial cycle. Herein, we briefly review some new findings in the field regarding germ cell transport in the seminiferous epithelium … cell migration across the seminiferous epithelium …

CD147, also named basigin (Bsg) or extracellular matrix (ECM) metalloproteinase inducer (EMMPRIN), is a highly glycosylated protein first identified as a tumor cell surface molecule. In cancer, it is well established that CD147 promotes metastasis by stimulating the production of MMPs. Recent studies have also suggested that it may be associated with tumor growth and angiogenesis. Interestingly, CD147 is expressed in germ cells of different development stages in the testis and its knockout mice are infertile, indicating an essential role of CD147 in spermatogenesis. While the detailed involvement of CD147 in spermatogenesis remains elusive, our recent findings have revealed a dual role of CD147 in germ cell development. On the one hand, it regulates the migration of spermatogonia and spermatocytes via the induction of MMP-2 production; on the other hand, it specifically regulates the survival/apoptosis of spermatocytes but not spermatogonia through a p53-independent pathway. In this review, we aim to provide an overview on the functions of CD147, comparing its roles in cancer and the testis, thereby providing new insights into the regulatory mechanisms underlying the process of spermatogenesis.

The functions of Sertoli cells in spermatogenesis have attracted much more attention recently. Normal spermatogenesis depends on Sertoli cells, mainly due to their influence on nutrient supply, maintenance of cell junctions, and support for germ cells’ mitosis and meiosis. Accumulating evidence in the past decade has highlighted the dominant functions of the MAPK, AMPK, and TGF-β/Smad signaling pathways during spermatogenesis. Among these pathways, the MAPK signaling pathway regulates dynamics of tight junctions and adherens junctions, proliferation and meiosis of germ cells, proliferation and lactate production of Sertoli cells; the AMPK and the TGF-β/Smad signaling pathways both affect dynamics of tight junctions and adherens junctions, as well as the proliferation of Sertoli cells. The AMPK signaling pathway also regulates lactate supply. These signaling pathways combine to form a complex regulatory network for spermatogenesis. In testicular tumors or infertile patients, the activities of these signaling pathways in Sertoli cells are abnormal. Clarifying the mechanisms of signaling pathways in Sertoli cells on spermatogenesis provides new insights into the physiological functions of Sertoli cells in male reproduction, and also serves as a pre-requisite to identify potential therapeutic targets in abnormal spermatogenesis including testicular tumor and male infertility.

… seminiferous epithelium into basal and apical (or adluminal) compartments, and is pivotal to spermatogenesis… restructuring to facilitate germ‐cell migration is regulated by two cytokines, …

… numbers, and new studies indicate that adult Sertoli cells can be made to re-enter mitotic … cells in regulation of spermatogenesis and methods for estimating the number of Sertoli cells, …

… Similar studies were conducted in vivo and in vitro to evaluate neural crest cell migration elicited by … of spermatogenic cells at any moment In a given site of the seminiferous epithelium. …

… area of the tubule” (1). Cross-sectioned seminiferous tubules contain multiple germ cell types that … The organization of these germ cells within the seminiferous tubules has been studied …

… germ cells are characteristically seen in live cells in vitro and in those cells observed in the fixed seminiferous tubules. … of the identity of individual germ cells seen in vitro and provides a …

… seminiferous tubules, and every given cross-section of the … and characterize mouse male germ cells at specific steps of … visualization of staged living spermatogenic cells in reproductive …

… Seminiferous tubule architecture, germ cell maturation steps … The germ cell maturation steps characteristic of the six cellular … The resulting atypical cell associations complicate staging of …

Abstract Spermatogenesis is a complex differentiation process that takes place in the seminiferous tubules. A specific organization of spermatogenic cells within the seminiferous epithelium enables a synchronous progress of germ cells at certain steps of differentiation on the spermatogenic pathway. This can be observed in testis cross-sections where seminiferous tubules can be classified into distinct stages of constant cellular composition (12 stages in the mouse). For a detailed analysis of spermatogenesis, these stages have to be individually observed from testis cross-sections. However, the recognition of stages requires special training and expertise. Furthermore, the manual scoring is laborious considering the high number of tubule cross-sections that have to be analyzed. To facilitate the analysis of spermatogenesis, we have developed a convolutional deep neural network-based approach named “STAGETOOL.” STAGETOOL analyses histological images of 4′,6-diamidine-2′-phenylindole dihydrochloride (DAPI)-stained mouse testis cross-sections at ×400 magnification, and very accurately classifies tubule cross-sections into 5 stage classes and cells into 9 categories. STAGETOOL classification accuracy for stage classes of seminiferous tubules of a whole-testis cross-section is 99.1%. For cellular level analysis the F1 score for 9 seminiferous epithelial cell types ranges from 0.80 to 0.98. Furthermore, we show that STAGETOOL can be applied for the analysis of knockout mouse models with spermatogenic defects, as well as for automated profiling of protein expression patterns. STAGETOOL is the first fluorescent labeling–based automated method for mouse testis histological analysis that enables both stage and cell-type recognition. While STAGETOOL qualitatively parallels an experienced human histologist, it outperforms humans time-wise, therefore representing a major advancement in male reproductive biology research.