Spermatogenesis

Spermatogenesis is an ongoing differentiation procedure that occurs in the seminiferous epithelium in the testis in males to produce spermatozoa (sperm) and is sustained by a tissue-specific stem prison cell termed the "spermatogonial stalk cell."

From: Encyclopedia of Reproduction (2d Edition) , 2018

Testicular Disorders

Shlomo Melmed MB ChB, MACP , in Williams Textbook of Endocrinology , 2020

Maintenance of Spermatogenesis

In men with prepubertal gonadotropin deficiency (e.1000., CHH), one time spermatogenesis has been initiated with LH (hCG) and FSH handling, sperm product may be maintained with LH treatment alone without continued FSH administration. 79 However, spermatogenesis is not stimulated by administration of FSH in combination with testosterone (that maintains normal concentrations of serum testosterone but with continued low LH and intratesticular testosterone concentrations) in men with CHH. Spermatogenesis may be reinitiated with LH (hCG) alone in previously gonadotropin-treated men with CHH later on a period of gonadotropin deficiency associated with exogenous testosterone replacement therapy. Furthermore, in men with gonadotropin deficiency and azoospermia acquired as an developed (e.one thousand., secondary to a pituitary adenoma), spermatogenesis may be reinitiated and maintained with LH (hCG) treatment alone. 79

In normal men with experimental gonadotropin deficiency induced past high-dose testosterone administration, spermatogenesis may be reinitiated and maintained by either LH or hCG solitary, despite markedly suppressed FSH concentrations, or by FSH alone, despite severely suppressed LH (and presumably low intratesticular testosterone) concentrations. However, sperm production was non stimulated by either LH or FSH alone to the baseline concentrations that existed earlier experimental gonadotropin suppression. 87 In this model of gonadotropin deficiency, treatment with both LH (hCG) and FSH restored sperm counts fully to baseline values. Finally, in support of the ability of FSH solitary to stimulate sperm production, spermatogenesis was maintained despite undetectable serum gonadotropin concentrations in a hypophysectomized human who had an activating FSH receptor mutation. 88

Together, these findings suggest that a normal concentration of either FSH or LH is sufficient for maintenance of qualitatively normal sperm product, but both gonadotropins are necessary for quantitatively normal spermatogenesis in male humans.

The effect of gonadotropins on specific stages of spermatogenesis has been studied in normal men with experimental gonadotropin suppression induced by the assistants of high-dose progestin and testosterone. In these gonadotropin-scarce men, selective replacement of either FSH or LH (increasing intratesticular testosterone) supported all stages of spermatogenesis, including spermatogonial maturation, meiosis, spermiogenesis, and spermiation, but each agent had predominant actions on specific stages. 89 FSH exerted a relatively greater effect on maturation of spermatogonia (conversion of spermatogonia Ap to spermatogonia B), early meiosis, and maintenance of pachytene spermatocytes (conversion of spermatogonia to pachytene spermatocytes). LH (stimulating intratesticular testosterone) had predominant effects on the completion of meiosis (conversion of pachytene spermatocytes to circular spermatids) and on spermiation (release of mature spermatozoa). LH and FSH (intratesticular testosterone) exert similar effects on spermiogenesis (conversion of round to elongated spermatids).

Reproduction and Development

R. Renkawitz-Pohl , ... M.A. Schäfer , in Comprehensive Molecular Insect Science, 2005

1.four.1 Introduction

Spermatogenesis is a highly specialized process of cellular differentiation resulting in the formation of functional spermatozoa for successful reproduction. In principle, the process of spermatogenesis is well conserved in all sexually proliferating organisms, although the size and shape of the mature sperm vary considerably among different species. Many details are comparable between mammals and Drosophila making the fly a very practiced model system to written report fertility defects. Drosophila germ cells, similar those of mammals, are set aside early in embryonic development and migrate through the primordium of the hindgut into the interior of the embryo where they bring together the somatic parts of the embryonic gonads (review: Zhao and Garbers, 2002). At the stop of the third larval instar and the onset of pupariation, the start germ cells enter meiosis (Figure 1).

Figure one. Stages of spermatogenesis in testes of belatedly third instar larvae and adult males. (a) Testis anlage of a larva showing the hub and stem cell region at the noon (asterisk), a cyst with spermatogonia (white arrow), and a cyst with main spermatocytes (black arrowhead). (b) Testis of an adult male showing the apical tip with hub and stalk cells (asterisk), spermatogonia (white arrow), spermatocytes (arrowhead), and elongated spermatids (black arrow). (c) The cyst shows synchronous meiotic divisions. (d) The left cyst shows a Nebenkern stage shortly subsequently the 2d meiotic division. In the stage dissimilarity optics the nucleus (due north) appears lite, the Nebenkern (nk) dark. The right cyst contains immature spermatids with a circular nucleus (northward) and an elongating flagellum (F). (e) β1-LacZ reporter gene expression in the male reproductive tract (Wβ1K-conveying transgenic line; Buttgereit and Renkawitz-Pohl, 1993). Within the testes (T), stalk cells and spermatogonia express β-galactosidase. In addition, β-galactosidase expression is too observed in the vas deferens (V), in accompaniment glands (G), and in the ejaculatory duct (AD). (f) β2-LacZ reporter factor expression in the male reproductive tract (Michiels et al., 1989).

Spermatogenesis is a continuous process during adult life and, thus, the adult testes comprise all stages from stem cells to mature sperm (Effigy 1). As in mammals, the germ cells develop in close contact with somatic cells, in this case the cyst cells, which are of mesodermal origin. At the very tip of the testis tube, the and so-called hub is formed by somatic support cells (asterisk in Figure 1) to which the germline stem cells (GSCs) and the cyst cell progenitors (somatic stem cells, SSCs) are physically connected. In close contact to the hub, both stem cell types divide asymmetrically depending on the JAK-STAT signaling pathway (run across Section 1.iv.3.1 for details). Ane daughter cell remains connected to the hub and maintains stalk cell characteristics. The other daughter cell becomes asunder from the hub and enters the differentiation process. This germ cell, now called spermatogonium, is surrounded past two cyst cells, thus forming a cyst in which the germ cell undergoes four mitotic divisions, meiosis, and sperm morphogenesis until individualization (see Figure 3 for an overview).

The ultrastructure and cytology of Drosophila melanogaster spermatogenesis has been extensively reviewed past Fuller (1993). This complex differentiation process from circular cells to the highly specialized structure of spermatozoa is controlled past a large number of genes (upwards to 1500) affecting spermatogenesis, which is reflected in the large number of male person sterile mutants (reviews: Lindsley and Tokuyasu, 1980; Hackstein et al., 2000). The focus here is on the recent advances in understanding the molecular ground for the dramatic changes in jail cell morphology during germ prison cell development starting with the asymmetric division of stem cells into a stem cell and a spermatogonium as the entry point to germ cell differentiation. Control of mitotic proliferation and entry into meiosis are discussed and various aspects of sperm morphogenesis highlighted, such as the formation of the axoneme and the mitochondrial derivative, the Nebenkern. Then the importance of jail cell interactions during the process is discussed (Effigy four), and finally transcriptional and translational command mechanisms during meiotic prophase, and their relevance for sperm morphogenesis (Figure three).

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Physiology and Disorders of Puberty

Shlomo Melmed MB ChB, MACP , in Williams Textbook of Endocrinology , 2020

Spermatogenesis

The first histologic evidence of spermatogenesis appears between ages 11 and 15 years ( Fig. 26.13; likewise come acrossFigs. 26.half-dozen and 26.ix). Spermaturia may exist the first sign of pubertal evolution, but the presence of sperm in urine is intermittent and therefore not a reliable indicator in all boys. Spermaturia is more prevalent in early on puberty than in late puberty, suggesting that there may exist a continuous flow of sperm through the urethra in early on puberty but that ejaculation is necessary for sperm to appear in the urine in late puberty. Spermaturia in the first-morning urine specimen occurs at a mean chronologic age of 13.3 years and at a mean pubic hair stage two to 3 in one study (or xvi years in another study), but may be found in normal boys with bilateral testicular volumes of only 3 mL and no signs of puberty. 139 Normospermia (i.e., normal sperm concentration, morphologic appearance, and move) is not present until a bone age of 17 years. The first conscious ejaculation occurs at a mean chronologic historic period of xiii.5 years in normal boys and at a hateful bone age of thirteen.v years in boys with delayed puberty. 140 The historic period of the get-go ejaculation, spermarche, decreased in China between 1995 and 2010, and a college BMI led to an earlier age of spermarche; this pattern mirrors to a degree the secular trend of menarche in girls. 141,142

The potential for fertility is reached before an adult phenotype is attained, earlier adult plasma testosterone concentrations are reached, and before PHV occurs.

Book Two

David M. de Kretser , ... Moira O'Bryan , in Endocrinology: Adult and Pediatric (7th Edition), 2016

Seminiferous Tubules

Spermatogenesis takes place within the seminiferous tubules, which, in humans, are ~200 μm in diameter and have a total length of ~600 meters occupying ~threescore% of the testis volume ( Fig. 136-1).

The terminal ends of the seminiferous tubules in the mediastinum empty via straight tubular extensions termed tubuli recti. Depending on the species, private seminiferous tubules may be highly convoluted (e.g., human), or they may form numerous relatively linear segments linked by cranial and caudal hairpin turns (e.g., rodent testes). 3

Within the epithelium of the seminiferous tubules, germ cells undergo spermatogenesis, which commences with the spermatogonia that lie adjacent to the basement membrane of the tubules and separate by mitosis. Spermatogonia, every bit well every bit renewing themselves, give ascent to cells that lose contact with the basement membrane and commence the process of meiosis, now called main spermatocytes. Having completed the start meiotic division, these cells give rise to daughter cells called secondary spermatocytes, which divide to complete meiosis to form round spermatids.

The round spermatids do not separate but undergo a circuitous metamorphosis, called spermiogenesis, to get spermatozoa that are released into the lumen of the seminiferous tubule by a procedure called spermiation.

Interspersed between the germ cells within the seminiferous epithelium are the supporting cells, chosen Sertoli cells, which extend from the basement membrane of the tubule to the lumen like a tree with its trunk abutting on the basement membrane and its branches beingness interspersed betwixt the germ cells. The physical relationship between the nondividing Sertoli cells in the developed testis and the various types of dividing and differentiating germ cells is hard to appreciate by light microscopy since the Sertoli cell cytoplasmic extensions between the germ cells are thin. The complexities of this association have, however, been thoroughly described in ultrastructural studies (run across reviews elsewhere 4,5 ) to reveal a dynamic convoluted compages. As germ cells progress through spermatogenesis, they are progressively moved apically through the seminiferous epithelium separated by processes of Sertoli prison cell cytoplasm that create pockets, or recesses between the Sertoli cells. The most mature germ cells, the spermatozoa, are ultimately released into the lumen of the seminiferous tubule (Figs. 136-2, 136-3, and 136-four).

Where adjacent Sertoli cells interface with each other higher up the basal spermatogonia, a specialized tight cell junction is formed preventing intercellular transport of substances, thus creating basal and adluminal compartments of the seminiferous tubules. These tight junctions finer form the claret-testis barrier, which can open to enable spermatogonia to lose their connectedness with the basement membrane and enter the adluminal compartment.

The sperm and luminal fluid are moved by irregular contractions of the peritubular myoid cells that lie on the external surface of the tubules through the mediastinum into the rete testis. The rete testis is a maze of anastomosing spaces within the mediastinum and drains into the epididymis. The morphology of the rete is species-specific, 6 simply can more often than not exist divided into 3 primary zones. The septal rete is composed of direct tubules that empty into the mediastinal rete, a network of anastomosing channels. These, in plough, drain into the extratesticular rete, which is characterized by wider spaces in continuity with the 6 to 12 fine efferent ductules leading to the head of the epididymis.

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Male person Reproductive Physiology

Alan W. Partin Dr., PhD , in Campbell-Walsh-Wein Urology , 2021

Spermatogenesis

Spermatogenesis is a remarkably complex and specialized process of Dna reduction and germ cell metamorphosis. Older studies accept estimated that the entire procedure in humans requires approximately 64 days ( Clermont, 1972). However, an in vivo kinetic written report in good for you men revealed thatthe total fourth dimension to produce an ejaculated sperm ranges from 42 to 76 days, suggesting that the duration of spermatogenesis tin can vary widely among individuals (Misell et al., 2006;Fig. 64.xiii).Spermatogenesis involves (1) a proliferative phase as spermatogonia divide to supervene upon their number (cocky-renewal) or differentiate into daughter cells that become mature gametes; (2)a meiotic phase when germ cells undergo a reduction division, resulting in haploid (half the normal Deoxyribonucleic acid complement) spermatids; and (iii)a spermiogenesis phase in which spermatids undergo a profound metamorphosis to become mature spermatozoa. (For fantabulous reviews, run acrossSteinberger [1976] andde Kretser and Kerr [1988].)

Abicycle of spermatogenesis involves the segmentation of primitive spermatogonial stem cells into subsequent germ cells. Several cycles of spermatogenesis coexist inside the germinal epithelium, and they are described morphologically equallystages. If spermatogenesis is viewed from a single fixed betoken within a seminiferous tubule, 6 recognizable cellular associations or stages are predictably observed in humans (Heller and Clermont, 1964) (seeFig. 64.xi). In addition, there is also a specific system of spermatogenic cycles within the tubular space, termedspermatogenic waves. The all-time bear witness suggests that human spermatogenesis exists in a spiral or helical cellular arrangement that ensures sperm production is a continuous and not a pulsatile process (Schulze, 1989;Fig. 64.xiv).

Testis Stem Cell Migration, Renewal, and Proliferation

Testis Stem Prison cell Migration

During early prenatal development,primordial germ cells migrate to the gonadal ridge and associate with Sertoli cells to grade archaic testicular cords (Witschi, 1948). These primitive germline stem cells are termedgonocytes after the gonad differentiates into a testis past forming seminiferous cords. They are chosenspermatogonia after migration to the periphery of the tubule (Gondos and Hobel, 1971).These early migrating germ cells take properties similar to embryonic stem cells and are probable the source of developed germ cell tumors (Ezeh et al., 2005). The failure of germ cells to migrate into the primitive testicle is likewise thought to be a cause ofextragonadal germ cells tumors and developed infertility resulting fromazoospermia with Sertoli jail cell–only testicular histology (Nikolic et al., 2016).

Human Male Spermatogenesis

Laurence A. Cole , in Biology of Life, 2016

Endocrine Control of Spermatogenesis

Spermatogenesis begins at puberty, when testosterone levels rise. Testosterone is critical to spermatogenesis. In the lack of testosterone, spermatogenesis only proceeds as far as the prophase 1-leptotene stage of meiosis ( Fig. 18.3). Hypophysectomy or removal of the pituitary gland leads to an absence of luteinizing hormone (LH). With the absence of LH, Leydig cells stop producing testosterone and spermatogenesis comes to a halt. In this respect, LH is as disquisitional to spermatogenesis as testosterone.

The role of follicle stimulating hormone (FSH) in men is less sure. FSH promotes growth of testosterone receptors on Sertoli cells and seminiferous tubules, this is of import. Information with rodents advises that FSH binding Sertoli cells increases the number of spermatogonia or resting spermatocytes formed prior to meiosis. Basically, LH and testosterone are disquisitional to spermatogenesis in men, but the role of FSH is secondary and less disquisitional.

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Anatomy and physiology of the reproductive system

Irina Szmelskyj DipAc MSc MBAcC , ... Alan O. Szmelskyj Do MSc AdvDipClinHyp FRSPH , in Acupuncture for IVF and Assisted Reproduction, 2015

Spermatogenesis and spermiogenesis

Spermatogenesis is the process of spermatozoa (sperm) formation. 12 Spermatogenesis starts at puberty, when the Leydig cells in the testes first to produce androgens under the influence of the Follicle-Stimulating Hormone (FSH) and the Luteinizing Hormone (LH), which are in plow controlled by the Gonadotrophin-Releasing Hormone (GnRH) produced by the hypothalamus. iii In the absence of LH and FSH, androgen levels drib, and spermatogenesis stops. 12

Spermatogenesis begins with spermatogonia (the diploid (twon) immature sperm cells derived from embryonic germ cells) dividing past mitosis. iii During their prolonged meiotic phase, the spermatocytes are sensitive to damage. 13 Some of the spermatogonia develop into primary spermatocytes.

At puberty, at that place is an increment in testosterone levels; this initiates meiosis I. During this stage, a principal spermatocyte generates two secondary spermatocytes, which then undergo meiosis II. Two haploid spermatids (haploid cells) are generated past each secondary spermatocyte, resulting in a total of four spermatids. Spermiogenesis is the last phase of spermatogenesis, and, during this phase, spermatids mature into spermatozoa (sperm cells) (Figure 2.5). 3

The spermiogenesis stage is completed with maturation of a spermatozoon. 12 Spermatogenesis takes 65–75 days three and takes identify simultaneously at different times in dissimilar regions of the testis for an fifty-fifty production and availability of mature sperm.

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Sperm Physiology and Assessment of Spermatogenesis Kinetics In Vivo

Sandro C. Esteves Md, PhD , Ricardo Miyaoska Physician, PhD , in Handbook of Fertility, 2015

Conclusions

Spermatogenesis is a highly organized and complex sequence of differentiation events that yields genetically distinct male person gametes for fertilization. Sperm product is a continuous process, initiated at puberty and continuing throughout life, which occurs in the seminiferous tubules within an immune privileged site. Spermatozoa released from the seminiferous tubules into the epididymis undergo mail-testicular maturation. Before fertilization can occur, spermatozoa must undergo further biochemical changes via capacitation and acrosome reaction, both of which occur after ejaculation. Contempo knowledge originated from a novel direct measurement of human spermatogenesis kinetics in vivo indicates that the entire sperm production procedure is shorter than previously believed. Based on this new method involving a stable isotope labeling with enriched heavy h2o and analysis of DNA isotopic enrichment in ejaculated sperm by gas chromatography/mass spectrometry, it has been besides suggested that there is a large individual biological variability in the duration of spermatogenesis. This method may go a novel tool for characterizing the relationship between spermatogenesis and semen quality in male infertility, including the measurement of the effects of gonadotoxic exposure as well as medical and surgical interventions.

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Hormonal Control of Reproductionin the Male

H. Maurice Goodman , in Bones Medical Endocrinology (Fourth Edition), 2009

Leydig Cells and Seminiferous Tubules

The two principal functions of the testis, sperm product and steroid hormone synthesis, are carried out in morphologically distinct compartments. Sperm are formed and develop within seminiferous tubules, which comprise the bulk of testicular mass. Testosterone is produced past the interstitial cells of Leydig, which lie in clusters betwixt the seminiferous tubules (Figure 12.1). The entire testis is encased in an inelastic fibrous capsule consisting of three layers of dense connective tissue and some smooth muscle.

Effigy 12.1. Histological department of human testis. The transected tubules show various stages of spermatogenesis. (From di Fiore, M.Southward.H. (1981) Atlas of Human being Histology, fifth ed., 209. Lea & Febiger, Philadelphia.)

Blood reaches the testes primarily through paired spermatic arteries and beginning is cooled past heat exchange with returning venous blood in the pampiniform plexus. This circuitous tangle of blood vessels is formed past highly tortuous and convoluted venules that environment and come up in shut apposition to the spermatic artery earlier converging to form the spermatic vein. This system provides a large surface area for warm arterial blood to transfer heat to cooler venous blood across thin vascular walls. Rewarmed venous blood returns to the systemic apportionment primarily through the internal spermatic veins.

Leydig cells are embedded in loose connective tissue that fills the spaces between semi-niferous tubules. They are big polyhedral cells with an extensive smooth endoplasmic reticulum characteristic of steroid-secreting cells. Although extensive at nativity, Leydig cells well-nigh disappear subsequently the get-go vi months of postnatal life, simply to reappear more than a decade later with the onset of puberty. In the adult, Leydig cells comprise x to 20% of testicular mass.

Seminiferous tubules are highly convoluted loops that range from about 120 to 300 µm in diameter and from 30 to lxx   cm in length. They are arranged in lobules divisional by fibrous connective tissue. Each testis has hundreds of such tubules that are connected at both ends to the rete testis (Figure 12.ii). It has been estimated that, if laid finish to end, the seminiferous tubules of the human testis would extend more than 500 meters. The seminiferous epithelium that lines the tubules consists of three cell types: spermatogonia, which are stem cells; spermatocytes which are in the process of becoming sperm; and Sertoli cells, which nurture developing sperm and secrete a variety of products into the blood and the lumina of seminiferous tubules. Seminiferous tubules are surrounded by a several layers of peritubular myoid-epithelial cells, which are contractile and assist propel the nonmotile sperm through the tubules toward the rete testis.

Figure 12.2. Diagrammatic representation of the human being testicular tubules. (From Netter, F.H. (1997) Atlas of Homo Anatomy, 2d edition, plate 362. Novartis, Eastward Hanover.)

Spermatogenesis goes on continuously from puberty to senescence forth the entire length of the seminiferous tubules. Though a continuous procedure, spermatogenesis can exist divided into three detached phases:

one

Mitotic divisions, which maintain a stem cell population of spermatogonia and provide the cells destined to become mature sperm.

2

Meiotic divisions, which reduce the chromosome number and produce a cluster of haploid spermatids.

three

Transformation of spermatids into mature spermatozoa (spermiogenesis), a process involving the loss of virtually of the cytoplasm and the development of flagella (Figure 12.iii).

Figure 12.three. The germination of mammalian germ cells. Each chief spermatogonium ultimately gives rising to 64 sperm cells. Cytokinesis is incomplete in all but the primeval spermatogonial divisions, resulting in expanding clones of germ cells that remain joined by intercellular bridges. Maturing spermatids are closely associated with and enfolded past the Sertoli cells.

The fully formed spermatozoa are then released into the tubular lumina (spermiation). These events occur forth thelength of the seminiferous tubules in a definite temporal and spatial design. A spermatogenic bike includes all the transformations from spermatogonium to spermatozoan and requires about 64 days. As the bike progresses, germ cells move from the basal portion of the germinal epithelium toward the lumen. Successive cycles begin before the previous one has been completed, so that different stages of the bicycle are seen at any given point along a tubule at dissimilar depths of the epithelium. Spermatogenic cycles are synchronized in adjacent groups of cells, but the cycles are slightly advanced in like groups of cells located immediately upstream, so that cells at whatsoever given stage of the spermatogenic cycle are spaced at regular intervals along the length of the tubules.

This circuitous series of events ensures that mature spermatozoa are produced continuously. Most 2 million spermatogonia, each giving ascent to 64 sperm cells, begin this process in each testis every day. More than 200 one thousand thousand spermatozoa are thus produced daily, or virtually half dozen 3 x14 in the half-dozen or more decades of reproductive life.

Sertoli cells are remarkable polyfunctional cells whose activities are intimately related to many aspects of the formation and maturation of spermatozoa. They extend through the entire thickness of the germinal epithelium from basement membrane to lumen and in the adult have on exceedingly irregular shapes adamant past the irresolute conformations of the 10 to 12 developing sperm cells embedded in their cytoplasm (Effigy 12.iv). Differentiating sperm cells are isolated from the bloodstream and interstitial fluid, and must rely on Sertoli cells for their sustenance. Adjacent Sertoli cells arch higher up the clusters of spermatogonia that nestle betwixt them at the level of the basement membrane. A series of tight junctions binds each Sertoli cell to the six adjacent Sertoli cells and limits passage of physiologically relevant molecules into or out of seminiferous tubules.

Figure 12.four. Ultrastructure of the Sertoli prison cell and its relation to the germ cells. The spermatocytes and early spermatids occupy niches in the sides of the columnar supporting prison cell, whereas late spermatids reside in deep recesses in its apex. (From Fawcett, D.W. (1986) A Textbook of Histology, 11th ed., 834. W.B. Saunders, Philadelphia.)

This so-called blood–testis barrier really has selective permeability that allows rapid entry of testosterone, for example, simply virtually completely excludes cholesterol. The physiological significance of the claret–testis barrier has not been established, but it is probably of some importance that spermatogonia are located on the blood side of the barrier, whereas developing spermatids are restricted to the luminal side. In addition to harboring and nurturing developing sperm, Sertoli cells secrete the watery fluid that transports spermatozoa through the seminiferous tubules and into the epididymis, where 99% of the fluid is reabsorbed. Sertoli cells also take upwardly and degrade the residuum bodies of cytoplasm shed past the developing spermatocytes.

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Roles of Small-scale Ubiquitin-Related Modifiers in Male Reproductive Part

Margarita Vigodner , in International Review of Cell and Molecular Biology, 2011

Abstract

Spermatogenesis consists of the mitotic segmentation of spermatogonia, meiosis of spermatocytes, and postmeiotic differentiation of spermatids, processes tightly controlled by hormones and growth factors secreted by testicular somatic cells. The events during spermatogenesis are precisely regulated by the sequential appearance of different proteins and their posttranslational modifications. Sumoylation (covalent modification by small ubiquitin-similar modifiers; SUMO proteins) has emerged as an important regulatory mechanism in dissimilar prison cell types, and data obtained from studies on germ cells imply that SUMO proteins are involved in multiple aspects of spermatogenesis. Although progress has been made in the initial characterization of sumoylated proteins during spermatogenesis, the targets of sumoylation, their respective pathways in the testis, are mostly unknown. In this chapter, I review what we know about sumoylation in somatic cells, summarize the expression patterns, suggest possible functions of SUMO proteins in testicular cells, and discuss some difficulties and perspectives on the studies of sumoylation during spermatogenesis.

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