Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 1: Background to spermatogenesis, spermatogonia, and spermatocytes

The cytoplasmic droplet may be indicative of sperm motility and normal spermiogenesis

Although the cytoplasm of spermatids is removed at the end of spermiogenesis, a tiny portion is usually retained in the sperm flagellum, which is termed the cytoplasmic droplet (CD) in mammals. CDs are believed to play a role in sperm volume adaptation. However, we have noticed that epididymal spermatozoa that display initial (flagellation in situ) and progressive motility mostly possess CDs, whereas spermatozoa without CDs are rarely motile, suggesting that CDs have a role in motility development during sperm epididymal maturation. In the present study, we analyzed the relationship between the presence or absence of CDs, motility development and positional changes of CDs during sperm epididymal maturation in mice and monkeys. We also examined CDs on spermatozoa of three knockout mouse lines with late spermiogenic defects. Our data suggest that the CD is a normal organelle transiently present exclusively on epididymal spermatozoa, and normal CD morphology and location are associated with normal motility development during epididymal maturation of spermatozoa. Abnormal CD formation, e.g., a complete lack of CDs or ectopic CDs, is indicative of defective spermiogenesis. If CDs are essential for sperm motility development, then CDs may represent an ideal drug target for the development of non-hormonal male contraceptives.

Characterization of the pre-meiotic S phase through incorporation of BrdU during spermatogenesis in the rat

Seminiferous tubules in mammals have histological arrangements defined by the associations between somatic cells and germ cells. The processes of DNA synthesis in meiotic and mitotic cells have different features that are not easily distinguishable through morphological means. In order to characterize the pre-meiotic S phase, 5-bromo-2'-deoxyuridine (BrdU) was injected intraperitoneally into Wistar rats, which were sacrificed 30 min, 2 hr, and 24 hr after injection. We found three different labeling patterns. One of these patterns was characterized by a distribution of the label in the form of speckles, most of which were associated with the nuclear envelope (labeling type I). We suggest that this pattern is due to mitotic DNA synthesis of type B spermatogonia. Labeling type II consisted of labeled foci scattered throughout the nuclear volume, which can be correlated with preleptotenic cells in pre-meiotic DNA synthesis. After 24 hr of incorporation, a third type of labeling, characterized by large speckles, was found to be related to cells in the "bouquet" stage; that is, cells in transition between the leptotene and zygotene phases. Our results indicate that BrdU incorporation induces different labeling patterns in the mitotic and pre-meiotic S phases and thus makes it possible to identify somatic and germinal cells.

Mouse sperm acquire a new structure on the apical hook during epididymal maturation

Spermatozoa emerging from the testis undergo a maturation process in the epididymis during which they change morphologically, biochemically and physiologically to gain motility and the ability to fertilize ova. We examined mouse epididymal sperm with immunostaining and transmission electron microscopy (EM) and identified a previously unknown structure on the apical hook. The structure has a coiled configuration around 11 nm in thickness and is present at the tip of each corner of the triangular-rod shaped perforatorium. Surveying sperm isolated from various regions of the epididymis indicated that mouse sperm acquire the hook rim (HR) structure during its passage through the proximal two-thirds of the caput epididymidis. The structure withstands vigorous sonication and harsh chemical treatments and remains intact after the acrosome reaction. Its location and sturdiness suggest a function in protecting the apical hook from mechanical wear during fertilization. Our EM images of epididymal sperm also revealed additional novel structures as well as lateral asymmetry of the sperm head, indicating that mouse sperm head has a structure more complex than previously recognized.

Epigenetics in radiation biology: a new research frontier

The number of people that receive exposure to ionizing radiation (IR) via occupational, diagnostic, or treatment-related modalities is progressively rising. It is now accepted that the negative consequences of radiation exposure are not isolated to exposed cells or individuals. Exposure to IR can induce genome instability in the germline, and is further associated with transgenerational genomic instability in the offspring of exposed males. The exact molecular mechanisms of transgenerational genome instability have yet to be elucidated, although there is support for it being an epigenetically induced phenomenon. This review is centered on the long-term biological effects associated with IR exposure, mainly focusing on the epigenetic mechanisms (DNA methylation and small RNAs) involved in the molecular etiology of IR-induced genome instability, bystander and transgenerational effects. Here, we present evidence that IR-mediated effects are maintained by epigenetic mechanisms, and demonstrate how a novel, male germline-specific, small RNA pathway is posited to play a major role in the epigenetic inheritance of genome instability.

Differential expression of PRAMEL1, a cancer/testis antigen, during spermatogenesis in the mouse

PRAME belongs to a group of cancer/testis antigens (CTAs) that are characterized by their restricted expression in normal gametogenic tissues and a variety of tumors. The PRAME family is one of the most amplified gene families in the mouse and other mammalian genomes. Members of the PRAME gene family encode leucine-rich repeat (LRR) proteins functioning as transcription regulators in cancer cells. However, the role of PRAME in normal gonads is unknown. The objective of this study is to characterize the temporal and spatial expression of the mouse Pramel1 gene, and to determine the cellular localization of the PRAMEL1 protein during the mouse spermatogenesis. Our results indicated that the mouse Pramel1 was expressed in testis only. The mRNA and protein expression level was low in the newborn testes, and gradually increased from 1- to 3-week-old testes, and then remained constant after three weeks of age. Immunofluorescent staining on testis sections with the mouse PRAMEL1 antibody revealed that PRAMEL1 was localized in the cytoplasm of spermatocytes and the acrosomal region of round, elongating and elongated spermatids. Further analyses on the testis squash preparation and spermatozoa at a subcellular level indicated that the protein localization patterns of PRAMEL1 were coordinated with morphological alterations during acrosome formation in spermatids, and were significantly different in connecting piece, middle piece and principal piece of the flagellum between testicular and epididymal spermatozoa. Collectively, our results suggest that PRAMEL1 may play a role in acrosome biogenesis and sperm motility.

Effects of exposure to bisphenol A during pregnancy and lactation on the testicular morphology and caspase-3 protein expression of ICR pups

Bisphenol A (BPA), a xenoestrogen and endocrine-disrupting chemical, is a cause for concern due to its being a potential human carcinogen. The aim of this study was to investigate the effects of continued maternal exposure to BPA on the testicular structures and expression of caspase-3 protein in male ICR offspring during pregnancy and lactation and explore its possible mechanism. Pregnant ICR mice were divided into two control groups, which were either given or not given the solvent dimethyl sulfoxide (DMSO) and three treatment groups, which were gavaged with water-soluble BPA dissolved in DMSO at three different concentrations from gestational day 0 to weaning on postnatal day (PND) 21. The number of mice pups and ratios of males to females were recorded. On PND 21, male offspring were sacrificed to measure their wet weights and testicular coefficients. Electron microscopy was used to observe testicular morphological changes, Hoechst 33258 staining to detect cell apoptosis and immunohistochemistry to measure caspase-3 expression. Although there was no significant difference between offspring of the control group and the treatment group in litter size and male-female ratio (P>0.05), the testicular viscera coefficient in the latter decreased (P<0.01). Specifically, compared with offspring of the control group, in addition to increased cell apoptosis, those of the treatment groups were found to have changes in mitochondrial and endoplasmic reticulum in their spermatogenous, Sertoli, Leydig and peritubular myoid cells, which were concomitant with an elevated expression of caspase-3 in the cytoplasm (P<0.01). In conclusion, exposure of pregnant mice to BPA during pregnancy and lactation has some toxic effects on the testes of male ICR offspring and these may originate from increased apoptosis.

The mouse transcription factor-like 5 gene encodes a protein localized in the manchette and centriole of the elongating spermatid

Spermiogenesis is the final phase of spermatogenesis. During this process, haploid round spermatids differentiate into spermatozoa, with dramatic morphological changes, including elongation and condensation of the nuclei, and formation of the flagella. Meig1 is one of many genes involved in the regulation of this process. Male mice deficient in MEIG1 are sterile with a severe defect in spermiogenesis, associated with dramatic disruption of the spermatid manchette and failure of flagellogenesis. A yeast two-hybrid screen using full-length MEIG1 as bait identified transcription factor-like 5 protein (TCFL5) as a putative interacting proteins. Interestingly, this protein was also identified as a potential binding partner of SPAG16, another protein essential for spermatogenesis, and also a binding partner of MEIG1. The interaction between TCFL5 and MEIG1 was confirmed in cultured cells over-expressing the two proteins. The mouse Tcfl5 transcript is present only in the testis, and its expression is significantly increased during spermiogenesis. However, little is known about TCFL5 protein and its role in male germ cells. A rabbit polyclonal antibody was generated against the C-terminal region of TCFL5. Mouse TCFL5 protein was expressed in the testis but not in mature spermatozoa. During the first wave of spermatogenesis, TCFL5 expression was dramatically increased at day 30 after birth. In the testis and a mixture of dispersed testicular cells, the protein co-localized with α-tubulin, a manchette marker in early elongating spermatids. The protein also localized in the centrioles of late elongating spermatids. No obvious differences in TCFL5 epitope abundance and localization were observed between wild type and the Meig1-deficient mice. These findings suggest that TCFL5 may play a role upstream of MEIG1 action, and based on putative binding partners and localization is likely to be involved in spermiogenesis and formation of the sperm flagella.

Intercellular adhesion molecules (ICAMs) and spermatogenesis

BACKGROUND

During the seminiferous epithelial cycle, restructuring takes places at the Sertoli-Sertoli and Sertoli-germ cell interface to accommodate spermatogonia/spermatogonial stem cell renewal via mitosis, cell cycle progression and meiosis, spermiogenesis and spermiation since developing germ cells, in particular spermatids, move 'up and down' the seminiferous epithelium. Furthermore, preleptotene spermatocytes differentiated from type B spermatogonia residing at the basal compartment must traverse the blood-testis barrier (BTB) to enter the adluminal compartment to prepare for meiosis at Stage VIII of the epithelial cycle, a process also accompanied by the release of sperm at spermiation. These cellular events that take place at the opposite ends of the epithelium are co-ordinated by a functional axis designated the apical ectoplasmic specialization (ES)-BTB-basement membrane. However, the regulatory molecules that co-ordinate cellular events in this axis are not known.

METHODS

Literature was searched at http://www.pubmed.org and http://scholar.google.com to identify published findings regarding intercellular adhesion molecules (ICAMs) and the regulation of this axis.

RESULTS

Members of the ICAM family, namely ICAM-1 and ICAM-2, and the biologically active soluble ICAM-1 (sICAM-1) are the likely regulatory molecules that co-ordinate these events. sICAM-1 and ICAM-1 have antagonistic effects on the Sertoli cell tight junction-permeability barrier, involved in Sertoli cell BTB restructuring, whereas ICAM-2 is restricted to the apical ES, regulating spermatid adhesion during the epithelial cycle. Studies in other epithelia/endothelia on the role of the ICAM family in regulating cell movement are discussed and this information has been evaluated and integrated into studies of these proteins in the testis to create a hypothetical model, depicting how ICAMs regulate junction restructuring events during spermatogenesis.

CONCLUSIONS

ICAMs are crucial regulatory molecules of spermatogenesis. The proposed hypothetical model serves as a framework in designing functional experiments for future studies.

Phenotypic assessment of male fertility status in transgenic animal models

This chapter describes the approach to define the cause of male infertility in a genetically modified male mouse. It provides a guide to the establishment of the infertility status and whether it is due to the failure of mating or due to abnormalities of the sperm output, motility, and morphology. Further assessments define the nature of the spermatogenic defects and their severity and are designed to determine the pathogenic mechanisms involved.

LINCing the nuclear envelope to gametogenesis

Gametogenesis combines two important features: reduction of the genome content from diploid to haploid by carefully partitioning chromosomes, and the subsequent differentiation into fertilization-competent gametes, which in males is characterized by profound nuclear restructuring. These are quite difficult tasks and require a tight coordination of different cellular mechanisms. Recent studies in the field established a key role for LINC complexes in both meiosis and sperm head formation. LINC complexes comprise SUN and KASH domain proteins that form nuclear envelope (NE) bridges, linking the nucleoskeleton to the cytoskeleton. They are well known for their crucial roles in diverse cellular and developmental processes, such as nuclear positioning and cell polarization. In this review, we highlight key roles ascribed to LINC complexes and to the nucleocytoskeletal connection in gametogenesis. First, we give a short overview about the general features of LINC components and the profound reorganization of the NE in germ cells. We then focus on specific roles of LINC complexes in meiotic chromosome dynamics and their impact on pairing, synapsis, and recombination. Finally, we provide an update of the mechanisms controlling sperm head formation and discuss the role of sperm-specific LINC complexes in nuclear shaping and their relation to specialized cytoskeletal structures that form concurrently with nuclear restructuring and sperm elongation.

MARCH7 E3 ubiquitin ligase is highly expressed in developing spermatids of rats and its possible involvement in head and tail formation

Spermatogenesis is a highly complicated metamorphosis process of male germ cells. Recent studies have provided evidence that the ubiquitin-proteasome system plays an important role in sperm head shaping, but the underlying mechanism is less understood. In this study, we localized membrane-associated RING-CH (MARCH)7, an E3 ubiquitin ligase, in rat testis. Northern blot analysis showed that March7 mRNA is expressed ubiquitously but highly in the testis and ovary. In situ hybridization of rat testis demonstrated that March7 mRNA is expressed weakly in spermatogonia and its level is gradually increased as they develop. Immunohistochemical analysis detected MARCH7 protein expression in spermiogenic cells from late round spermatids to elongated spermatids and in epididymal spermatozoa. Moreover, MARCH7 was found to be localized to the caudal end of the developing acrosome of late round and elongating spermatids, colocalizing with β-actin, a component of the acroplaxome. In addition, MARCH7 was also detected in the developing flagella and its expression levels were prominent in elongated spermatids. We also showed that MARCH7 catalyzes lysine 48 (K48)-linked ubiquitination. Immunolocalization studies revealed that K48-linked ubiquitin chains were detected in the heads of elongating spermatids and in the acrosome/acroplaxome, neck, midpiece and cytoplasmic lobes of elongated spermatids. These results suggest that MARCH7 is involved in spermiogenesis by regulating the structural and functional integrity of the head and tail of developing spermatids.

Genetics of germ cell development

The germ line represents a continuous cellular link between generations and between species, but the germ cells themselves develop in a specialized, organism-specific context. The model organisms Caenorhabditis elegans, Drosophila melanogaster and the mouse display striking similarities, as well as major differences, in the means by which they control germ cell development. Recent developments in genetic technologies allow a more detailed comparison of the germ cells of these three organisms than has previously been possible, shedding light not only on universal aspects of germline regulation, but also on the control of the pluripotent state in vivo and on the earliest steps of embryogenesis. Here, we highlight themes from the comparison of these three alternative strategies for navigating the fundamental cycle of sexual reproduction.

Tissue-specific functional networks for prioritizing phenotype and disease genes

Integrated analyses of functional genomics data have enormous potential for identifying phenotype-associated genes. Tissue-specificity is an important aspect of many genetic diseases, reflecting the potentially different roles of proteins and pathways in diverse cell lineages. Accounting for tissue specificity in global integration of functional genomics data is challenging, as “functionality” and “functional relationships” are often not resolved for specific tissue types. We address this challenge by generating tissue-specific functional networks, which can effectively represent the diversity of protein function for more accurate identification of phenotype-associated genes in the laboratory mouse. Specifically, we created 107 tissue-specific functional relationship networks through integration of genomic data utilizing knowledge of tissue-specific gene expression patterns. Cross-network comparison revealed significantly changed genes enriched for functions related to specific tissue development. We then utilized these tissue-specific networks to predict genes associated with different phenotypes. Our results demonstrate that prediction performance is significantly improved through using the tissue-specific networks as compared to the global functional network. We used a testis-specific functional relationship network to predict genes associated with male fertility and spermatogenesis phenotypes, and experimentally confirmed one top prediction, Mbyl1. We then focused on a less-common genetic disease, ataxia, and identified candidates uniquely predicted by the cerebellum network, which are supported by both literature and experimental evidence. Our systems-level, tissue-specific scheme advances over traditional global integration and analyses and establishes a prototype to address the tissue-specific effects of genetic perturbations, diseases and drugs.

Tissue specificity is an important aspect of many genetic diseases, reflecting the potentially different roles of proteins and pathways in diverse cell lineages. We propose an effective strategy to model tissue-specific functional relationship networks in the laboratory mouse. We integrated large scale genomics datasets as well as low-throughput tissue-specific expression profiles to estimate the probability that two proteins are co-functioning in the tissue under study. These networks can accurately reflect the diversity of protein functions across different organs and tissue compartments. By computationally exploring the tissue-specific networks, we can accurately predict novel phenotype-related gene candidates. We experimentally confirmed a top candidate gene, Mybl1, to affect several male fertility phenotypes, predicted based on male-reproductive system-specific networks and we predicted candidates related to a rare genetic disease ataxia, which are supported by experimental and literature evidence. The above results demonstrate the power of modeling tissue-specific dynamics of co-functionality through computational approaches.

Motile sperm organelle morphology evaluation-selected globozoospermic human sperm with an acrosomal bud exhibits novel patterns and higher levels of phospholipase C zeta

STUDY QUESTION

Does motile sperm organelle morphology examination (MSOME) affect levels and localization patterns of the oocyte activation factor phospholipase C zeta (PLCζ) in globozoospermic sperm with and without an acrosomal bud?

SUMMARY ANSWER

MSOME identified round-headed globozoospermic sperm with increased levels of PLCζ relative to sperm from the same sample that did not undergo MSOME, and identified novel patterns of PLCζ localization in sperm exhibiting an acrosomal bud.

WHAT IS KNOWN ALREADY

Absence or reduction in the level of PLCζ in the sperm head, abnormal localization patterning, or defective functional ability as a result of PLCζ gene mutation, have been linked to certain types of human male factor infertility in which oocyte activation is deficient. It has been determined that a subpopulation of sperm (1%) from a patient exhibiting 100% globozoospermia presented with an acrosome bud upon MSOME. A cycle of intracytoplasmic morphologically selected sperm injection, carried out with sperm exhibiting an acrosomal bud led to pregnancy and birth of a healthy baby boy, without the use of assisted oocyte activation (AOA).

STUDY DESIGN, SIZE, DURATION

Immunofluorescent analysis of PLCζ in globozoospermic sperm from three patients, before and after MSOME.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Quantitative immunofluorescence was used to investigate PLCζ levels and localization patterns in individual sperm (n = 1 patient) identified by MSOME and isolated by micromanipulation, and presenting with and without the acrosomal bud. A secondary aim was to investigate levels and localization patterns of PLCζ in sperm before and after MSOME from two other globozoospermic men.

MAIN RESULTS AND THE ROLE OF CHANCE

Non-globozoospermic control sperm exhibited characteristic localization patterns of PLCζ immunofluorescence. Completely round-headed globozoospermic sperm from patients 1-3 were either devoid of PLCζ immunofluorescence, or exhibited an abnormal, punctate, pattern of PLCζ localization. PLCζ immunofluorescence in sperm exhibiting an acrosomal bud was observed in the midpiece with varying fluorescent intensity and was detected in 28.5% of such sperm. The majority of sperm with an acrosomal bud (43.0%) exhibited punctate patterns of PLCζ localization within the sperm head. A further 28.5% of sperm exhibited PLCζ in both the head and the midpiece. Total levels of PLCζ, and the proportions of sperm exhibiting PLCζ immunoreactivity, showed significant variance (P ≤ 0.05) amongst control [45.8 arbitrary units (a.u.) and 95.7%, respectively], non-MSOME-selected (25.9 a.u. and 46.1%, respectively) and MSOME-selected globozoospermic sperm (33.4 a.u. and 65.0%, respectively). Total levels of PLCζ immunofluorescence, and proportions of sperm exhibiting PLCζ immunoreactivity, in control sperm was significantly higher (P≤ 0.05) compared with non-MSOME-selected sperm, but not significantly different from MSOME-selected sperm.

LIMITATIONS, REASONS FOR CAUTION

The low numbers of sperm analysed may not be ideal for conclusive statistical analysis. Evaluation of the effects of MSOME on morphologically normal sperm would confirm conclusions.

WIDER IMPLICATIONS OF THE FINDINGS

The present findings provide hope for the future treatment of globozoospermia without the need for AOA, and provide further evidence for the clinical application of PLCζ as a therapeutic and prognostic tool.

STUDY FUNDING/COMPETING INTEREST(S)

The research described herein was funded by the Nuffield Department of Obstetrics and Gynaecology, University of Oxford. The authors report no conflict of interest.

Proteomic changes in rat spermatogenesis in response to in vivo androgen manipulation; impact on meiotic cells

The production of mature sperm is reliant on androgen action within the testis, and it is well established that androgens act on receptors within the somatic Sertoli cells to stimulate male germ cell development. Mice lacking Sertoli cell androgen receptors (AR) show late meiotic germ cell arrest, suggesting Sertoli cells transduce the androgenic stimulus co-ordinating this essential step in spermatogenesis. This study aimed to identify germ cell proteins responsive to changes in testicular androgen levels and thereby elucidate mechanisms by which androgens regulate meiosis. Testicular androgen levels were suppressed for 9 weeks using testosterone and estradiol-filled silastic implants, followed by a short period of either further androgen suppression (via an AR antagonist) or the restoration of intratesticular testosterone levels. Comparative proteomics were performed on protein extracts from enriched meiotic cell preparations from adult rats undergoing androgen deprivation and replacement in vivo. Loss of androgenic stimulus caused changes in proteins with known roles in meiosis (including Nasp and Hsp70–2), apoptosis (including Diablo), cell signalling (including 14-3-3 isoforms), oxidative stress, DNA repair, and RNA processing. Immunostaining for oxidised DNA adducts confirmed spermatocytes undergo oxidative stress-induced DNA damage during androgen suppression. An increase in PCNA and an associated ubiquitin-conjugating enzyme (Ubc13) suggested a role for PCNA-mediated regulation of DNA repair pathways in spermatocytes. Changes in cytoplasmic SUMO1 localisation in spermatocytes were paralleled by changes in the levels of free SUMO1 and of a subunit of its activating complex, suggesting sumoylation in spermatocytes is modified by androgen action on Sertoli cells. We conclude that Sertoli cells, in response to androgens, modulate protein translation and post-translational events in spermatocytes that impact on their metabolism, survival, and completion of meiosis.

Mili and Miwi target RNA repertoire reveals piRNA biogenesis and function of Miwi in spermiogenesis

Germ cells implement elaborate mechanisms to protect their genetic material and to regulate gene expression during differentiation. Piwi proteins bind piRNAs, a class of small germline RNAs whose biogenesis and functions are still largely elusive. We employed high throughput sequencing after crosslinking and immunoprecipitation (HITS-CLIP) coupled with RNA-Seq to characterize the genome-wide target RNA repertoire of Mili (Piwil2) and Miwi (Piwil1), two Piwi proteins expressed in mouse postnatal testis. We report the in vivo pathway of primary piRNA biogenesis and implicate distinct nucleolytic activities that process Piwi-bound precursor transcripts. Our studies indicate that pachytene piRNAs are the end products of RNA processing. HITS-CLIP demonstrates that Miwi binds spermiogenic mRNAs directly, without utilizing piRNAs as guides, and independent biochemical analyses of testis mRNA-ribonucleoproteins (mRNPs) establishes that Miwi functions in the formation of mRNP complexes that stabilize mRNAs essential for spermiogenesis.

Compartmentalization and regulation of iron metabolism proteins protect male germ cells from iron overload

The universal importance of iron, its high toxicity, and complex chemistry present a challenge to biological systems in general and to protected compartments in particular. The high mitotic rate and avid mitochondriogenesis of developing male germ cells imply high iron requirements. Yet access to germ cells is tightly regulated by the blood-testis barrier that protects the meiotic and postmeiotic germ cells. To elucidate how iron is supplied to developing male germ cells, we analyzed iron deposition and iron transport proteins in testes of mice with iron overload and with genetic ablation of the iron regulators Hfe and iron regulatory protein 2. Iron accumulated mainly around seminiferous tubules, and only small amounts localized within the seminiferous tubules. The localization and regulation of proteins involved in iron import, storage, and export such as transferrin, transferrin receptor, the divalent metal transporter-1, cytosolic ferritin, and ferroportin strongly support a model of a largely autonomous iron cycle within seminiferous tubules. We show evidence that ferritin secretion from Sertoli cells may play an important role in iron acquisition of primary spermatocytes. During spermatogenic development iron is carried along from primary spermatocytes to spermatids, and from spermatids iron is recycled to the apical compartment of Sertoli cells, which traffic it back to a new generation of spermatocytes. Losses are replenished by the peripheral circulation. Such an internal iron cycle essentially detaches the iron homeostasis within the seminiferous tubule from the periphery and protects developing germ cells from iron fluctuations. This model explains how compartmentalization can optimize cellular and systemic nutrient homeostasis.

Complex N-glycans are essential, but core 1 and 2 mucin O-glycans, O-fucose glycans, and NOTCH1 are dispensable, for mammalian spermatogenesis

To identify roles in spermatogenesis for major subclasses of N- and O-glycans and Notch signaling, male mice carrying floxed C1galt1, Pofut1, Notch1 or Mgat1 alleles and a testis-specific Cre recombinase transgene were generated. T-synthase (C1GALT1) transfers Gal to generate core 1 and core 2 mucin O-glycans; POFUT1 transfers O-fucose to particular epidermal growth factor-like repeats and is essential for canonical Notch signaling; and MGAT1 (GlcNAcT-I) transfers GlcNAc to initiate hybrid and complex N-glycan synthesis. Cre recombinase transgenes driven by various promoters were investigated, including Stra8-iCre expressed in spermatogonia, Sycp1-Cre expressed in spermatocytes, Prm1-Cre expressed in spermatids, and AMH-Cre expressed in Sertoli cells. All Cre transgenes deleted floxed alleles, but efficiencies varied widely. Stra8-iCre was the most effective, deleting floxed Notch1 and Mgat1 alleles with 100% efficiency and floxed C1galt1 and Pofut1 alleles with ~80% efficiency, based on transmission of deleted alleles. Removal of C1galt1, Pofut1, or Notch1 in spermatogonia had no effect on testicular weight, histology, or fertility. However, males in which the synthesis of complex N-glycans was blocked by deletion of Mgat1 in spermatogonia did not produce sperm. Spermatogonia, spermatocytes, and spermatids were generated, but most spermatids formed giant multinucleated cells or symplasts, and apoptosis was increased. Therefore, although core 1 and 2 mucin O-glycans, NOTCH1, POFUT1, O-fucose glycans, and Notch signaling are dispensable, MGAT1 and complex N-glycans are essential for spermatogenesis.

Genome-wide association study identifies candidate genes for male fertility traits in humans

Despite the fact that hundreds of genes are known to affect fertility in animal models, relatively little is known about genes that influence natural fertility in humans. To broadly survey genes contributing to variation in male fertility, we conducted a genome-wide association study (GWAS) of two fertility traits (family size and birth rate) in 269 married men who are members of a founder population of European descent that proscribes contraception and has large family sizes. Associations between ∼250,000 autosomal SNPs and the fertility traits were examined. A total of 41 SNPs with p ≤ 1 × 10(-4) for either trait were taken forward to a validation study of 123 ethnically diverse men from Chicago who had previously undergone semen analyses. Nine (22%) of the SNPs associated with reduced fertility in the GWAS were also associated with one or more of the ten measures of reduced sperm quantity and/or function, yielding 27 associations with p values < 0.05 and seven with p values < 0.01 in the validation study. On the basis of 5,000 permutations of our data, the probabilities of observing this many or more small p values were 0.0014 and 5.6 × 10(-4), respectively. Among the nine associated loci, outstanding candidates for male fertility genes include USP8, an essential deubiquitinating enzyme that has a role in acrosome assembly; UBD and EPSTI1, which have potential roles in innate immunity; and LRRC32, which encodes a latent transforming growth factor β (TGF-β) receptor on regulatory T cells. We suggest that mutations in these genes that are more severe may account for some of the unexplained infertility (or subfertility) in the general population.

The RNase III enzyme DROSHA is essential for microRNA production and spermatogenesis

DROSHA is a nuclear RNase III enzyme responsible for cleaving primary microRNAs (miRNAs) into precursor miRNAs and thus is essential for the biogenesis of canonical miRNAs. DICER is a cytoplasmic RNase III enzyme that not only cleaves precursor miRNAs to produce mature miRNAs but also dissects naturally formed/synthetic double-stranded RNAs to generate small interfering RNAs (siRNAs). To investigate the role of canonical miRNA and/or endogenous siRNA production in spermatogenesis, we generated Drosha or Dicer conditional knock-out (cKO) mouse lines by inactivating Drosha or Dicer exclusively in spermatogenic cells in postnatal testes using the Cre-loxp strategy. Both Drosha and Dicer cKO males were infertile due to disrupted spermatogenesis characterized by depletion of spermatocytes and spermatids leading to oligoteratozoospermia or azoospermia. The developmental course of spermatogenic disruptions was similar at morphological levels between Drosha and Dicer cKO males, but Drosha cKO testes appeared to be more severe in spermatogenic disruptions than Dicer cKO testes. Microarray analyses revealed transcriptomic differences between Drosha- and Dicer-null pachytene spermatocytes or round spermatids. Although levels of sex-linked mRNAs were mildly elevated, meiotic sex chromosome inactivation appeared to have occurred normally. Our data demonstrate that unlike DICER, which is required for the biogenesis of several small RNA species, DROSHA is essential mainly for the canonical miRNA production, and DROSHA-mediated miRNA production is essential for normal spermatogenesis and male fertility.

An essential role for katanin p80 and microtubule severing in male gamete production

Katanin is an evolutionarily conserved microtubule-severing complex implicated in multiple aspects of microtubule dynamics. Katanin consists of a p60 severing enzyme and a p80 regulatory subunit. The p80 subunit is thought to regulate complex targeting and severing activity, but its precise role remains elusive. In lower-order species, the katanin complex has been shown to modulate mitotic and female meiotic spindle dynamics and flagella development. The in vivo function of katanin p80 in mammals is unknown. Here we show that katanin p80 is essential for male fertility. Specifically, through an analysis of a mouse loss-of-function allele (the Taily line), we demonstrate that katanin p80, most likely in association with p60, has an essential role in male meiotic spindle assembly and dissolution and the removal of midbody microtubules and, thus, cytokinesis. Katanin p80 also controls the formation, function, and dissolution of a microtubule structure intimately involved in defining sperm head shaping and sperm tail formation, the manchette, and plays a role in the formation of axoneme microtubules. Perturbed katanin p80 function, as evidenced in the Taily mouse, results in male sterility characterized by decreased sperm production, sperm with abnormal head shape, and a virtual absence of progressive motility. Collectively these data demonstrate that katanin p80 serves an essential and evolutionarily conserved role in several aspects of male germ cell development.

Microtubules are critical components of cells, acting as a “scaffold” for the movement of organelles and proteins within the cytoplasm. The control of microtubule length, number, and movement is essential for many cellular processes, including division, architecture, and migration. We have defined the role of the microtubule severing protein katanin p80 in male germ cell development. Male mice carrying a point mutation in the p80 gene are sterile as a consequence of low numbers of sperm, abnormal sperm morphology, and poor motility (ability to “swim”). We show that this mutation is associated with defects in microtubule structures involved in the division of immature sperm cells, in structures that shape the sperm head, and in the sperm tail, which is essential for sperm movement in the female reproductive tract. This study is the first to show that katanin p80, via its effects on microtubule dynamics within the testis, is required for male fertility.

Preparation of enriched mouse syncitia-free pachytene spermatocyte cell suspensions

Spermatogenesis comprises a complex succession of steps of mitosis, meiosis, and differentiation, starting with the commitment of diploid spermatogonial stem cells to differentiate and ending with the formation of haploid spermatozoa. Rodent models have been routinely used to study germ cell development and reproductive toxicology, since they present many similarities with their human counterpart while offering the advantage of recapitulating within a few weeks a process that normally takes years to occur. This article describes a method to isolate subpopulations of adult germ cells, more specifically pachytene spermatocytes, using two successive gradients, without using an elutriation centrifuge, a specialized device not available in many laboratories. Moreover, the method was designed to isolate enriched pachytene spermatocytes preparations devoid of contaminating syncitia, often formed in response to toxicants or environmental insults.

Chromatin remodelling initiation during human spermiogenesis

During the last phase of spermatogenesis, spermiogenesis, haploid round spermatids metamorphose towards spermatozoa. Extensive cytoplasmic reduction and chromatin remodelling together allow a dramatic decrease of cellular, notably nuclear volume. DNA packing by a nucleosome based chromatin structure is largely replaced by a protamine based one. At the cytoplasmic level among others the acrosome and perinuclear theca (PNT) are formed. In this study we describe the onset of chromatin remodelling to occur concomitantly with acrosome and PNT development. In spread human round spermatid nuclei, we show development of a DAPI-intense doughnut-like structure co-localizing with the acrosomal sac and sub acrosomal PNT. At this structure we observe the first gradual decrease of nucleosomes and several histones. Histone post-translational modifications linked to chromatin remodelling such as H4K8ac and H4K16ac also delineate the doughnut, that is furthermore marked by H3K9me2. During the capping phase of acrosome development, the size of the doughnut-like chromatin domain increases, and this area often is marked by uniform nucleosome loss and the first appearance of transition protein 2 and protamine 1. In the acrosome phase at nuclear elongation, chromatin remodelling follows the downward movement of the marginal ring of the acrosome. Our results indicate that acrosome development and chromatin remodelling are interacting processes. In the discussion we relate chromatin remodelling to the available data on the nuclear envelope and the linker of nucleoskeleton and cytoskeleton (LINC) complex of spermatids, suggesting a signalling route for triggering chromatin remodelling.

Paternal age effect mutations and selfish spermatogonial selection: causes and consequences for human disease

Advanced paternal age has been associated with an increased risk for spontaneous congenital disorders and common complex diseases (such as some cancers, schizophrenia, and autism), but the mechanisms that mediate this effect have been poorly understood. A small group of disorders, including Apert syndrome (caused by FGFR2 mutations), achondroplasia, and thanatophoric dysplasia (FGFR3), and Costello syndrome (HRAS), which we collectively term "paternal age effect" (PAE) disorders, provides a good model to study the biological and molecular basis of this phenomenon. Recent evidence from direct quantification of PAE mutations in sperm and testes suggests that the common factor in the paternal age effect lies in the dysregulation of spermatogonial cell behavior, an effect mediated molecularly through the growth factor receptor-RAS signal transduction pathway. The data show that PAE mutations, although arising rarely, are positively selected and expand clonally in normal testes through a process akin to oncogenesis. This clonal expansion, which is likely to take place in the testes of all men, leads to the relative enrichment of mutant sperm over time-explaining the observed paternal age effect associated with these disorders-and in rare cases to the formation of testicular tumors. As regulation of RAS and other mediators of cellular proliferation and survival is important in many different biological contexts, for example during tumorigenesis, organ homeostasis and neurogenesis, the consequences of selfish mutations that hijack this process within the testis are likely to extend far beyond congenital skeletal disorders to include complex diseases, such as neurocognitive disorders and cancer predisposition.

STK31(TDRD8) is dynamically regulated throughout mouse spermatogenesis and interacts with MIWI protein

Tudor-domain-containing proteins (TDRDs) are suggested to be critical regulators of germinal granules assembly involved in Piwi-interacting RNAs (piRNAs)-mediated pathways, of which associated components and the underlying functional mechanisms, however, remain to be elucidated. We herein characterized the expression pattern of STK31, a member of TDRDs subfamily (also termed as TDRD8), throughout spermatogenesis during mouse postnatal development. RT-PCR and Western blot verified its preferential expression in testis, but not in any other somatic tissues, in addition to embryonic stem cells. Immunofluorescent staining demonstrated that STK31 was confined to granules-like structures in mid-to-late spermatocyte cytoplasm and to acrosomal cap starting at steps 7-8 of spermatids. Furthermore, STK31 retained its localization to equatorial segment of acrosome during epididymal maturation, capacitation, and acrosome reaction. Co-immunoprecipitation assay in vivo and in vitro confirmed MIWI is a bona fide partner of STK31 in mice testes, in combination with LC/MS identification. We also discovered a group of heat shock proteins specifically associated with STK31 in vivo. Our findings suggest mouse STK31 could be a potential nuage-associated protein in the cytoplasm of mid-to-late spermatocytes and play pivotal roles related to fertilization.

Identification of SAMT family proteins as substrates of MARCH11 in mouse spermatids

MARCH11, a RING-finger transmembrane ubiquitin ligase, is predominantly expressed in spermatids and localized to the trans-Golgi network (TGN) and multivesicular bodies (MVBs). Because ubiquitination acts as a sorting signal of cargo proteins, MARCH11 has been postulated to mediate selective protein sorting via the TGN-MVB pathway. However, the physiological substrate of MARCH11 has not been identified. In this study, we have identified and characterized SAMT1, a member of a novel 4-transmembrane protein family, which consists of four members. Samt1 mRNA and its expression product were found to be specific to the testis and were first detected in germ cells 25 days after birth in mice. Immunohistochemical analysis further revealed that SAMT1 was specifically expressed in haploid spermatids during the cap and acrosome phases. Confocal microscopic analysis showed that SAMT1 co-localized with MARCH11 as well as with fucose-containing glycoproteins, another TGN/MVB marker, and LAPM2, a late endosome/lysosome marker. Furthermore, we found that MARCH11 could increase the ubiquitination of SAMT1 and enhance its lysosomal delivery and degradation in an E3 ligase activity-dependent manner. In addition, the C-terminal region of SAMT1 was indispensable for its ubiquitination and proper localization. The other member proteins of the SAMT family also showed similar expression profile, intracellular localization, and biochemical properties, including ubiquitination by MARCH11. These results suggest that SAMT family proteins are physiological substrates of MARCH11 and are delivered to lysosomes through the TGN-MVB pathway by a ubiquitin-dependent sorting system in mouse spermatids.

Arylsulfatase A deficiency causes seminolipid accumulation and a lysosomal storage disorder in Sertoli cells

Sulfogalactosylglycerolipid (SGG) is the major sulfoglycolipid of male germ cells. During spermatogenesis, apoptosis occurs in >50% of total germ cells. Sertoli cells phagocytose these apoptotic germ cells and degrade their components using lysosomal enzymes. Here we demonstrated that SGG was a physiological substrate of Sertoli lysosomal arylsulfatase A (ARSA). SGG accumulated in Sertoli cells of Arsa(-/-) mice, and at 8 months of age, this buildup led to lysosomal swelling and other cellular abnormalities typical of a lysosomal storage disorder. This disorder likely compromised Sertoli cell functions, manifesting as impaired spermatogenesis and production of sperm with near-zero fertilizing ability in vitro. Fecundity of Arsa(-/-) males was thus reduced when they were older than 5 months. Sperm SGG is known for its roles in fertilization. Therefore, the minimal sperm fertilizing ability of 8-month-old Arsa(-/-) males may be explained by the 50% reduction of their sperm SGG levels, a result that was also observed in testicular germ cells. These unexpected decreases in SGG levels might be partly due to depletion of the backbone lipid palmitylpalmitoylglycerol that is generated from the SGG degradation pathway in Sertoli cells and normally recycled to new generations of primary spermatocytes for SGG synthesis.

Reduced numbers of Sertoli, germ, and spermatogonial stem cells in impaired spermatogenesis

A key step in the investigation of male infertility is the appropriate classification of impaired spermatogenesis. In this study, we precisely identified Sertoli and distinct germ-cell types in the rat, the mouse, and in the human testis. As a proof of principle, we studied testis biopsy samples from azoospermic patients with defined spermatogenic defects. Remarkably, we found that already the numbers of Sertoli cells, spermatogonia and a subset of spermatogonia including stem cells are significantly reduced in patients with maturation arrest at the level of primary spermatocytes (n=33) compared with patients with histologically normal spermatogenesis (n=33). In patients with hypospermatogenesis (n=44) a significant reduction of spermatogonial cell numbers was observed. The numbers of primary and diplotene spermatocytes were reduced by 84%. However, the strongest reduction (96%) was revealed in the numbers of spermatids in patients with maturation arrest. In contrast, patients with hypospermatogenesis showed only modestly reduced numbers of spermatocytes and spermatids compared with normal spermatogenesis. No correlation was found with age or obstruction. For a detailed analysis of the patients, we distinguished between 'pool of founder cells'-related deficiencies (reduced numbers of Sertoli cells, spermatogonia, and spermatogonial stem cells) and 'meiotic' deficiencies (reduced numbers of spermatocytes, meiotic divisions, and spermatids). Interestingly, patients with maturation arrest showed meiotic deficiencies (36%), while the majority additionally demonstrated deficiencies in the founder pool (58%). In contrast, patients with normal spermatogenesis most often had no deficiencies at all (45%) or founder pool-related deficiencies (33%) but an apparently normal meiosis. This is the first report showing that many infertile patients face besides meiotic defects the problem of reduced numbers of Sertoli cells, spermatogonia, and spermatogonial stem cells.

Connexins and pannexins: Coordinating cellular communication in the testis and epididymis

Gap junctions and connexins are critical for coordinating cellular functions in complex epithelia. In recent years there has been increased interest in understanding the regulation and function of gap junctions in both the testis and epididymis. Studies in transgenic mice in which connexin 43 (Cx43) is mutated or is knocked down only in Sertoli cells have demonstrated the essential role of Cx43 in spermatogenesis and differentiation of Sertoli cells. In the epididymis developmental studies have shown a role for numerous connexins in the differentiation of epithelial cells and communication between the basal cells and both principal and clear cells. In both tissues several factors, such thyroid hormones and androgens, are important in regulating expression and function of connexins. Pannexins, which form cellular channels but are structurally similar to gap junction proteins, have been identified in both testis and epididymis and, in the epididymis, are regulated by androgens. The objective of this review is to summarize the advances that have been made on the role and regulation of connexins and pannexins in the testis and epididymis and their implication in spermatogenesis and sperm maturation.

Calcium Channels in the Development, Maturation, and Function of Spermatozoa

A proper dialogue between spermatozoa and the egg is essential for conception of a new individual in sexually reproducing animals. Ca2+ is crucial in orchestrating this unique event leading to a new life. No wonder that nature has devised different Ca2+-permeable channels and located them at distinct sites in spermatozoa so that they can help fertilize the egg. New tools to study sperm ionic currents, and image intracellular Ca2+ with better spatial and temporal resolution even in swimming spermatozoa, are revealing how sperm ion channels participate in fertilization. This review critically examines the involvement of Ca2+ channels in multiple signaling processes needed for spermatozoa to mature, travel towards the egg, and fertilize it. Remarkably, these tiny specialized cells can express exclusive channels like CatSper for Ca2+ and SLO3 for K+, which are attractive targets for contraception and for the discovery of novel signaling complexes. Learning more about fertilization is a matter of capital importance; societies face growing pressure to counteract rising male infertility rates, provide safe male gamete-based contraceptives, and preserve biodiversity through improved captive breeding and assisted conception initiatives.

Testicular connexin 43, a precocious molecular target for the effect of environmental toxicants on male fertility

Many recent epidemiological, clinical and experimental findings support the hypothesis that environmental toxicants are responsible for the increasing male reproductive disorders (congenital malformations, declining sperm counts and testicular cancer) over the past 20 years. It has also been reported that exposure to these toxicants, during critical periods of development (fetal and neonatal), represents a more considerable risk for animals and humans than exposure during adulthood. However, the molecular targets for these chemicals have not been clearly identified. Recent studies showed that a family of transmembranous proteins, named connexins, regulates numerous physiological processes involved in testicular development and function, such as Sertoli and germ cell proliferation, differentiation, germ cell migration and apoptosis. In the testis, knockout strategy revealed that connexin 43, the predominant connexin in this organ, is essential for spermatogenesis. In addition, there is evidence that many environmental toxicants could alter testicular connexin 43 by dysregulation of numerous mechanisms controlling its function. In the present work, we propose first to give an overview of connexin expression and intercellular gap junction coupling in the developing fetal and neonatal testes. Second, we underline the impact of maternally chemical exposure on connexin 43 expression in the perinatal developing testis. Lastly, we attempt to link this precocious effect to male offspring fertility.

Membrane-associated RING-CH 10 (MARCH10 protein) is a microtubule-associated E3 ubiquitin ligase of the spermatid flagella

Spermiogenesis is a complex and dynamic process of the metamorphosis of spermatids into spermatozoa. There is a great deal that is still unknown regarding the regulatory mechanisms for the formation of the sperm flagellum. In this study, we determined that the membrane-associated RING-CH 10 (March10) gene is predominantly expressed in rat testis. We isolated two March10 isoforms encoding MARCH10a and MARCH10b, which are generated by alternative splicing. MARCH10a is a long RING finger protein, and MARCH10b is a short RING finger-less protein. Immunohistochemical staining revealed that the MARCH10 proteins are specifically expressed in elongating and elongated spermatids, and the expression is absent in epididymal spermatozoa. MARCH10 immunoreactivity was observed in the cytoplasmic lobes as well as the principal piece and annulus of the flagella. When overexpressed in COS7 cells, MARCH10a was localized along the microtubules, whereas MARCH10b was distributed throughout the cytoplasm. An in vitro microtubule cosedimentation assay showed that MARCH10a is directly associated with microtubules. An in vitro ubiquitination assay demonstrated that the RING finger domain of MARCH10a exhibits an E3 ubiquitin ligase activity along with the E2 ubiquitin-conjugating enzyme UBE2B. Moreover, MARCH10a undergoes proteasomal degradation by autoubiquitination in transfected COS7 cells, but this activity was abolished upon microtubule disassembly. These results suggest that MARCH10 is involved in spermiogenesis by regulating the formation and maintenance of the flagella in developing spermatids.

Purinergic signalling mobilizes mitochondrial Ca²⁺ in mouse Sertoli cells

Intimate bidirectional communication between Sertoli cells and developing germ cells ensures the integrity and efficiency of spermatogenesis. Yet, a conceptual mechanistic understanding of the physiological principles that underlie Sertoli cell autocrine and paracrine signalling is lacking. Here, we characterize a purinergic Ca(2+) signalling network in immature mouse Sertoli cells that consists of both P2X2 and P2Y2 purinoceptor subtypes, the endoplasmic reticulum and, notably, mitochondria. By combining a transgenic mouse model with a dedicated bioluminescence imaging device, we describe a novel method to monitor mitochondrial Ca(2+) mobilization in Sertoli cells at subcellular spatial and millisecond temporal resolution. Our data identify mitochondria as essential components of the Sertoli cell signalling 'toolkit' that control the shape of purinergic Ca(2+) responses, and probably several other paracrine Ca(2+)-dependent signals.

Pluripotency of male germline stem cells

The ethical issues and public concerns regarding the use of embryonic stem (ES) cells in human therapy have motivated considerable research into the generation of pluripotent stem cell lines from non-embryonic sources. Numerous reports have shown that pluripotent cells can be generated and derived from germline stem cells (GSCs) in mouse and human testes during in vitro cultivation. The gene expression patterns of these cells are similar to those of ES cells and show the typical self-renewal and differentiation patterns of pluripotent cells in vivo and in vitro. However, the mechanisms underlying the spontaneous dedifferentiation of GSCs remain to be elucidated. Studies to identify master regulators in this reprogramming process are of critical importance for understanding the gene regulatory networks that sustain the cellular status of these cells. The results of such studies would provide a theoretical background for the practical use of these cells in regenerative medicine. Such studies would also help elucidate the molecular mechanisms underlying certain diseases, such as testicular germ cell tumors.

Spermatogonial stem cells, infertility and testicular cancer

The spermatogonial stem cells (SSCs) are responsible for the transmission of genetic information from an individual to the next generation. SSCs play critical roles in understanding the basic reproductive biology of gametes and treatments of human infertility. SSCs not only maintain normal spermatogenesis, but also sustain fertility by critically balancing both SSC self-renewal and differentiation. This self-renewal and differentiation in turn is tightly regulated by a combination of intrinsic gene expression within the SSC as well as the extrinsic gene signals from the niche. Increased SSCs self-renewal at the expense of differentiation result in germ cell tumours, on the other hand, higher differentiation at the expense of self-renewal can result in male sterility. Testicular germ cell cancers are the most frequent cancers among young men in industrialized countries. However, understanding the pathogenesis of testis cancer has been difficult because it is formed during foetal development. Recent studies suggest that SSCs can be reprogrammed to become embryonic stem (ES)-like cells to acquire pluripotency. In the present review, we summarize the recent developments in SSCs biology and role of SSC in testicular cancer. We believe that studying the biology of SSCs will not only provide better understanding of stem cell regulation in the testis, but eventually will also be a novel target for male infertility and testicular cancers.

Improvements in human sperm quality by long-term in vitro co-culture with isolated porcine Sertoli cells

BACKGROUND

Spermatogenesis is a complex process where spermatogonial germ cells become spermatozoa with the indispensable support of Sertoli cells (SCs), which provide 'ad hoc' structural and nutritional support. Unfortunately, for most sperm dysfunctions, no therapies are yet available except assisted reproductive technologies (ART) that are based on the use of different culture media to preserve sperm in vitro. However, sperm culture is only possible for short periods of time, since long-term culture would invariably and irreversibly damage the cells with negative impact on their fertilization potential.

METHODS

Fresh sperm cells (5 ml of 20 × 10(6)/ml) were co-cultured with SCs layers, derived from prepubertal pig testes or incubated in cell free SC medium or BWW (Biggers, Whitten and Whittingham) medium for 2, 4 or 7 days. Sperm viability, motility, mitochondrial status, DNA fragmentation, chromatin integrity, intracellular calcium and acrosome status were assessed after every co-culture or incubation time, but capacitation and induction of acrosome reaction (AR) with progesterone was only evaluated after 7 days.

RESULTS

SCs layers derived from prepubertal pig testes (co-culture of sperm and SC feeder, CCSCF) were able to preserve normal sperm viability, motility and normal mitochondrial function, after 7 days of culture; CCSCF did not induce AR or hyperactivation of spermatozoa, keeping the sperm in a quiescent state for 7 days of culture. Nevertheless, the sperm were readily able to initiate AR after stimulation with progesterone.

CONCLUSIONS

CCSCF maintained good sperm viability and motility for 7 days. This approach could improve retention of sperm viability and motility during ART procedures and maintain sperm viability, during transfer between two distant Centres, avoiding the need for cryopreservation.

Sperm proteasome and fertilization

The omnipresent ubiquitin–proteasome system (UPS) is an ATP-dependent enzymatic machinery that targets substrate proteins for degradation by the 26S proteasome by tagging them with an isopeptide chain composed of covalently linked molecules of ubiquitin, a small chaperone protein. The current knowledge of UPS involvement in the process of sperm penetration through vitelline coat (VC) during human and animal fertilization is reviewed in this study, with attention also being given to sperm capacitation and acrosome reaction/exocytosis. In ascidians, spermatozoa release ubiquitin-activating and conjugating enzymes, proteasomes, and unconjugated ubiquitin to first ubiquitinate and then degrade the sperm receptor on the VC; in echinoderms and mammals, the VC (zona pellucida/ZP in mammals) is ubiquitinated during oogenesis and the sperm receptor degraded during fertilization. Various proteasomal subunits and associated enzymes have been detected in spermatozoa and localized to sperm acrosome and other sperm structures. By using specific fluorometric substrates, proteasome-specific proteolytic and deubiquitinating activities can be measured in live, intact spermatozoa and in sperm protein extracts. The requirement of proteasomal proteolysis during fertilization has been documented by the application of various proteasome-specific inhibitors and antibodies. A similar effect was achieved by depletion of sperm-surface ATP. Degradation of VC/ZP-associated sperm receptor proteins by sperm-borne proteasomes has been demonstrated in ascidians and sea urchins. On the applied side, polyspermy has been ameliorated by modulating sperm-associated deubiquitinating enzymes. Diagnostic and therapeutic applications could emerge in human reproductive medicine. Altogether, the studies on sperm proteasome indicate that animal fertilization is controlled in part by a unique, gamete associated, extracellular UPS.

Loss of SPEF2 function in mice results in spermatogenesis defects and primary ciliary dyskinesia

Primary ciliary dyskinesia (PCD) results from defects in motile cilia function. Mice homozygous for the mutation big giant head (bgh) have several abnormalities commonly associated with PCD, including hydrocephalus, male infertility, and sinusitis. In the present study, we use a variety of histopathological and cell biological techniques to characterize the bgh phenotype, and we identify the bgh mutation using a positional cloning approach. Histopathological, immunofluorescence, and electron microscopic analyses demonstrate that the male infertility results from shortened flagella and disorganized axonemal and accessory structures in elongating spermatids and mature sperm. In addition, there is a reduced number of elongating spermatids during spermatogenesis and mature sperm in the epididymis. Histological analyses show that the hydrocephalus is characterized by severe dilatation of the lateral ventricles and that bgh sinuses have an accumulation of mucus infiltrated by neutrophils. In contrast to the sperm phenotype, electron microscopy demonstrates that mutant respiratory epithelial cilia are ultrastructurally normal, but video microscopic analysis shows that their beat frequency is lower than that of wild-type cilia. Through a positional cloning approach, we identified two sequence variants in the gene encoding sperm flagellar protein 2 (SPEF2), which has been postulated to play an important role in spermatogenesis and flagellar assembly. A causative nonsense mutation was validated by Western blot analysis, strongly suggesting that the bgh phenotype results from the loss of SPEF2 function. Taken together, the data in this study demonstrate that SPEF2 is required for cilia function and identify a new genetic cause of PCD in mice.

The blood-testis barrier: the junctional permeability, the proteins and the lipids

The elucidation of how individual components of the Sertoli cell junctional complexes form and are dismantled to allow not only individual cells but whole syncytia of germinal cells to migrate from the basal to the lumenal compartment of the seminiferous epithelium without causing a permeability leak in the blood-testis barrier is amongst the most enigmatic yet, challenging and timely questions in testicular physiology. The intriguing key event in this process is how the barrier modulates its permeability during the periods of formation and dismantling of individual Sertoli cell junctions. The purpose of this review is therefore to first provide a reliable account on the normal formation, maintenance and dismantling process of the Sertoli cells junctions, then to assess the influence of the expression of their individual proteins, of the cytoskeleton associated with the junctions, and of the lipid content in the seminiferous tubules on the regulation of the their permeability barrier function. To help focus on the formation and dismantling of the Sertoli cell junctions, several considerations are based on data gleaned not only from rodents but from seasonal breeders as well because these animal models are characterized by exhaustive periods of junction assembly during development and the onset of the seasonal re-initiation of spermatogenesis as well as by an extensive junction dismantling period at the beginning of testicular regression, something unavailable in normal physiological conditions in continual breeders. Thus, the modulation of the permeability barrier function of the Sertoli cell junctions is analyzed in the physiological context of the blood-epidydimis barrier and in particular of the blood-testis barrier rather than in the context of a detailed account of the molecular composition and signalisation pathways of cell junctions. Moreover, the considerations discussed in this review are based on measurements performed on seminiferous tubule-enriched fractions gleaned at regular time intervals during development and the annual reproductive cycle.

Mice lacking the USP2 deubiquitinating enzyme have severe male subfertility associated with defects in fertilization and sperm motility

The ubiquitin-proteasome system plays an important role in spermatogenesis. However, the functions of deubiquitinating enzymes in this process remain poorly characterized. We previously showed that the deubiquitinating enzyme USP2 is induced in late elongating spermatids. To identify its function, we generated mice lacking USP2. Usp2 -/- mice appeared normal, and the weights of major organs, including the testis, did not differ from wild type (Usp2 +/+). However, although the numbers of testicular spermatids and epididymal spermatozoa were normal in Usp2 -/- males, these animals had a severe defect in fertility, yielding only 12% as many offspring as Usp2 +/+ littermates. Spermatogenesis in Usp2 -/- mice was morphologically normal except for the presence of abnormal aggregations of elongating spermatids and formation of multinucleated cells in some tubules. The epididymal epithelium was morphologically normal in Usp2 -/- mice, but some abnormal cells other than sperm were present in the lumen. Usp2 -/- epididymal spermatozoa manifested normal motility when incubated in culture media, but rapidly became immotile when incubated in PBS in contrast to Usp2 +/+ spermatozoa, which largely maintained motility under this condition. Usp2 -/- and +/+ spermatozoa underwent acrosome reactions in vitro with similar frequency. In vitro fertilization assays demonstrated a severe defect in the ability of Usp2 -/- spermatozoa to fertilize eggs. This could be bypassed by intracytoplasmic sperm injection or removal of the zona pellucida, which resulted in fertilization rates similar to that of Usp2 +/+ mice. We demonstrate for the first time, using mouse transgenic approaches, a role for the ubiquitin system in fertilization.

Inhibiting vitamin A metabolism as an approach to male contraception

Although oral contraceptives have been available to women since the 1960s, contraceptive options for men have remained limited. Spermatogenesis relies on the active metabolite of vitamin A, retinoic acid, to drive spermatogonial differentiation and to allow the production of normal numbers of sperm. Recent evidence describes how the enzymes which control vitamin A metabolism in the testis could be targeted to generate effective male contraceptives; however, the detailed mechanism(s) regarding how vitamin A regulates normal spermatogenesis are still unknown. The essential nature of vitamin A to male germ cell development and the prospects of developing the proteins responsible for the generation, transport, and storage of retinoic acid as targets for male contraceptive development are discussed in this review.

Expression of nucleocytoplasmic transport machinery: clues to regulation of spermatogenic development

Spermatogenesis is one example of a developmental process which requires tight control of gene expression to achieve normal growth and sustain function. This review is based on the principle that events in spermatogenesis are controlled by changes in the distribution of proteins between the nuclear and cytoplasmic compartments. Through analysis of the regulated production of nucleocytoplasmic transport machinery in mammalian spermatogenesis, this review addresses the concept that access to the nucleus is tightly controlled to enable and prevent differentiation. A broad review of nuclear transport components is presented, outlining the different categories of machinery required for import, export and non-nuclear functions. In addition, the complexity of nomenclature is addressed by the provision of a concise yet comprehensive listing of information that will aid in comparative studies of different transport proteins and the genes which encode them. We review a suite of existing transcriptional analyses which identify common and distinct patterns of transport machinery expression, showing how these can be linked with key events in spermatogenic development. The additional importance of this for human fertility is considered, in light of data that identify which importin and nuclear transport machinery components are present in testicular cancer specimens, while also providing an indication of how their presence (and absence) may be considered as potential mediators of oncogenesis. This article is part of a Special Issue entitled: Regulation of Signaling and Cellular Fate through Modulation of Nuclear Protein Import.

Desmosomes in the testis: Moving into an unchartered territory

Desmosomes are cell-cell junctions that link to cytoplasmic intermediate filaments, and they are known to mediate robust and stable adhesion in organs such as the skin and heart. Desmosomes are also present between apposing Sertoli cells at the blood-testis barrier, and between Sertoli cells and all germ cells up to, but not including, step 8 spermatids in the seminiferous epithelium. Unfortunately, they remain to be one of the least studied cell junction types in the seminiferous epithelium of the mammalian testis. In this article, we briefly discuss how kinases and the actin cytoskeleton relate to the study of desmosomes in the testis. It is hoped that this information is used to initiate more studies on the biology of the desmosome in the future.