Formation and organization of the mammalian sperm head

Comprehensive analysis of the transcriptome-wide m6A Methylome in sheep testicular development

N6-methyladenosine (m6A) modification of RNA is a critical post-transcriptional modification, that dynamically contributes to testicular development and spermatogenesis. Nevertheless, the investigation into the role of m6A in testicular development of sheep remains insufficient. Herein, we conducted a comprehensive analysis of the m6A transcriptome landscape in the testes of F1 hybrid Southdown × Hu sheep across M0 (0 months old, newborn), M3 (3 months old, sexually immature), M6 (6 months old, sexually mature), and Y1 (1 years old, adult). By profiling the m6A signatures across the transcriptome, we observed distinct differences in m6A modification patterns during sheep testicular development. Our cross-analysis of m6A and mRNA expression revealed that the expression of 743 genes and their m6A modification were concurrent. Notably, the combined analysis of the two comparative groups, M0 vs. M6 and M0 vs. Y1, exhibited a positive correlation, with 30 candidate genes each located within the largest protein-protein interaction network. Intriguingly, eight key hub genes (VEGFA, HDAC9, ZBTB40, KDM5B, MTRR, EAPS1, TSSK3, and BMP4) were identified to be associated with the regulation of sheep testicular development and spermatogenesis. These findings contribute to a deeper understanding of the dynamic role of m6A modification in sheep testicular biology. This study to map RNA m6A modification in sheep testes at different ages, providing novel insights into m6A topology and the molecular mechanisms associated with spermatogenesis in Southdown × Hu sheep F1 hybrids and laying the foundation for further investigations of mammalian spermatogenesis.

Prediction of Nili-Ravi buffalo bull fertility through Fourier harmonic analysis of sperm

Fourier harmonic analysis (FHA) is a robust method for identification of minute changes in sperm nuclear shape that are indicative of reduced fertility. The current study was designed to develop a fertility prediction model for Nili-Ravi buffalo bulls through FHA of sperm. In experiment I, FHA technique was standardized, average sperm nuclear perimeter was measured and sperm nuclear shape plot of buffalo bull was constructed. Sperm of buffalo bulls (n = 10) were stained with YOYO-1 and Hoechst-33342 to differentiate live and dead, and digital images were captured using phase contrast and fluorescent microscopy. The images were analyzed by ImageJ software and 100 sperm/bull were evaluated. The results are described as mean ± SEM values of mean harmonic amplitude (mharm), skewness harmonic amplitude (skharm), kurtosis harmonic amplitude (kurharm) and variance harmonic amplitude (varharm) at Fourier frequencies 0-5 along with the cartesian and polar coordinate plots of buffalo bull sperm. In experiment II, a fertility prediction model was developed based on FHA of buffalo bull sperm. Semen samples of low (n = 6), medium (n = 3) and high (n = 8) fertility bulls were investigated for FHA of sperm and harmonic amplitudes (HA) were generated. Firstly, to determine if live and dead sperm population have unique nuclear shape distribution; the mean, skewness, kurtosis and variance HA 0-5 of 1700 live and 1294 dead spermatozoa of 17 bulls were evaluated. T-test signified a difference in the mharm0 (2.363 ± 0.01 vs. 2.439 ± 0.02), skharm0 (-0.0002 ± 0.07 vs. -0.266 ± 0.09), kurharm0 (-0.156 ± 0.07 vs. 0.260 ± 0.18), kurharm2 (0.142 ± 0.11 vs. 1.031 ± 0.32) and varharm4 (0.109 ± 0.00 vs. 0.082 ± 0.00) of live vs. dead sperm population (p < 0.05). Therefore, 100 live sperm/bull were further evaluated for mean, skewness, kurtosis and variance HA 0-5 values among high (n = 6) and low-fertility (n = 6) groups. Results of T-test showed higher values of mharm2 (0.739 ± 0.01 vs. 0.686 ± 0.00), mharm4 (0.105 ± 0.001 vs. 0.007 ± 0.001), and skharm0 (0.214 ± 0.109 vs. -0.244 ± 0.097) in high vs. low-fertility group (p < 0.05). In next step, five significantly different combinations of discriminant measures between high and low-fertility groups were obtained by discriminant analysis. In conclusion, mharm4, skharm0 and varharm2 correctly identified 91.7 % of bulls into their respective fertility groups, and upon cross validation the value of the canonical correlation was 0.928.

CAMSAP1 role in orchestrating structure and dynamics of manchette microtubule minus-ends impacts male fertility during spermiogenesis

The manchette is a crucial transient structure involved in sperm development, with its composition and regulation still not fully understood. This study focused on investigating the roles of CAMSAP1 and CAMSAP2, microtubule (MT) minus-end binding proteins, in regulating manchette MTs, spermiogenesis, and male fertility. The loss of CAMSAP1, but not CAMSAP2, disrupts the well-orchestrated process of spermiogenesis, leading to abnormal manchette elongation and delayed removal, resulting in deformed sperm nuclei and tails resembling oligoasthenozoospermia symptoms. We investigated the underlying molecular mechanisms by purifying manchette assemblies and comparing them through proteomic analysis, and results showed that the absence of CAMSAP1 disrupted the proper localization of key proteins (CEP170 and KIF2A) at the manchette minus end, compromising its structural integrity and hindering MT depolymerization. These findings highlight the significance of maintaining homeostasis in manchette MT minus-ends for shaping manchette morphology during late spermiogenesis, offering insights into the molecular mechanisms underlying infertility and sperm abnormalities.

Comprehensive Analysis of the Transcriptome-Wide m6A Methylome in Shaziling Pig Testicular Development

RNA N6-methyladenosine (m6A) modification is one of the principal post-transcriptional modifications and plays a dynamic role in testicular development and spermatogenesis. However, the role of m6A in porcine testis is understudied. Here, we performed a comprehensive analysis of the m6A transcriptome-wide profile in Shaziling pig testes at birth, puberty, and maturity. We analyzed the total transcriptome m6A profile and found that the m6A patterns were highly distinct in terms of the modification of the transcriptomes during porcine testis development. We found that key m6A methylated genes (AURKC, OVOL, SOX8, ACVR2A, and SPATA46) were highly enriched during spermatogenesis and identified in spermatogenesis-related KEGG pathways, including Wnt, cAMP, mTOR, AMPK, PI3K-Akt, and spliceosome. Our findings indicated that m6A methylations are involved in the complex yet well-organized post-transcriptional regulation of porcine testicular development and spermatogenesis. We found that the m6A eraser ALKBH5 negatively regulated the proliferation of immature porcine Sertoli cells. Furthermore, we proposed a novel mechanism of m6A modification during testicular development: ALKBH5 regulated the RNA methylation level and gene expression of SOX9 mRNA. In addition to serving as a potential target for improving boar reproduction, our findings contributed to the further understanding of the regulation of m6A modifications in male reproduction.

Ubiquitin Ligase Nrdp1 Controls Autophagy-Associated Acrosome Biogenesis and Mitochondrial Arrangement during Spermiogenesis

Autophagy is critical to acrosome biogenesis and mitochondrial quality control, but the underlying mechanisms remain unclear. The ubiquitin ligase Nrdp1/RNF41 promotes ubiquitination of the mitophagy-associated Parkin and interacts with the pro-autophagic protein SIP/CacyBP. Here, we report that global deletion of Nrdp1 leads to formation of the round-headed sperm and male infertility by disrupting autophagy. Quantitative proteome analyses demonstrated that the expression of many proteins associated with mitochondria, lysosomes, and acrosomes was dysregulated in either spermatids or sperm of the Nrdp1-deficient mice. Deletion of Nrdp1 increased the levels of Parkin but decreased the levels of SIP, the mitochondrial fission protein Drp1 and the mitochondrial protein Tim23 in sperm, accompanied by the inhibition of autophagy, the impairment of acrosome biogenesis and the disruption of mitochondrial arrangement in sperm. Thus, our results uncover an essential role of Nrdp1 in spermiogenesis and male fertility by promoting autophagy, providing important clues to cope with the related male reproductive diseases.

Transcriptome-wide Dynamics of m6A mRNA Methylation During Porcine Spermatogenesis

Spermatogenesis is a continual process that occurs in the testes, in which diploid spermatogonial stem cells (SSCs) differentiate and generate haploid spermatozoa. This highly efficient and intricate process is orchestrated at multiple levels. N6-methyladenosine (m6A), an epigenetic modification prevalent in mRNAs, is implicated in the transcriptional regulation during spermatogenesis. However, the dynamics of m6A modification in non-rodent mammalian species remains unclear. Here, we systematically investigated the profile and role of m6A during spermatogenesis in pigs. By analyzing the transcriptomic distribution of m6A in spermatogonia, spermatocytes, and round spermatids, we identified a globally conserved m6A pattern between porcine and murine genes with spermatogenic function. We found that m6A was enriched in a group of genes that specifically encode the metabolic enzymes and regulators. In addition, transcriptomes in porcine male germ cells could be subjected to the m6A modification. Our data show that m6A plays the regulatory roles during spermatogenesis in pigs, which is similar to that in mice. Illustrations of this point are three genes (SETDB1, FOXO1, and FOXO3) that are crucial to the determination of the fate of SSCs. To the best of our knowledge, this study for the first time uncovers the expression profile and role of m6A during spermatogenesis in large animals and provides insights into the intricate transcriptional regulation underlying the lifelong male fertility in non-rodent mammalian species.

Human globozoospermia-related genes and their role in acrosome biogenesis

The mammalian acrosome is a secretory vesicle attached to the sperm nucleus whose fusion with the overlying plasma membrane is required to achieve fertilization. Acrosome biogenesis starts during meiosis, but it lasts through the entire process of haploid cell differentiation (spermiogenesis). Acrosome biogenesis is a stepwise process that involves membrane traffic from the Golgi apparatus, but it also seems that the lysosome/endosome system participates in this process. Defective sperm head morphology is accompanied by defective acrosome shape and function, and patients with these characteristics are infertile or subfertile. The most extreme case of acrosome biogenesis failure is globozoospermia syndrome, which is primarily characterized by the presence of round-headed spermatozoa without acrosomes with cytoskeleton defects around the nucleus and infertility. Several genes participating in acrosome biogenesis have been uncovered using genetic deletions in mice, but only a few of them have been found to be deleted or modified in patients with globozoospermia. Understanding acrosome biogenesis is crucial to uncovering the molecular basis of male infertility and developing new diagnostic tools and assisted reproductive technologies that may help infertile patients through more effective treatment techniques. This article is categorized under: Reproductive System Diseases > Environmental Factors Infectious Diseases > Stem Cells and Development Reproductive System Diseases > Molecular and Cellular Physiology.

Using publicly available transcriptomic data to identify mechanistic and diagnostic biomarkers in azoospermia and overall male infertility

Azoospermia, which is the absence of spermatozoa in an ejaculate occurring due to defects in sperm production, or the obstruction of the reproductive tract, affects about 1% of all men and is prevalent in up to 10–15% of infertile males. Conventional semen analysis remains the gold standard for diagnosing and treating male infertility; however, advances in molecular biology and bioinformatics now highlight the insufficiency thereof. Hence, the need to widen the scope of investigating the aetiology of male infertility stands pertinent. The current study aimed to identify common differentially expressed genes (DEGs) that might serve as potential biomarkers for non-obstructive azoospermia (NOA) and overall male infertility. DEGs across different datasets of transcriptomic profiling of testis from human patients with different causes of infertility/ impaired spermatogenesis and/or azoospermia were explored using the gene expression omnibus (GEO) database. Following the search using the GEOquery, 30 datasets were available, with 5 meeting the inclusion criteria. The DEGs for datasets were identified using limma R packages through the GEO2R tool. The annotated genes of the probes in each dataset were intersected with DEGs from all other datasets. Enriched Ontology Clustering for the identified genes was performed using Metascape to explore the possible connection or interaction between the genes. Twenty-five DEGs were shared between most of the datasets, which might indicate their role in the pathogenesis of male infertility. Of the 25 DEGs, eight genes (THEG, SPATA20, ROPN1L, GSTF1, TSSK1B, CABS1, ADAD1, RIMBP3) are either involved in the overall spermatogenic processes or at specific phases of spermatogenesis. We hypothesize that alteration in the expression of these genes leads to impaired spermatogenesis and, ultimately, male infertility. Thus, these genes can be used as potential biomarkers for the early detection of NOA.

LINCking the Nuclear Envelope to Sperm Architecture

Nuclear architecture undergoes an extensive remodeling during spermatogenesis, especially at levels of spermatocytes (SPC) and spermatids (SPT). Interestingly, typical events of spermiogenesis, such as nuclear elongation, acrosome biogenesis, and flagellum formation, need a functional cooperation between proteins of the nuclear envelope and acroplaxome/manchette structures. In addition, nuclear envelope plays a key role in chromosome distribution. In this scenario, special attention has been focused on the LINC (linker of nucleoskeleton and cytoskeleton) complex, a nuclear envelope-bridge structure involved in the connection of the nucleoskeleton to the cytoskeleton, governing mechanotransduction. It includes two integral proteins: KASH- and SUN-domain proteins, on the outer (ONM) and inner (INM) nuclear membrane, respectively. The LINC complex is involved in several functions fundamental to the correct development of sperm cells such as head formation and head to tail connection, and, therefore, it seems to be important in determining male fertility. This review provides a global overview of the main LINC complex components, with a special attention to their subcellular localization in sperm cells, their roles in the regulation of sperm morphological maturation, and, lastly, LINC complex alterations associated to male infertility.

Sperm-oocyte interplay: an overview of spermatozoon's role in oocyte activation and current perspectives in diagnosis and fertility treatment

The fertilizing spermatozoon is a highly specialized cell that selects from millions along the female tract until the oocyte. The paternal components influence the oocyte activation during fertilization and are fundamental for normal embryo development; however, the sperm-oocyte interplay is in a continuous debate. This review aims to analyze the available scientific information related to the role of the male gamete in the oocyte activation during fertilization, the process of the interaction of sperm factors with oocyte machinery, and the implications of any alterations in this interplay, as well as the advances and limitations of the reproductive techniques and diagnostic tests. At present, both PLCζ and PAWP are the main candidates as oocyte activated factors during fertilization. While PLCζ mechanism is via IP₃, how PAWP activates the oocyte still no clear, and these findings are important to study and treat fertilization failure due to oocyte activation, especially when one of the causes is the deficiency of PLCζ in the sperm. However, no diagnostic test has been developed to establish the amount of PLCζ, the protocol to treat this type of pathologies is broad, including treatment with ionophores, sperm selection improvement, and microinjection with PLCζ protein or RNA.

Elucidating the Membrane Dynamics and Encapsulation Mechanism of Large DNA Molecules Under Molecular Crowding Conditions Using Giant Unilamellar Vesicles

The conservation throughout evolution of membrane-bound structures that encapsulate genomic material indicates the existence of a simple, physical mechanism that facilitates the enclosing of long-stranded DNA by lipid bilayers. This study aimed to elucidate such a mechanism by investigating how molecular crowding promotes the spontaneous enveloping of model DNA into lipid bilayer membranes. Using fluorescence microscopy and giant unilamellar vesicles (GUVs) we showed that a 166 kb DNA molecule coencapsulated with a model crowder attaches to the inner membrane of the GUVs as they osmotically deflate and after the DNA-membrane complex buds out. The set of results is consistent with the hypothesis that the depletion volume effect is responsible for the spontaneous encapsulation of DNA in the GUVs. This phenomenon may offer novel insights into the basic mechanisms governing membrane encapsulation of long-stranded nucleic acids found in celluar sytems that are independent of genetic control.

Knockout of mouse receptor accessory protein 6 leads to sperm function and morphology defects†

Receptor accessory protein 6 (REEP6) is a member of the REEP/Ypt-interacting protein family that we recently identified as essential for normal endoplasmic reticulum homeostasis and protein trafficking in the retina of mice and humans. Interestingly, in addition to the loss of REEP6 in our knockout (KO) mouse model recapitulating the retinal degeneration of humans with REEP6 mutations causing retinitis pigmentosa (RP), we also found that male mice are sterile. Herein, we characterize the infertility caused by loss of Reep6. Expression of both Reep6 mRNA transcripts is present in the testis; however, isoform 1 becomes overexpressed during spermiogenesis. In vitro fertilization assays reveal that Reep6 KO spermatozoa are able to bind the zona pellucida but are only able to fertilize oocytes lacking the zona pellucida. Although spermatogenesis appears normal in KO mice, cauda epididymal spermatozoa have severe motility defects and variable morphological abnormalities, including bent or absent tails. Immunofluorescent staining reveals that REEP6 expression first appears in stage IV tubules within step 15 spermatids, and REEP6 localizes to the connecting piece, midpiece, and annulus of mature spermatozoa. These data reveal an important role for REEP6 in sperm motility and morphology and is the first reported function for a REEP protein in reproductive processes. Additionally, this work identifies a new gene potentially responsible for human infertility and has implications for patients with RP harboring mutations in REEP6.

Proteomic alterations underlie an association with teratozoospermia in obese mice sperm

BACKGROUND

Obesity is a worldwide crisis impairing human health. In this condition, declines in sperm quality stem from reductions in sperm concentration, motility and increase in sperm deformity. The mechanism underlying these alterations remains largely unknown. This study, determined if obesity-associated proteomic expression patterns in mice sperm parallel those in spermatozoa obtained from obese humans.

METHODS

An obese mouse model was established via feeding a high-fat diet (HFD). Histological analysis identified testicular morphology and a computer assisted semen analyzer (CASA) evaluated sperm parameters. Proteome analysis was performed using a label-free quantitative LC-MS/MS system. Western blot, immunohistochemical and immunofluorescent analyses characterized protein expression levels and localization in testis, sperm and clinical samples.

RESULTS

Bodyweight gains on the HFD induced hepatic steatosis. Declines in sperm motility accompanied sperm deformity development. Differential proteomic analysis identified reduced cytoskeletal proteins, centrosome and spindle pole associated protein 1 (CSPP1) and Centrin 1 (CETN1), in sperm from obese mice. In normal weight mice, both CSPP1 and CETN1 were localized in the spermatocytes and spermatids. Their expression was appreciable in the post-acrosomal region parallel to the microtubule tracks of the manchette structure in spermatids, which affects spermatid head shaping and morphological maintenance. Moreover, CSPP1 was localized in the head-tail coupling apparatus of the mature sperm, while CETN1 expression was delimited to the post-acrosomal region within the sperm head. Importantly, sperm CSPP1 and CETN1 abundance in both the overweight and obese males decreased in comparison with that in normal weight men.

CONCLUSION

These findings show that regionally distinct expression and localization of CETN1 and CSPP1 is strongly related to spermiogenesis and sperm morphology maintaining. Obesity is associated with declines in the CETN1 and CSPP1 abundance and compromise of both sperm morphology in mice and relevant clinical samples. This parallelism between altered protein expression in mice and humans suggests that these effects may contribute to poor sperm quality including increased deformity.

m6A mRNA modification regulates mammalian spermatogenesis

Mammalian spermatogenesis is a highly specialized differentiation process involving precise regulatory mechanisms at the transcriptional, posttranscriptional, and translational levels. Emerging evidence has shown that N⁶-methyladenosine (m⁶A), an epitranscriptomic regulator of gene expression, can influence pre-mRNA splicing, mRNA export, turnover, and translation, which are controlled in the male germline to ensure coordinated gene expression. In this review, we summarize the typical features of m⁶A RNA modification on mRNA during male germline development, and highlight the function of writers, erasers, and readers of m⁶A during mouse spermatogenesis.

Genetic expansion of chaperonin-containing TCP-1 (CCT/TRiC) complex subunits yields testis-specific isoforms required for spermatogenesis in planarian flatworms

Chaperonin-containing Tail-less complex polypeptide 1 (CCT) is a highly conserved, hetero-oligomeric complex that ensures proper folding of actin, tubulin, and regulators of mitosis. Eight subunits (CCT1-8) make up this complex, and every subunit has a homolog expressed in the testes and somatic tissue of the planarian flatworm Schmidtea mediterranea. Gene duplications of four subunits in the genomes of S. mediterranea and other planarian flatworms created paralogs to CCT1, CCT3, CCT4, and CCT8 that are expressed exclusively in the testes. Functional analyses revealed that each CCT subunit expressed in the S. mediterranea soma is essential for homeostatic integrity and survival, whereas sperm elongation defects were observed upon knockdown of each individual testis-specific paralog (Smed-cct1B; Smed-cct3B; Smed-cct4A; and Smed-cct8B), regardless of potential redundancy with paralogs expressed in both testes and soma (Smed-cct1A; Smed-cct3A; Smed-cct4B; and Smed-cct8A). Yet, no detriment was observed in the number of adult somatic stem cells (neoblasts) that maintain differentiated tissue in planarians. Thus, expression of all eight CCT subunits is required to execute the essential functions of the CCT complex. Furthermore, expression of the somatic paralogs in planarian testes is not sufficient to complete spermatogenesis when testis-specific paralogs are knocked down, suggesting that the evolution of chaperonin subunits may drive changes in the development of sperm structure and that correct CCT subunit stoichiometry is crucial for spermiogenesis.

Dynamics of histone H2A, H4 and HS1ph during spermatogenesis with a focus on chromatin condensation and maturity of spermatozoa

Histones and histone phosphorylation play vital roles during animal spermatogenesis and spermatozoa maturation. The dynamic distribution of histones H2A and H4 and phosphorylated H2A and H4 at serine 1 (HS1ph) was explored in mammalian and Decapoda germ cells, with a special focus on the distribution of H2A, H4 and HS1ph between mouse condensed spermatozoa chromatin and crab non-condensed spermatozoa chromatin. The distribution of histone marks was also analysed in mature spermatozoa with different chromatin structures. Histone H2A and H4 marks were closely associated with the relatively loose chromatin structure in crab spermatozoa. The significant decrease in the HS1ph signal during spermatogenesis suggests that eliminating most of these epigenetic marks in the nucleusis closely associated with spermatozoa maturity.

Mfsd14a (Hiat1) gene disruption causes globozoospermia and infertility in male mice

The Mfsd14a gene, previously called Hiat1, encodes a transmembrane protein of unknown function with homology to the solute carrier protein family. To study the function of the MFSD14A protein, mutant mice (Mus musculus, strain 129S6Sv/Ev) were generated with the Mfsd14a gene disrupted with a LacZ reporter gene. Homozygous mutant mice are viable and healthy, but males are sterile due to a 100-fold reduction in the number of spermatozoa in the vas deferens. Male mice have adequate levels of testosterone and show normal copulatory behaviour. The few spermatozoa that are formed show rounded head defects similar to those found in humans with globozoospermia. Spermatogenesis proceeds normally up to the round spermatid stage, but the subsequent structural changes associated with spermiogenesis are severely disrupted with failure of acrosome formation, sperm head condensation and mitochondrial localization to the mid-piece of the sperm. Staining for β-galactosidase activity as a surrogate for Mfsd14a expression indicates expression in Sertoli cells, suggesting that MFSD14A may transport a solute from the bloodstream that is required for spermiogenesis.

Acrosome markers of human sperm

Molecular biomarkers that can assess sperm acrosome status are very useful for evaluating sperm quality in the field of assisted reproductive technology. In this review, we introduce and discuss the localization and function of acrosomal proteins that have been well studied. Journal databases were searched using keywords, including "human acrosome", "localization", "fertilization-related protein", "acrosomal membrane", "acrosomal matrix", "acrosome reaction", "knockout mouse", and "acrosome marker".

The LINC complex component Sun4 plays a crucial role in sperm head formation and fertility

LINC complexes are evolutionarily conserved nuclear envelope bridges, physically connecting the nucleus to the peripheral cytoskeleton. They are pivotal for dynamic cellular and developmental processes, like nuclear migration, anchoring and positioning, meiotic chromosome movements and maintenance of cell polarity and nuclear shape. Active nuclear reshaping is a hallmark of mammalian sperm development and, by transducing cytoskeletal forces to the nuclear envelope, LINC complexes could be vital for sperm head formation as well. We here analyzed in detail the behavior and function of Sun4, a bona fide testis-specific LINC component. We demonstrate that Sun4 is solely expressed in spermatids and there localizes to the posterior nuclear envelope, likely interacting with Sun3/Nesprin1 LINC components. Our study revealed that Sun4 deficiency severely impacts the nucleocytoplasmic junction, leads to mislocalization of other LINC components and interferes with the formation of the microtubule manchette, which finally culminates in a globozoospermia-like phenotype. Together, our study provides direct evidence for a critical role of LINC complexes in mammalian sperm head formation and male fertility.

Mechanisms of spermiogenesis and spermiation and how they are disturbed

Haploid round spermatids undergo a remarkable transformation during spermiogenesis. The nucleus polarizes to one side of the cell as the nucleus condenses and elongates, and the microtubule-based manchette sculpts the nucleus into its species-specific head shape. The assembly of the central component of the sperm flagellum, known as the axoneme, begins early in spermiogenesis, and is followed by the assembly of secondary structures needed for normal flagella. The final remodelling of the mature elongated spermatid occurs during spermiation, when the spermatids line up along the luminal edge, shed their residual cytoplasm and are ultimately released into the lumen. Defects in spermiogenesis and spermiation are manifested as low sperm number, abnormal sperm morphology and poor motility and are commonly observed during reproductive toxicant administration, as well as in genetically modified mouse models of male infertility. This chapter summarizes the major physiological processes and the most commonly observed defects in spermiogenesis and spermiation, to aid in the diagnosis of the potential mechanisms that could be perturbed by experimental manipulation such as reproductive toxicant administration.

Lamin A/C proteins in the spermatid acroplaxome are essential in mouse spermiogenesis

Spermiogenesis is a complex process of terminal differentiation that is necessary to produce mature sperm. Using protein expression profiles of mouse and human testes generated from our previous studies, we chose to examine the actions of lamin A/C in the current investigation. Lamin A and lamin C are isoforms of the A-type lamins that are encoded by theLMNAgene. Our results showed that lamin A/C was expressed in the mouse testis throughout the different stages of spermatogenesis and in mature sperm. Lamin A/C was also expressed in mouse haploid germ cells and was found to be localized to the acroplaxome in spermiogenesis, from round spermatids until mature spermatozoa. The decreased expression of lamin A/C following injections of siRNA againstLmnacaused a significant increase in caudal sperm head abnormalities when compared with negative controls. These abnormalities were characterized by increased fragmentation of the acrosome and abnormal vesicles, which failed to fuse to the developing acrosome. This fragmentation also caused significant alterations in nuclear elongation and acrosome formation. Furthermore, we found that lamin A/C interacted with the microtubule plus-end-tracking protein CLIP170. These results suggest that lamin A/C is critical for proper structural and functional development of the sperm acrosome and head shape.

KATNB1 in the human testis and its genetic variants in fertile and oligoasthenoteratozoospermic infertile men

Oligoasthenoteratozoospermia (OAT) is a phenotype frequently observed in infertile men, and is defined by low spermatozoa number, abnormal spermatozoa morphology and poor motility. We previously showed that a mutation in the Katnb1 gene in mice causes infertility because of OAT. The KATNB1 gene encodes an accessory subunit of the katanin microtubule-severing enzyme complex; this accessory subunit is thought to modulate microtubule-severing location and activity. We hypothesized that KATNB1 may play a role in human spermatogenesis and that genetic variants in KATNB1 could be associated with OAT in humans. Using immunostaining, we defined the localization of the KATNB1 protein in human testes. KATNB1 was present during spermatid development, and in particular localized to the microtubules of the manchette, a structure required for sperm head shaping. To assess a potential association between genetic variants in the KATNB1 gene and infertile men with OAT, we performed direct sequencing of genomic DNA samples from 100 OAT infertile and 100 proven fertile men. Thirty-seven KATNB1 variants were observed, five of which had not previously been described. Ten variants were present only in OAT men, however, statistical analysis did not reveal a significant association with fertility status. Our results suggest that variants in the KATNB1 gene are not commonly associated with OAT infertility in Australian men.

Stallion fertility: a focus on the spermatozoon

Stallion fertility is a vast subject, with a wide array of permutations that can impact reproductive performance in either positive or negative ways. This review is intended to address a mere segment of the male fertility issue, but the very essence of the male contribution to fertilisation, that of the spermatozoon. Spermatozoal ultrastructure and form-to-function are detailed and spermatozoal metabolism is discussed, with specific reference to distinctive characteristics of stallion spermatozoa. Lastly, methods for assessment of spermatozoal function are considered, with emphasis on spermatozoal motility, the acrosome reaction and spermatozoon-oocyte interactions. Closing comments address the need for development and standardisation of molecular-based assays for use with spermatozoa of stallions whose subfertility cannot be explained with conventional tests.

Acute versus chronic loss of mammalian Azi1/Cep131 results in distinct ciliary phenotypes

Defects in cilium and centrosome function result in a spectrum of clinically-related disorders, known as ciliopathies. However, the complex molecular composition of these structures confounds functional dissection of what any individual gene product is doing under normal and disease conditions. As part of an siRNA screen for genes involved in mammalian ciliogenesis, we and others have identified the conserved centrosomal protein Azi1/Cep131 as required for cilia formation, supporting previous Danio rerio and Drosophila melanogaster mutant studies. Acute loss of Azi1 by knock-down in mouse fibroblasts leads to a robust reduction in ciliogenesis, which we rescue by expressing siRNA-resistant Azi1-GFP. Localisation studies show Azi1 localises to centriolar satellites, and traffics along microtubules becoming enriched around the basal body. Azi1 also localises to the transition zone, a structure important for regulating traffic into the ciliary compartment. To study the requirement of Azi1 during development and tissue homeostasis, Azi1 null mice were generated (Azi1^Gt/Gt). Surprisingly, Azi1^Gt/Gt MEFs have no discernible ciliary phenotype and moreover are resistant to Azi1 siRNA knock-down, demonstrating that a compensation mechanism exists to allow ciliogenesis to proceed despite the lack of Azi1. Cilia throughout Azi1 null mice are functionally normal, as embryonic patterning and adult homeostasis are grossly unaffected. However, in the highly specialised sperm flagella, the loss of Azi1 is not compensated, leading to striking microtubule-based trafficking defects in both the manchette and the flagella, resulting in male infertility. Our analysis of Azi1 knock-down (acute loss) versus gene deletion (chronic loss) suggests that Azi1 plays a conserved, but non-essential trafficking role in ciliogenesis. Importantly, our in vivo analysis reveals Azi1 mediates novel trafficking functions necessary for flagellogenesis. Our study highlights the importance of both acute removal of a protein, in addition to mouse knock-out studies, when functionally characterising candidates for human disease.

Cilia are slender projections from the surface of most mammalian cells and have sensory and sometimes motile functions. They are essential for mammalian development and defects in cilia lead to a group of human diseases, termed ciliopathies, with variable symptoms including embryonic lethality, lung and kidney defects, blindness and infertility. Cilia are complex structures composed of hundreds of components, whose individual functions are poorly understood. We screened for mammalian genes important in building cilia, and identified Azi1/Cep131, a gene previously shown to be required for cilia formation and function in fish and flies. We show that if we acutely reduce levels of Azi1 in mouse cells, fewer cells form cilia, but if we generate cells chronically lacking all Azi1, cilia form normally. In addition, mice without any Azi1 are healthy and viable, confirming normal cilia function. However, in these mice, the highly specialised ciliary structure of the sperm tail does not form, resulting in male infertility. We suggest Azi1 has conserved trafficking roles in both primary cilia and the specialised sperm flagella. Abruptly removing Azi1 results in instability causing the existing cilia network to collapse, whereas chronic deletion of Azi1 allows the system to re-equilibrate, and cilia to form normally.

KIF3A is essential for sperm tail formation and manchette function

KIF3A motor protein is responsible for intraflagellar transport, which is required for protein delivery during axoneme formation in ciliated cells. The function of KIF3A during spermatogenesis is not known. In this study, we show that depletion of KIF3A causes severe impairments in sperm tail formation and interestingly, it also affects manchette organization and the shaping of sperm heads. Our results demonstrate the analogy between the mechanisms governing the formation of cilia in somatic cells and the formation of spermatozoa-specific flagella. Furthermore, this study reveals KIF3A as an important regulator of spermatogenesis and emphasizes the crucial role of KIF3A in maintaining male fertility. We also identified several novel interacting partners for KIF3A, including meiosis-specific nuclear structural protein 1 (MNS1) that colocalizes with KIF3A in the manchette and principal piece of the sperm tail. This study highlights the essential role of KIF3A-mediated microtubular transport in the development of spermatozoa and male fertility.

Variational modularity at the cell level: insights from the sperm head of the house mouse

Background

Modularity is an important feature in the evolvability of organisms, since it allows the occurrence of complex adaptations at every single level of biological systems. While at the cellular level the modular organization of molecular interactions has been analyzed in detail, the phenotypic modularity (or variational modularity) of cell shape remains unexplored. The mammalian spermatozoon constitutes one of the most complex and specialized cell types found in organisms. The structural heterogeneity found in the sperm head suggests an association between its inner composition, shape and specificity of function. However, little is known about the extent of the connections between these features. Taking advantage of the house mouse sperm morphology, we analyzed the variational modularity of the sperm head by testing several hypotheses related to its structural and functional organization. Because chromosomal rearrangements can affect the genotype-phenotype map of individuals and thus modify the patterns of covariation between traits, we also evaluate the effect of Robertsonian translocations on the modularity pattern of the sperm head.

Results

The results indicated that the house mouse sperm head is divided into three variational modules (the acrosomal, post-acrosomal and ventral spur module), which correspond to the main regions of the cytoskeletal mesh beneath the plasma membrane, i.e., the perinuclear theca. Most of the covariation is concentrated between the ventral spur and the acrosomal and post-acrosomal modules. Although the Rb fusions did not alter the main modularity pattern, they did affect the percentages of covariation between pairs of modules.

Conclusions

The structural heterogeneity of the cytoskeleton is responsible for the modular organization of the sperm head shape, corroborating the role that this structure has in maintaining the cell shape. The reduction in percentages of shape covariation between pairs of modules in Rb sperms suggests that chromosomal rearrangements could induce changes in the genotype-phenotype map. Nevertheless, how these variations affect sperm fertilization success is yet to be elucidated.

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.

Proteomics of spermatogenesis: from protein lists to understanding the regulation of male fertility and infertility

Proteomic technologies have undergone significant development in recent years, which has led to extensive advances in protein research. Currently, proteomic approaches have been applied to many scientific areas, including basic research, various disease and malignant tumour diagnostics, biomarker discovery and other therapeutic applications. In addition, proteomics-driven research articles examining reproductive biology and medicine are becoming increasingly common. The key challenge for this field is to move from lists of identified proteins to obtaining biological information regarding protein function. The present article reviews the available scientific literature related to spermatogenesis. In addition, this study uses two-dimensional electrophoresis mass spectrometry (2DE-MS) and liquid chromatography (LC)-MS to construct a series of proteome profiles describing spermatogenesis. This large-scale identification of proteins provides a rich resource for elucidating the mechanisms underlying male fertility and infertility.

Extraordinary sequence divergence at Tsga8, an X-linked gene involved in mouse spermiogenesis

The X chromosome plays an important role in both adaptive evolution and speciation. We used a molecular evolutionary screen of X-linked genes potentially involved in reproductive isolation in mice to identify putative targets of recurrent positive selection. We then sequenced five very rapidly evolving genes within and between several closely related species of mice in the genus Mus. All five genes were involved in male reproduction and four of the genes showed evidence of recurrent positive selection. The most remarkable evolutionary patterns were found at Testis-specific gene a8 (Tsga8), a spermatogenesis-specific gene expressed during postmeiotic chromatin condensation and nuclear transformation. Tsga8 was characterized by extremely high levels of insertion-deletion variation of an alanine-rich repetitive motif in natural populations of Mus domesticus and M. musculus, differing in length from the reference mouse genome by up to 89 amino acids (27% of the total protein length). This population-level variation was coupled with striking divergence in protein sequence and length between closely related mouse species. Although no clear orthologs had previously been described for Tsga8 in other mammalian species, we have identified a highly divergent hypothetical gene on the rat X chromosome that shares clear orthology with the 5' and 3' ends of Tsga8. Further inspection of this ortholog verified that it is expressed in rat testis and shares remarkable similarity with mouse Tsga8 across several general features of the protein sequence despite no conservation of nucleotide sequence across over 60% of the rat-coding domain. Overall, Tsga8 appears to be one of the most rapidly evolving genes to have been described in rodents. We discuss the potential evolutionary causes and functional implications of this extraordinary divergence and the possible contribution of Tsga8 and the other four genes we examined to reproductive isolation in mice.

KIFC1-like motor protein associates with the cephalopod manchette and participates in sperm nuclear morphogenesis in Octopus tankahkeei

Background

Nuclear morphogenesis is one of the most fundamental cellular transformations taking place during spermatogenesis. In rodents, a microtubule-based perinuclear structure, the manchette, and a C-terminal kinesin motor KIFC1 are believed to play crucial roles in this process. Spermatogenesis in Octopus tankahkeei is a good model system to explore whether evolution has created a cephalopod prototype of mammalian manchette-based and KIFC1-dependent sperm nuclear shaping machinery.

Methodology/Principal Findings

We detected the presence of a KIFC1-like protein in the testis, muscle, and liver of O. tankahkeei by Western Blot. Then we tracked its dynamic localization in spermatic cells at various stages using Immunofluorescence and Immunogold Electron Microscopy. The KIFC1-like protein was not expressed at early stages of spermatogenesis when no significant morphological changes occur, began to be present in early spermatid, localized around and in the nucleus of intermediate and late spermatids where the nucleus was dramatically elongated and compressed, and concentrated at one end of final spermatid. Furthermore, distribution of the motor protein during nuclear elongation and condensation overlapped with that of the cephalopod counterpart of manchette at a significant level.

Conclusions/Significance

The results support the assumption that the protein is actively involved in sperm nuclear morphogenesis in O. tankahkeei possibly through bridging the manchette-like perinuclear microtubules to the nucleus and assisting in the nucleocytoplasmic trafficking of specific cargoes. This study represents the first description of the role of a motor protein in sperm nuclear shaping in cephalopod.

Mammalian sperm head formation involves different polarization of two novel LINC complexes

BACKGROUND

LINC complexes are nuclear envelope bridging protein structures formed by interaction of SUN and KASH proteins. They physically connect the nucleus with the peripheral cytoskeleton and are critically involved in a variety of dynamic processes, such as nuclear anchorage, movement and positioning and meiotic chromosome dynamics. Moreover, they are shown to be essential for maintaining nuclear shape.

FINDINGS

Based on detailed expression analysis and biochemical approaches, we show here that during mouse sperm development, a terminal cell differentiation process characterized by profound morphogenic restructuring, two novel distinctive LINC complexes are established. They consist either of spermiogenesis-specific Sun3 and Nesprin1 or Sun1eta, a novel non-nuclear Sun1 isoform, and Nesprin3. We could find that these two LINC complexes specifically polarize to opposite spermatid poles likely linking to sperm-specific cytoskeletal structures. Although, as shown in co-transfection/immunoprecipitation experiments, SUN proteins appear to arbitrarily interact with various KASH partners, our study demonstrates that they actually are able to confine their binding to form distinct LINC complexes.

CONCLUSIONS

Formation of the mammalian sperm head involves assembly and different polarization of two novel spermiogenesis-specific LINC complexes. Together, our findings suggest that theses LINC complexes connect the differentiating spermatid nucleus to surrounding cytoskeletal structures to enable its well-directed shaping and elongation, which in turn is a critical parameter for male fertility.

Proteomic analysis of proteins involved in spermiogenesis in mouse

Spermiogenesis is a unique process in mammals during which haploid round spermatids mature into spermatozoa in the testis. Its successful completion is necessary for fertilization and its malfunction is an important cause of male infertility. Here, we report the high-confidence identification of 2116 proteins in mouse haploid germ cells undergoing spermiogenesis: 299 of these were testis-specific and 155 were novel. Analysis of these proteins showed many proteins possibly functioning in unique processes of spermiogenesis. Of the 84 proteins annotated to be involved in vesicle-related events, VAMP4 was shown to be important for acrosome biogenesis by in vivo knockdown experiments. Knockdown of VAMP4 caused defects of acrosomal vesicle fusion and significantly increased head abnormalities in spermatids from testis and sperm from the cauda epididymis. Analysis of chromosomal distribution of the haploid genes showed underrepresentation on the X chromosome and overrepresentation on chromosome 11, which were due to meiotic sex chromosome inactivation and expansion of testis-expressed gene families, respectively. Comparison with transcriptional data showed translational regulation during spermiogenesis. This characterization of proteins involved in spermiogenesis provides an inventory of proteins useful for understanding the mechanisms of male infertility and may provide candidates for drug targets for male contraception and male infertility.

Loss of protein phosphatase 1c{gamma} (PPP1CC) leads to impaired spermatogenesis associated with defects in chromatin condensation and acrosome development: an ultrastructural analysis

Human male infertility affects approximately 5% of men, with one-third suffering from testicular failure, likely the result of an underlying genetic abnormality that disrupts spermatogenesis during development. Mouse models of male infertility such as the Ppp1cc knockout mouse display very similar phenotypes to humans with testicular failure. Male Ppp1cc mutant mice are sterile due to disruptions in spermatogenesis that begin during prepubertal testicular development, and continue into adulthood, often resulting in loss of germ cells to the point of Sertoli cell-only syndrome. The current study employs light and electron microscopy to identify new morphological abnormalities in Ppp1cc mutant seminiferous epithelium. This study reveals that germ cells become delayed in their development around stages VII and VIII of spermatogenesis. Loss of these cells likely results in the reduced numbers of elongating spermatids and spermatozoa previously observed in mutant animals. Interestingly, Ppp1cc mutants also display reduced numbers of spermatogonia compared with their wild-type counterparts. Using electron microscopy, we have shown that junction complexes in Ppp1cc mutants are ultrastructurally normal, and therefore do not contribute to the breakdown in tissue architecture seen in mutants. Electron microscopy revealed major acrosomal and chromatin condensation defects in Ppp1cc mutants. Our observations are discussed in the context of known molecular changes in Ppp1cc mutant testes.

Immunohistochemical study of nuclear changes associated with male germ cell death and spermiogenesis

In a previous study on the effects of gestational and lactational exposure of para-nonylphenol on male rats, we noted in both induced and uninduced rats, that variations in cleaved caspase-3 immunostaining patterns were associated with distinct nuclear alterations in mainly basally located germ cells (spermatogonia and preleptotene spermatocytes). These were re-analysed and compared with cleaved caspase-3-labeled germ cells in the aging human and the spermatogenically active catfish testis. In the rat testes, cytoplasmic immunostaining was progressively associated with lateral compression of the nucleus, its break up into large pieces which can contain immunostained marginated chromatin masses. The pale remnants of the nucleus continued to shrink in size concomitant with the appearance of blue-purplish stained regions in the cytoplasm similar in color to the condensed chromatin in spermatids, a condition which was TUNEL-negative. These large clumps of chromatin also eventually disappeared, giving rise to cells resembling cytoplasmic ghosts, a condition which was TUNEL-positive. By contrast, the immunolabeled nuclei of human and catfish germ cells condensed into a single mass, after which they lost immunoreactivity. To exclude the possibility that these observations could reflect alterations in Sertoli nuclei, rat testicular sections were probed with a mouse anti-human GATA-4 monoclonal (MHM) antibody. The MHM was, however, the second of two GATA-4 antibodies tested, with a goat anti-mouse polyclonal (GMP) initially used to label the rat Sertoli nuclei. GMP unexpectedly, but distinctly labeled the complete development of the acrosome in the rat testis, a fortuitous finding with utility for staging of the seminiferous epithelium.

Phenotyping male infertility in the mouse: how to get the most out of a 'non-performer'

BACKGROUND

Functional male gametes are produced through complex processes that take place within the testis, epididymis and female reproductive tract. A breakdown at any of these phases can result in male infertility. The production of mutant mouse models often yields an unexpected male infertility phenotype. It is with this in mind that the current review has been written. The review aims to act as a guide to the ‘non-reproductive biologist’ to facilitate a systematic analysis of sterile or subfertile mice and to assist in extracting the maximum amount of information from each model.

METHODS

This is a review of the original literature on defects in the processes that take a mouse spermatogonial stem cell through to a fully functional spermatozoon, which result in male infertility. Based on literature searches and personal experience, we have outlined a step-by-step strategy for the analysis of an infertile male mouse line.

RESULTS

A wide range of methods can be used to define the phenotype of an infertile male mouse. These methods range from histological methods such as electron microscopy and immunohistochemistry, to hormone analyses and methods to assess sperm maturation status and functional competence.

CONCLUSION

With the increased rate of genetically modified mouse production, the generation of mouse models with unexpected male infertility is increasing. This manuscript will help to ensure that the maximum amount of information is obtained from each mouse model and, by extension, will facilitate the knowledge of both normal fertility processes and the causes of human infertility.

RIM-BP3 is a manchette-associated protein essential for spermiogenesis

During spermiogenesis, round spermatids are converted into motile sperm in mammals. The mechanisms responsible for sperm morphogenesis are poorly understood. We have characterized a novel protein, RIM-BP3, with a specialized function in spermatid development in mice. The RIM-BP3 protein is associated with the manchette, a transient microtubular structure believed to be important for morphogenesis during spermiogenesis. Targeted deletion of the RIM-BP3 gene resulted in male infertility owing to abnormal sperm heads, which are characterized by a deformed nucleus and a detached acrosome. Consistent with its role in morphogenesis, the RIM-BP3 protein physically associates with Hook1, a known manchette-bound protein required for sperm head morphogenesis. Interestingly, RIM-BP3 does not interact with the truncated Hook1 protein characterized in azh (abnormal spermatozoon head) mutant mice. Moreover, RIM-BP3 and Hook1 mutant mice display several common abnormalities, in particular with regard to the ectopic positioning of the manchette within the spermatid, a presumed cause of sperm head deformities. These observations suggest an essential role for RIM-BP3 in manchette development and function through its interaction with Hook1. As the occurrence of deformed spermatids is one of the common abnormalities leading to malfunctional sperm, identification of RIM-BP3 might provide insight into the molecular cue underlying causes of male infertility in humans.

Intramanchette transport during primate spermiogenesis: expression of dynein, myosin Va, motor recruiter myosin Va, VIIa-Rab27a/b interacting protein, and Rab27b in the manchette during human and monkey spermiogenesis

AIM

To show whether molecular motor dynein on a microtubule track, molecular motor myosin Va, motor recruiter myosin Va, VIIa-Rab27a/b interacting protein (MyRIP), and vesicle receptor Rab27b on an F-actin track were present during human and monkey spermiogenesis involving intramanchette transport (IMT).

METHODS

Spermiogenic cells were obtained from three men with obstructive azoospermia and normal adult cynomolgus monkey (Macaca fascicularis). Immunocytochemical detection and reverse transcription-polymerase chain reaction (RT-PCR) analysis of the proteins were carried out. Samples were analyzed by light microscope.

RESULTS

Using RT-PCR, we found that dynein, myosin Va, MyRIP and Rab27b were expressed in monkey testis. These proteins were localized to the manchette, as shown by immunofluorescence, particularly during human and monkey spermiogenesis.

CONCLUSION

We speculate that during primate spermiogenesis, those proteins that compose microtubule-based and actin-based vesicle transport systems are actually present in the manchette and might possibly be involved in intramanchette transport.

Vezatin, a ubiquitous protein of adherens cell-cell junctions, is exclusively expressed in germ cells in mouse testis

In the male reproductive organs of mammals, the formation of spermatozoa takes place during two successive phases: differentiation (in the testis) and maturation (in the epididymis). The first phase, spermiogenesis, relies on a unique adherens junction, the apical ectoplasmic specialization linking the epithelial Sertoli cells to immature differentiating spermatids. Vezatin is a transmembrane protein associated with adherens junctions and the actin cytoskeleton in most epithelial cells. We report here the expression profile of vezatin during spermatogenesis. Vezatin is exclusively expressed in haploid germ cells. Immunocytochemical and ultrastructural analyses showed that vezatin intimately coincides, temporally and spatially, with acrosome formation. While vezatin is a transmembrane protein associated with adherens junctions in many epithelial cells, it is not seen at the ectoplasmic specializations, neither at the basal nor at the apical sites, in the seminiferous epithelium. In particular, vezatin does not colocalize with espin and myosin VIIa, two molecular markers of the ectoplasmic specialization. In differentiating spermatids, ultrastructural data indicate that vezatin localizes in the acrosome. In epididymal sperm, vezatin localizes also to the outer acrosomal membrane. Considering its developmental and molecular characteristics, vezatin may be involved in the assembly/stability of this spermatic membrane.

Evolutionary diversification of SPANX-N sperm protein gene structure and expression

The sperm protein associated with nucleus in the X chromosome (SPANX) genes cluster at Xq27 in two subfamilies, SPANX-A/D and SPANX-N. SPANX-A/D is specific for hominoids and is fairly well characterized. The SPANX-N gave rise to SPANX-A/D in the hominoid lineage ∼7 MYA. Given the proposed role of SPANX genes in spermatogenesis, we have extended studies to SPANX-N gene evolution, variation, regulation of expression, and intra-sperm localization. By immunofluorescence analysis, SPANX-N proteins are localized in post-meiotic spermatids exclusively, like SPANX-A/D. But in contrast to SPANX-A/D, SPANX-N are found in all ejaculated spermatozoa rather than only in a subpopulation, are localized in the acrosome rather than in the nuclear envelope, and are expressed at a low level in several nongametogenic adult tissues as well as many cancers. Presence of a binding site for CTCF and its testis-specific paralogue BORIS in the SPANX promoters suggests, by analogy to MAGE-A1 and NY-ESO-1, that their activation in spermatogenesis is mediated by the programmed replacement of CTCF by BORIS. Based on the relative density of CpG, the more extended expression of SPANX-N compared to SPANX-A/D in nongametogenic tissues is likely attributed to differences in promoter methylation. Our findings suggest that the recent duplication of SPANX genes in hominoids was accompanied by different localization of SPANX-N proteins in post-meiotic sperm and additional expression in several nongonadal tissues. This suggests a corresponding functional diversification of SPANX gene families in hominoids. SPANX proteins thus provide unique targets to investigate their roles in the function of spermatozoa, selected malignancies, and for SPANX-N, in other tissues as well.

Factors maintaining normal sperm tail structure during epididymal maturation studied in Gopc-/- mice

Gopc (Golgi-associated PDZ- and coiled-coil motif-containing protein)(-/-) mice are infertile, showing globozoospermia, coiled tails, and a stratified mitochondrial sheath. Transmission electron microscope (TEM) images of the spermatozoa were studied quantitatively to analyze disorganization processes during epididymal passage. Factors maintaining straight tail and normal mitochondrial sheath were also studied by TEM and immunofluorescent microscopy. Sperm tails retained a normal appearance in the proximal caput epididymidis. Tail disorganization started between the proximal and the middle caput epididymidis, and the latter is the major site for it. The tail moved up through the defective posterior ring and coiled around the nucleus to various degrees. Tail coiling occurred in the caput epididymidis suggesting it was triggered by cytoplasmic droplet migration. SPATA19/spergen-1, a candidate mitochondrial adhesion protein, remained on the stratified mitochondria, while GPX4/PHGPx, a major element of the mitochondrial capsule, was unevenly distributed on them. From these findings, we speculate GPX4 is necessary to maintain normal sheath structure, and SPATA19 prevents dispersal of mitochondria, resulting in a stratified mitochondrial sheath formation in Gopc(-/-) spermatozoa. The epididymal epithelium was normal in structure and LRP8/apoER2 expression suggesting that tail abnormality is due to intrinsic sperm factors. Three cell structures are discussed as requisite factors for maintaining a straight tail during epididymal maturation: 1) a complete posterior ring to prevent invasion of the tail into the head compartment, 2) stable attachment of the connecting piece to the implantation fossa, and 3) a normal mitochondrial sheath supported by SPATA19 and supplied with sufficient and normally distributed GPX4.

Coxsackievirus and adenovirus receptor (CAR) is expressed in male germ cells and forms a complex with the differentiation factor JAM-C in mouse testis

The coxsackievirus and adenovirus receptor (CAR) is a transmembrane protein important for viral binding to target cells. Using RT-PCR, Western analysis, GST pull-down assay and indirect immunofluorescence, it was shown that CAR is expressed in male germ cells from mice, rats, and humans. CAR was detected in round spermatids in the testis as well as in purified, mature spermatozoa. The two membrane-bound isoforms of CAR occupied different subcellular sites in the acrosomal region of the spermatozoa. CAR was exposed on the surface of acrosome-reacted, but not acrosome-intact cells. Two CAR-binding proteins belonging to the ligand-of-numb protein-X (LNX) family also occupied distinct regions in spermatozoa. Finally, co-immunoprecipitation experiments demonstrated an interaction between CAR and JAM-C, a protein required for spermatid differentiation. Together, these findings imply a function for CAR in male fertility. The results also suggest that CAR in spermatozoa is inaccessible to adenovirus-based gene therapy vectors, and that the risk of germ line infection therefore is low.