Gcn5-Mediated Histone Acetylation Governs Nucleosome Dynamics in Spermiogenesis

During mammalian spermatogenesis, germ cell chromatin undergoes dramatic histone acetylation-mediated reorganization, whereby 90%-99% of histones are evicted. Given the potential role of retained histones in fertility and embryonic development, the genomic location of retained nucleosomes is of great interest. However, the ultimate position and mechanisms underlying nucleosome eviction or retention are poorly understood, including several studies utilizing micrococcal-nuclease sequencing (MNase-seq) methodologies reporting remarkably dissimilar locations. We utilized assay for transposase accessible chromatin sequencing (ATAC-seq) in mouse sperm and found nucleosome enrichment at promoters but also retention at inter- and intragenic regions and repetitive elements. We further generated germ-cell-specific, conditional knockout mice for the key histone acetyltransferase Gcn5, which resulted in abnormal chromatin dynamics leading to increased sperm histone retention and severe reproductive phenotypes. Our findings demonstrate that Gcn5-mediated histone acetylation promotes chromatin accessibility and nucleosome eviction in spermiogenesis and that loss of histone acetylation leads to defects that disrupt male fertility and potentially early embryogenesis.

Testicular Structure and Spermatogenesis in the Naked Mole-Rat Is Unique (Degenerate) and Atypical Compared to Other Mammals

The naked mole-rat (NMR) queen controls reproduction in her eusocial colony by usually selecting one male for reproduction and suppressing gametogenesis in all other males and females. Simplified, polymorphic and slow-swimming spermatozoa in the NMR seem to have been shaped by a low risk of sperm competition. We hypothesize that this unique mammalian social organization has had a dramatic influence on testicular features and spermatogenesis in the NMR. The testicular structure as well as spermatogenic cell types and its organization in breeding, subordinate and disperser males were studied using light microscopy and transmission electron microscopy. Even though the basic testicular design in NMRs is similar to most Afrotheria as well as some rodents with intra-abdominal testes, the Sertoli and spermatogenic cells have many atypical mammalian features. Seminiferous tubules are distended and contain large volumes of fluid while interstitial tissue cover about 50% of the testicular surface area and is mainly composed of Leydig cells. The Sertoli cell cytoplasm contains an extensive network of membranes and a variety of fluid-containing vesicles. Furthermore, Sertoli cells form numerous phagosomes that often appear as extensive accumulations of myelin. Another unusual feature of mature NMR Sertoli cells is mitotic division. While the main types of spermatogonia and spermatocytes are clearly identifiable, these cells are poorly organized and many spermatids without typical intercellular bridges are present. Spermatid heads appear to be malformed with disorganized chromatin, nuclear fragmentation and an ill-defined acrosome formed from star-like Golgi bodies. Rudimentary manchette development corresponds with the occurrence of abnormal sperm morphology. We also hypothesize that NMR testicular organization and spermiation are modified to produce spermatozoa on demand in a short period of time and subsequently use a Sertoli cell "pump" to flush the spermatozoa into short tubuli recti and simplified rete testis. Despite the difficulty in finding cellular associations during spermatogenesis, six spermatogenic stages could be described in the NMR. These numerous atypical and often simplified features of the NMR further supports the notion of degenerative orthogenesis that was selected for due to the absence of sperm competition.

Essential Role of Histone Replacement and Modifications in Male Fertility

Spermiogenesis is a complex cellular differentiation process that the germ cells undergo a distinct morphological change, and the protamines replace the core histones to facilitate chromatin compaction in the sperm head. Recent studies show the essential roles of epigenetic events during the histone-to-protamine transition. Defects in either the replacement or the modification of histones might cause male infertility with azoospermia, oligospermia or teratozoospermia. Here, we summarize recent advances in our knowledge of how epigenetic regulators, such as histone variants, histone modification and their related chromatin remodelers, facilitate the histone-to-protamine transition during spermiogenesis. Understanding the molecular mechanism underlying the modification and replacement of histones during spermiogenesis will enable the identification of epigenetic biomarkers of male infertility, and shed light on potential therapies for these patients in the future.

Two novel ligand-independent variants of the VEGFR-1 receptor are expressed in human testis and spermatozoa, one of them with the ability to activate SRC proto-oncogene tyrosine kinases

The vascular endothelial growth factor receptor 1 (VEGFR-1) family of receptors is preferentially expressed in endothelial cells, with the full-length and mostly the soluble (sVEGFR-1) isoforms being the most expressed ones. Surprisingly, cancer cells (MDA-MB-231) express, instead, alternative intracellular VEGFR-1 variants. We wondered if these variants, that are no longer dependent on ligands for activation, were expressed in a physiological context, specifically in spermatogenic cells, and whether their expression was maintained in spermatozoa and required for human fertility. By interrogating a human library of mature testis cDNA, we characterized two new truncated intracellular variants different from the ones previously described in cancer cells. The new isoforms were transcribed from alternative transcription start sites (aTSS) located respectively in intron-19 (i₁₉VEGFR-1) and intron-28 (i₂₈VEGFR-1) of the VEGFR-1 gene (GenBank accession numbers JF509744 and JF509745) and expressed in mature testis and spermatozoa. In this paper, we describe the characterization of these isoforms by RT-PCR, northern blot, and western blot, their preferential expression in human mature testis and spermatozoa, and the elements that punctuate their proximal promoters and suggest cues for their expression in spermatogenic cells. Mechanistically, we show that i₁₉VEGFR-1 has a strong ability to phosphorylate and activate SRC proto-oncogene non-receptor tyrosine kinases and a significant bias toward a decrease in expression in patients considered infertile by WHO criteria.

Mechanism of Acrosome Biogenesis in Mammals

During sexual reproduction, two haploid gametes fuse to form the zygote, and the acrosome is essential to this fusion process (fertilization) in animals. The acrosome is a special kind of organelle with a cap-like structure that covers the anterior portion of the head of the spermatozoon. The acrosome is derived from the Golgi apparatus and contains digestive enzymes. With the progress of our understanding of acrosome biogenesis, a number of models have been proposed to address the origin of the acrosome. The acrosome has been regarded as a lysosome-related organelle, and it has been proposed to have originated from the lysosome or the autolysosome. Our review will provide a brief historical overview and highlight recent findings on acrosome biogenesis in mammals.

CCDC42 Localizes to Manchette, HTCA and Tail and Interacts With ODF1 and ODF2 in the Formation of the Male Germ Cell Cytoskeleton

Terminal differentiation of male germ cells into functional spermatozoa requires shaping and condensation of the nucleus as well as the formation of sperm-specific structures. A transient microtubular structure, the manchette, is mandatory for sperm head shaping and the development of the connecting piece and the sperm tail. The connecting piece or head-to-tail coupling apparatus (HTCA) mediates the tight linkage of sperm head and tail causing decapitation and infertility when faulty. Using mice as the experimental model, several proteins have already been identified affecting the linkage complex, manchette or tail formation when missing. However, our current knowledge is far too rudimentary to even draft an interacting protein network. Depletion of the major outer dense fiber protein 1 (ODF1) mainly caused decapitation and male infertility but validated binding partners collaborating in the formation of sperm-specific structures are largely unknown. Amongst all candidate proteins affecting the HTCA when missing, the structural protein CCDC42 attracted our attention. The coiled-coil domain containing 42 (CCDC42) is important for HTCA and sperm tail formation but is otherwise largely uncharacterized. We show here that CCDC42 is expressed in spermatids and localizes to the manchette, the connecting piece and the tail. Beyond that, we show that CCDC42 is not restricted to male germ cells but is also expressed in somatic cells in which it localizes to the centrosome. Although centrosomal and sperm tail location seems to be irrespective of ODF1 we asked whether both proteins may form an interacting network in the male germ cell. We additionally considered ODF2, a prevalent protein involved in the formation of spermatid-specific cytoskeletal structures, as a putative binding partner. Our data depict for the first time the subcellular location of CCDC42 in spermatids and deepen our knowledge about the composition of the spermatid/sperm-specific structures. The presence of CCDC42 in the centrosome of somatic cells together with the obvious restricted male-specific phenotype when missing strongly argues for a compensatory function by other still unknown proteins most likely of the same family.

[CMTM2 is involved in spermiogenesis in mice]

OBJECTIVE

To investigate whether CKLF-like MARVEL transmembrane domain-containing protein 2 (CMTM2) is involved in spermatogenesis in mice. CMTM2 is highly expressed in testis, and could possibly be a potential spermagogenesis specific gene.

METHODS

CMTM2-deficient mouse model was generated. Northern, RT-PCR and Western blotting analysis were performed on total RNA derived from wild-type (WT, CMTM2+/+) and CMTM2+/- (heterozygote) and CMTM2-/-(homozygote) mice to examine the CMTM2 level. The number of litters and the number of pups were counted and pregnancy rates calculated. The motility and morphology of the sperm and the histology of testes were analyzed. Serum testosterone and FSH concentrations were also measured. Standard t-tests were used and standard error of means were calculated.

RESULTS

CMTM2 was highly expressed in a finely regulated pattern in the mouse testis during spermatogenesis. The body weight of adult mice with CMTM2 deficiency was not significantly different from that of wild type mice. No obvious anatomical or behavioral abnormalities were observed. The testis of CMTM2-/- was smaller than that of CMTM2+/+ mice. The testis diameter in wild mice and CMTM2 null mice were (11.32±1.21) mm vs. (8.29±1.92) mm (P<0.05), and the weights were (101.63±2.33) mg vs. (85.22±2.84) mg (P<0.05), respectively. Female CMTM2 null mice were fertile, indicating that CMTM2 was not required for female gametogenesis. The CMTM2-/- mice produced virtually no sperm, and CMTM2+/- mice sperm count showed a significant decline. In terms of sperm morphorlogy study, more round spermatids could be observed in the heterozygote group, compared with the wild type group; while in the homozygote group, a large amount of round spermatids could be observed because of complete arrest of spermiogenesis. The hormone levels were not significantly different. The CMTM2-/- male mice were sterile due to a late, complete arrest of spermiogenesis. The organized architecture of the seminiferous epithelium of the seminiferous tubules seen in CMTM2+/+ mice was lost in CMTM2-/- mice.

CONCLUSION

This study suggests CMTM2 is not required for embryonic development in the mouse but is essential for spermiogenesis, however, further studies are required for more detailed mechanism study.

The Protein Phosphorylation Landscape of Mouse Spermatids during Spermiogenesis

The characteristic tadpole shape of sperm is formed from round spermatids via spermiogenesis, a process which results in dramatic morphological changes in the final stage of spermatogenesis in the testis. Protein phosphorylation, as one of the most important post-translational modifications, can regulate spermiogenesis; however, the phosphorylation events taking place during this process have not been systematically analyzed. In order to better understand the role of phosphorylation in spermiogenesis, large-scale phosphoproteome profiling is performed using IMAC and TiO₂ enrichment. In total, 13 835 phosphorylation sites, in 4196 phosphoproteins, are identified in purified mouse spermatids undergoing spermiogenesis in two biological replicates. Overall, 735 testis-specific proteins are identified to be phosphorylated, and are expressed at high levels during spermiogenesis. Gene ontology analysis shows enrichment of the identified phosphoproteins in terms of histone modification, cilium organization, centrosome and the adherens junction. Further characterization of the kinase-substrate phosphorylation network demonstrates enrichment of phosphorylation substrates related to the regulation of spermiogenesis. This global protein phosphorylation landscape of spermiogenesis shows wide phosphoregulation across a diverse range of processes during spermiogenesis and can help to further characterize the process of sperm generation. All MS data are available via ProteomeXchange with the identifier PXD011890.

Testis-Specific SEPT12 Expression Affects SUN Protein Localization and is Involved in Mammalian Spermiogenesis

Male infertility is observed in approximately 50% of all couples with infertility. Intracytoplasmic sperm injection (ICSI), a conventional artificial reproductive technique for treating male infertility, may fail because of a severe low sperm count, immotile sperm, immature sperm, and sperm with structural defects and DNA damage. Our previous studies have revealed that mutations in the septin (SEPT)-coding gene SEPT12 cause teratozoospermia and severe oligozoospermia. These spermatozoa exhibit morphological defects in the head and tail, premature chromosomal condensation, and nuclear damage. Sperm from Sept12 knockout mice also cause the developmental arrest of preimplantation embryos generated through in vitro fertilization and ICSI. Furthermore, we found that SEPT12 interacts with SPAG4, a spermatid nuclear membrane protein that is also named SUN4. Loss of the Spag4 allele in mice also disrupts the integration nuclear envelope and reveals sperm head defects. However, whether SEPT12 affects SPAG4 during mammalian spermiogenesis remains unclear. We thus conducted this study to explore this question. First, we found that SPAG4 and SEPT12 exhibited similar localizations in the postacrosomal region of elongating spermatids and at the neck of mature sperm through isolated murine male germ cells. Second, SEPT12 expression altered the nuclear membrane localization of SPAG4, as observed through confocal microscopy, in a human testicular cancer cell line. Third, SEPT12 expression also altered the localizations of nuclear membrane proteins: LAMINA/C in the cells. This effect was specifically due to the expression of SEPT12 and not that of SEPT1, SEPT6, SEPT7, or SEPT11. Based on these results, we suggest that SEPT12 is among the moderators of SPAG4/LAMIN complexes and is involved in the morphological formation of sperm during mammalian spermiogenesis.

Proteinase K is an activator for the male-dependent spermiogenesis pathway in Caenorhabditis elegans: Its application to pharmacological dissection of spermiogenesis

Caenorhabditis elegans spermiogenesis involves spermatid activation into spermatozoa. Activation occurs through either SPE-8 class-dependent or class-independent pathways. Pronase (Pron) activates the SPE-8 class-dependent pathway, whereas no in vitro tools are available to stimulate the SPE-8 class-independent pathway. Thus, whether there is a functional relationship between these two pathways is currently unclear. In this study, we found that proteinase K (ProK) can activate the SPE-8 class-independent pathway. In vitro spermiogenesis assays using Pron and ProK suggested that SPE-8 class proteins act in the hermaphrodite- and male-dependent spermiogenesis pathways and that some spermatid proteins presumably working downstream of spermiogenesis pathways, including MAP kinases, are preferentially involved in the SPE-8 class-dependent pathway. We screened a library of chemicals, and a compound that we named DDI-1 inhibited both Pron- and ProK-induced spermiogenesis. To our surprise, several DDI-1 analogues that are structurally similar to DDI-1 blocked Pron, but not ProK, induced spermiogenesis. Although the mechanism by which DDI-1 blocks spermiogenesis is yet unknown, we have begun to address this issue by selecting two DDI-1-resistant mutants. Collectively, our data support a model in which C. elegans male and hermaphrodite spermiogenesis each has its own distinct, parallel pathway.

Nuclear envelope dynamics during mammalian spermatogenesis: new insights on male fertility

The production of highly specialized spermatozoa from undifferentiated spermatogonia is a strictly organized and programmed process requiring extensive restructuring of the entire cell. One of the most remarkable cellular transformations accompanying the various phases of spermatogenesis is the profound remodelling of the nuclear architecture, in which the nuclear envelope (NE) seems to be crucially involved. In recent years, several proteins from the distinct layers forming the NE (i.e. the inner and outer nuclear membranes as well as the nuclear lamina) have been associated with meiosis and/or spermiogenesis in different mammalian species. Among these are A- and B-type lamins, Dpy-19-like protein 2 (DPY19L2), lamin B receptor (LBR), lamina-associated polypeptide 1 (LAP1), LAP2/emerin/MAN1 (LEM) domain-containing proteins, spermatogenesis-associated 46 (SPATA46) and diverse elements of the linker of nucleoskeleton and cytoskeleton (LINC) complex, namely Sad-1/UNC-84 homology (SUN) and Klarsicht/ANC-1/Syne-1 homology (KASH) domain-containing proteins. Herein, we summarize the current state of the art on the cellular and subcellular distribution of NE proteins expressed during mammalian spermatogenesis, and discuss the latest research developments regarding their testis-specific functions. This review provides a comprehensive and innovative overview of the NE network as a regulatory platform and as an essential determinant of efficient meiotic chromosome recombination as well as spermiogenesis-associated nuclear remodelling and differentiation in mammalian male germline cells. Thus, this review provides important novel insights on the biological relevance of NE proteins for male fertility.

Genetic Instability and Chromatin Remodeling in Spermatids

The near complete replacement of somatic chromatin in spermatids is, perhaps, the most striking nuclear event known to the eukaryotic domain. The process is far from being fully understood, but research has nevertheless unraveled its complexity as an expression of histone variants and post-translational modifications that must be finely orchestrated to promote the DNA topological change and compaction provided by the deposition of protamines. That this major transition may not be genetically inert came from early observations that transient DNA strand breaks were detected in situ at chromatin remodeling steps. The potential for genetic instability was later emphasized by our demonstration that a significant number of DNA double-strand breaks (DSBs) are formed and then repaired in the haploid context of spermatids. The detection of DNA breaks by 3'OH end labeling in the whole population of spermatids suggests that a reversible enzymatic process is involved, which differs from canonical apoptosis. We have set the stage for a better characterization of the genetic impact of this transition by showing that post-meiotic DNA fragmentation is conserved from human to yeast, and by providing tools for the initial mapping of the genome-wide DSB distribution in the mouse model. Hence, the molecular mechanism of post-meiotic DSB formation and repair in spermatids may prove to be a significant component of the well-known male mutation bias. Based on our recent observations and a survey of the literature, we propose that the chromatin remodeling in spermatids offers a proper context for the induction of de novo polymorphism and structural variations that can be transmitted to the next generation.

Vitamin B12 Prevents Cimetidine-Induced Androgenic Failure and Damage to Sperm Quality in Rats

Cimetidine, used as an anti-ulcer and adjuvant treatment in cancer therapy, causes disorders in the male reproductive tract, including steroidogenesis. However, its effect on sperm quality and male fertility has been poorly addressed. Since vitamin B₁₂ has demonstrated to recover spermatogonia number and sperm concentration in cimetidine-treated rats, we evaluated the impact of cimetidine on sperm quality and fertility potential and whether vitamin B₁₂ is able to prevent the harmful effect of this drug on steroidogenesis and sperm parameters. Adult male rats were treated for 52 consecutive days as follows: cimetidine group (100 mg/kg of cimetidine), cimetidine/vitamin B₁₂ group (100 mg/kg of cimetidine + 3 μg vitamin B₁₂), vitamin B₁₂ group (3 μg vitamin B₁₂) and control group (saline). Serum testosterone levels and immunofluorescence associated to western blot for detection of 17β-HSD6 were performed. Sperm morphology and motility, mitochondrial activity, acrosome integrity, DNA integrity by Comet assay, lipid peroxidation as well as fertility potential were analyzed in all groups. Apoptotic spermatids were also evaluated by caspase-3 immunohistochemistry. In the cimetidine-treated animals, reduced serum testosterone levels, weak 17β-HSD6 levels and impaired spermiogenesis were observed. Low sperm motility and mitochondrial activity were associated with high percentage of sperm tail abnormalities, and the percentage of spermatozoa with damaged acrosome and DNA fragmentation increased. MDA levels were normal in all groups, indicating that the cimetidine-induced changes are associated to androgenic failure. In conclusion, despite the fertility potential of rats was unaffected by the treatment, the sperm quality was significantly impaired. Therefore, considering a possible sperm-mediated transgenerational inheritance, the long term offspring health needs to be investigated. The administration of vitamin B₁₂ to male rats prevents the androgenic failure and counteracts the damage inflicted by cimetidine upon sperm quality, indicating that this vitamin may be used as a therapeutic agent to maintain the androgenic status and the sperm quality in patients exposed to androgen disrupters.

Delayed sexual maturity in males of Vespa velutina

Vespa velutina var nigrithorax (Lepelletier, 1835) is an invasive predator of bees accidentally introduced in France in 2004, and it is having a serious impact on apiculture and ecosystems. Studying the reproduction of an invasive species is key to assess its population dynamic. This study explores the sexual maturation of V. velutina males and the evolution of their fertility. The main studied parameters were physiologic (spermiogenesis, spermatogenesis) and anatomic (testes size and structure, head width). Two populations of males were described based on their emergence period: early males in early summer or classic males in autumn. Each testis has an average of 108 testicular follicles. Spermatogenesis is synchronous, with only 1 sperm production wave, and completed, on average, at 10.3 d after emergence with the degeneration of the testes. The sperm counts in seminal vesicles of mature males are 3 × 10⁶ in October/November and 0.8 × 10⁶ in June. In comparison, females store 0.1 × 10⁶ sperm in their spermathecae. The early males emerged from colonies made by fertilized queens. The reproductive potential of these early males seemed limited, and their function in the colony is discussed. The sperm stock evolution in autumn males suggests the occurrence of a reproductive pattern of male competition for the access to females and a single copulation per male. The synchronicity of male and foundress emergences and sexual maturation is of primary importance for the mating success and the future colony development.

The developmental origin and compartmentalization of glutathione-s-transferase omega 2 isoforms in the perinuclear theca of eutherian spermatozoa

The perinuclear theca (PT) is a condensed, nonionic detergent resistant cytosolic protein layer encapsulating the sperm head nucleus. It can be divided into two regions: the subacrosomal layer, whose proteins are involved in acrosomal assembly during spermiogenesis, and the postacrosomal sheath (PAS), whose proteins are implicated in sperm–oocyte interactions during fertilization. In continuation of our proteomic analysis of the PT, we have isolated two prominent PT-derived proteins of 28 and 31 kDa from demembranated bovine sperm head fractions. These proteins were identified by mass spectrometry as isoforms of glutathione-s-transferase omega 2 (GSTO2). Immunoblots probed with anti-GSTO2 antibodies confirmed the presence of the GSTO2 isoforms in these fractions while fluorescent immunocytochemistry localized the isoforms to the PAS region of the bull, boar, and murid PT. In addition to the PAS labeling of GSTO2, the performatorium of murid spermatozoa was also labeled. Immunohistochemistry of rat testes revealed that GSTO2 was expressed in the third phase of spermatogenesis (i.e., spermiogenesis) and assembled in the PAS and perforatorial regions of late elongating spermatids. Fluorescent immunocytochemistry performed on murine testis cells co-localized GSTO2 and tubulin on the transient microtubular-manchette of elongating spermatids. These findings imply that GSTO2 is transported and deposited in the PAS region by the manchette, conforming to the pattern of assembly found with other PAS proteins. The late assembly of GSTO2 and its localization in the PAS suggests a role in regulating the oxidative and reductive state of covalently linked spermatid/sperm proteins, especially during the disassembly of the sperm accessory structures after fertilization.

IFT25, an intraflagellar transporter protein dispensable for ciliogenesis in somatic cells, is essential for sperm flagella formation

Intraflagellar transport (IFT) is a conserved mechanism essential for the assembly and maintenance of most eukaryotic cilia and flagella. However, IFT25, a component of the IFT complex, is not required for the formation of cilia in somatic tissues. In mice, the gene is highly expressed in the testis, and its expression is upregulated during the final phase when sperm flagella are formed. To investigate the role of IFT25 in sperm flagella formation, the gene was specifically disrupted in male germ cells. All homozygous knockout mice survived to adulthood and did not show any gross abnormalities. However, all homozygous knockout males were completely infertile. Sperm numbers were reduced and these sperm were completely immotile. Multiple morphological abnormalities were observed in sperm, including round heads, short and bent tails, with some tails showing branched flagella and others with frequent abnormal thicknesses, as well as swollen tips of the tail. Transmission electron microscopy revealed that flagellar accessory structures, including the fibrous sheath and outer dense fibers, were disorganized, and most sperm had also lost the "9+2" microtubule structure. In the testis, IFT25 forms a complex with other IFT proteins. In Ift25 knockout testes, IFT27, an IFT25 binding partner, was missing, and IFT20 and IFT81 levels were also reduced. Our findings suggest that IFT25, although not necessary for the formation of cilia in somatic cells, is indispensable for sperm flagellum formation and male fertility in mice.

The histone methyltransferase SETD2 is required for expression of acrosin-binding protein 1 and protamines and essential for spermiogenesis in mice

Spermatogenesis is precisely controlled by complex gene expression programs and involves epigenetic reprogramming, including histone modification and DNA methylation. SET domain-containing 2 (SETD2) is the predominant histone methyltransferase catalyzing the trimethylation of histone H3 lysine 36 (H3K36me3) and plays key roles in embryonic stem cell differentiation and somatic cell development. However, its role in male germ cell development remains elusive. Here, we demonstrate an essential role of Setd2 for spermiogenesis, the final stage of spermatogenesis. Using RNA-seq, we found that, in postnatal mouse testes, Setd2 mRNA levels dramatically increase in 14-day-old mice. Using a germ cell-specific Setd2 knockout mouse model, we also found that targeted Setd2 knockout in germ cells causes aberrant spermiogenesis with acrosomal malformation before step 8 of the round-spermatid stage, resulting in complete infertility. Furthermore, we noted that the Setd2 deficiency results in complete loss of H3K36me3 and significantly decreases expression of thousands of genes, including those encoding acrosin-binding protein 1 (Acrbp1) and protamines, required for spermatogenesis. Our findings thus reveal a previously unappreciated role of the SETD2-dependent H3K36me3 modification in spermiogenesis and provide clues to the molecular mechanisms in epigenetic disorders underlying male infertility.

KIFC1 is essential for acrosome formation and nuclear shaping during spermiogenesis in the lobster Procambarus clarkii

In order to study the function of kinesin-14 motor protein KIFC1 during spermatogenesis of Procambarus clarkii, the full length of kifc1 was cloned from testes cDNA using Rapid-Amplification of cDNA Ends (RACE). The deduced KIFC1 protein sequence showed the highest similarity between Procambarus clarkii and Eriocheir senensis (similarity rate as 64%). According to the results of in situ hybridization (ISH), the kifc1 mRNA was gathered in the acrosome location above nucleus in the mid- and late-stage spermatids. Immunofluorescence results were partly consistent with the ISH in middle spermatids, while in the late spermatids the KIFC1 was distributed around the nucleus which had large deformation and formed four to six nuclear arms. In the mature sperm, KIFC1 and microtubules were distributed around the sperm, playing a role in maintaining the sperm morphology and normal function. Overexpression of P. clarkii kifc1 in GC1 cells for 24 hours resulted in disorganization of microtubules which changed the cell morphology from circular and spherical into fusiform. In addition, the overexpression also resulted in triple centrosomes during mitosis which eventually led to cell apoptosis. RNAi experiments showed that decreased KIFC1 protein levels resulted in total inhibition of spermatogenesis, with only mature sperm found in the RNAi-testis, implying an indispensable role of KIFC1 during P. clarkii spermiogenesis.

Ultrastructural description of the spermatogenesis and spermatozoa in Phaenocora unipunctata (Platyhelminthes, Neotyphloplanida)

Ultrastructural studies of spermiogenesis and sperm morphology have found many characters that are likely to provide clues to the phylogeny of the Platyhelminthes. However, the lack of information on many free-living groups has been a limiting factor. There is a single description of the spermatogenesis and spermatozoa in a Phaenocora species, namely P. anomalocoela, therefore a similar analysis was made in Phaenocora unipunctata to compare the intrageneric variation of sperm ultrastructure and spermatogenesis in the Neotyphloplanida. The comparison of the two Phaenocora species shows that several characters have the potential to be relevant to hypothesize phylogenetic relationships at different taxonomic levels. The presence of superficially incorporated axonemes outside the ring of cortical microtubules in the mature sperm cell, resulting from the fusion of the axonemes with the median cytoplasmic process during spermiogenesis, as well as the presence of a constant number of microtubules in the different regions of the spermatozoon, seem to constitute apomorphies of the genus Phaenocora. Furthermore, the presence of an axonemal spur, the compression of cortical microtubules by the rotation of the basal bodies during spermiogenesis, and the presence of a connection between the nucleus and the plasma membrane in the mature spermatozoon, support previous proposals that these characters are apomorphies of Dalytyphloplanida. The comparison of spermatogenesis and spermatozoa of P. unipunctata and P. anomalocoela demonstrates that studying intrageneric variation can give valuable insights into the significance of many characters proposed for phylogenetic studies of the Rhabdocoela.

The Drosophila chromosomal protein Mst77F is processed to generate an essential component of mature sperm chromatin

In most animals, the bulk of sperm DNA is packaged with sperm nuclear basic proteins (SNBPs), a diverse group of highly basic chromosomal proteins notably comprising mammalian protamines. The replacement of histones with SNBPs during spermiogenesis allows sperm DNA to reach an extreme level of compaction, but little is known about how SNBPs actually function in vivo. Mst77F is a Drosophila SNBP with unique DNA condensation properties in vitro, but its role during spermiogenesis remains unclear. Here, we show that Mst77F is required for the compaction of sperm DNA and the production of mature sperm, through its cooperation with protamine-like proteins Mst35Ba/b. We demonstrate that Mst77F is incorporated in spermatid chromatin as a precursor protein, which is subsequently processed through the proteolysis of its N-terminus. The cleavage of Mst77F is very similar to the processing of protamine P2 during human spermiogenesis and notably leaves the cysteine residues in the mature protein intact, suggesting that they participate in the formation of disulfide cross-links. Despite the rapid evolution of SNBPs, sperm chromatin condensation thus involves remarkably convergent mechanisms in distantly related animals.

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.

Aging deteriorates quality of sperm produced by male mice with partial Yq deletion

The aim of the study was to assess the cumulative effects of aging and Y-chromosome long arm deletion on sperm quality parameters. Motility, mitochondrial activity, and head morphology were evaluated for sperm of 3- and 12-month-old males from B10.BR-Y^del and B10.BR congenic mouse strains. The study revealed that quality and fertilizing potential of sperm produced by younger and older B10.BR males persist on similar levels, but worsen significantly with age of B10.BR-Y^del males. The findings imply that partial Yq deletions might be more harmful for spermiogenesis in advancing age and may be applicable to other species including humans.

ABBREVIATIONS

AZF: azoospermia factor; MSYq: male-specific region of the Y-chromosome long arm.

EPC1/TIP60-Mediated Histone Acetylation Facilitates Spermiogenesis in Mice

Global histone hyperacetylation is suggested to play a critical role for replacement of histones by transition proteins and protamines to compact the genome during spermiogenesis. However, the underlying mechanisms for hyperacetylation-mediated histone replacement remains poorly understood. Here, we report that EPC1 and TIP60, two critical components of the mammalian nucleosome acetyltransferase of H4 (NuA4) complexes, are coexpressed in male germ cells. Strikingly, genetic ablation of either Epc1 or Tip60 disrupts hyperacetylation and impairs histone replacement, in turn causing aberrant spermatid development. Taking these observations together, we reveal an essential role of the NuA4 complexes for histone hyperacetylation and subsequent compaction of the spermatid genome.

BTBD18 Regulates a Subset of piRNA-Generating Loci through Transcription Elongation in Mice

PIWI-interacting RNAs (piRNAs) are small non-coding RNAs essential for animal germ cell development. Despite intense investigation of post-transcriptional processing, chromatin regulators for piRNA biogenesis in mammals remain largely unexplored. Here we document that BTBD18 is a pachytene nuclear protein in mouse testes that occupies a subset of pachytene piRNA-producing loci. Ablation of Btbd18 in mice disrupts piRNA biogenesis, prevents spermiogenesis, and results in male sterility. Transcriptome profiling, chromatin accessibility, and RNA polymerase II occupancy demonstrate that BTBD18 facilitates expression of pachytene piRNA precursors by promoting transcription elongation. Thus, our study identifies BTBD18 as a specific controller for transcription activation through RNA polymerase II elongation at a subset of genomic piRNA loci.

In vivo autophagy and biogenesis of autophagosomes within male haploid cells during spermiogenesis

Autophagy is a unique catabolic pathway that is linked to several physiological processes. However, its role in the process of spermiogenesis is largely unknown. The aim of the current study was to determine the in vivo role of autophagy and the origin of autophagosome membrane biogenesis within male haploid cells. Our immunohistochemistry results demonstrated that LC3 and ATG7 localization were increased dramatically in round to elongated spermatids (haploid cells) towards the lumen of seminiferous tubules, however, poorly expressed in the early stages of germ cells near the basal membrane. Moreover, transmission electron microscopy revealed that the numbers of lysosomes and autophagosomes increased in the elongated spermatids as spermiogenesis progressed. However, no evidence was found for the presence of autophagosomes in the Sertoli cells, spermatogonia or early primary spermatocytes (diploid cells). Furthermore, TEM showed that many endoplasmic reticula were transformed into a “chrysanthemum flower center,” from which a double-layered isolation membrane appeared to develop into an autophagosome. This study provides novel evidence about the formation of autophagosomes through the chrysanthemum flower center from the endoplasmic reticulum, and suggests that autophagy may have an important role in the removal of extra cytoplasm within male haploid cells during spermiogenesis.