Sex body: A nest of protein mixture

During the pachytene stage in mammalian meiosis, the X and Y chromosomes remain largely unsynapsed outside the pseudoautosomal region, while autosomes are fully synapsed. Then, the sex chromosomes are compartmentalized into a "sex body" in the nucleus and are subjected to meiotic sex chromosome inactivation (MSCI). For decades, the formation and functioning of the sex body and MSCI have been subjects worth exploring. Notably, a series of proteins have been reported to be located on the sex body area and inferred to play an essential role in MSCI; however, the proteins that are actually located in this area and how these proteins promote sex body formation and establish MSCI remain unclear. Collectively, the DNA damage response factors, downstream fanconi anemia proteins, and other canonical repressive histone modifications have been reported to be associated with the sex body. Here, this study reviews the factors located on the sex body area and tries to provide new insights into studying this mysterious domain.

Ectopic expression of meiotic cohesin generates chromosome instability in cancer cell line

This work originated from mining of cancer genome data and proceeded to analyze the effects of ectopic expression of meiotic cohesins in mitotic cells in culture. In the process, apart from conclusively answering the question on mechanisms for RAD21L toxicity and its underrepresentation in tumor transcriptomes, we found an association of meiotic cohesin binding with BORIS/CTCFL sites in the normal testis. We also elucidated the patterns and outcomes of meiotic cohesin binding to chromosomes in model cell lines. Furthermore, we uncovered that RAD21L-based meiotic cohesin possesses a self-contained chromosome restructuring activity able to trigger sustainable but imperfect mitotic arrest leading to chromosomal instability. The discovered epigenomic and genetic mechanisms can be relevant to chromosome instability in cancer.

Many tumors express meiotic genes that could potentially drive somatic chromosome instability. While germline cohesin subunits SMC1B, STAG3, and REC8 are widely expressed in many cancers, messenger RNA and protein for RAD21L subunit are expressed at very low levels. To elucidate the potential of meiotic cohesins to contribute to genome instability, their expression was investigated in human cell lines, predominately in DLD-1. While the induction of the REC8 complex resulted in a mild mitotic phenotype, the expression of the RAD21L complex produced an arrested but viable cell pool, thus providing a source of DNA damage, mitotic chromosome missegregation, sporadic polyteny, and altered gene expression. We also found that genomic binding profiles of ectopically expressed meiotic cohesin complexes were reminiscent of their corresponding specific binding patterns in testis. Furthermore, meiotic cohesins were found to localize to the same sites as BORIS/CTCFL, rather than CTCF sites normally associated with the somatic cohesin complex. These findings highlight the existence of a germline epigenomic memory that is conserved in cells that normally do not express meiotic genes. Our results reveal a mechanism of action by unduly expressed meiotic cohesins that potentially links them to aneuploidy and chromosomal mutations in affected cells.

Novel localizations and interactions of intercellular bridge proteins revealed by proteomic profiling†

Intercellular bridges (ICBs) connecting germ cells are essential for spermatogenesis, and their deletion causes male infertility. However, the functions and component factors of ICBs are still unknown. We previously identified novel ICB-associated proteins by proteomics analysis using ICB enrichment. Here, we performed immunoprecipitation-proteomics analyses using antibodies specific to known ICB proteins MKLP1, RBM44, and ectoplasmic specialization-associated protein KIAA1210 and predicted protein complexes in the ICB cores. KIAA1210, its binding protein topoisomerase2B (TOP2B), and tight junction protein ZO1 were identified as novel ICB proteins. On the other hand, as well as KIAA1210 and TOP2B, MKLP1 and RBM44, but not TEX14, were localized at the XY body of spermatocytes, suggesting that there is a relationship between ICB proteins and meiotic chromosomes. Moreover, small RNAs interacted with an ICB protein complex that included KIAA1210, RBM44, and MKLP1. These results indicate dynamic movements of ICB proteins and suggest that ICB proteins could be involved not only in the communication between germ cells but also in their epigenetic regulation. Our results provide a novel perspective on the function of ICBs and could be helpful in revealing the biological function of the ICB.

Effects of body temperature on the expression and localization of meiosis-related proteins STRA8 and SCP3 in boar testes

Body temperature could lead to interruption of spermatogenesis, but the molecular mechanism was still unclear. Cryptorchidism was defined as the failure of testes to enter the scrotum, which exposed the testes to body temperature. Meiosis was a unique feature of germ cell development. Whether cryptorchidism damage the initiation of meiosis in boars had not been reported. The aim of this study was to determine whether spermatogonia in the cryptorchid testes entered into meiosis by detecting meiosis-related markers stimulated by retinoic acid gene 8 (STRA8) and synaptonemal complex protein 3 (SCP3). Three boars with spontaneous unilateral abdominal cryptorchidism were used. The testis located in the abdomen was cryptorchidism group, the scrotal testis of the same animal was used as control. HE results showed that only Sertoli cells, and a few spermatogonia remained in the seminiferous tubules, and no spermatids were seen compared with the control. Immunohistochemistry results showed that in both control and cryptorchidism group, STRA8 was mainly expressed in the nucleus of spermatogonia and spermatocytes. In control group, SCP3 was expressed in the nucleus of spermatocytes. In cryptorchidism group, SCP3 immunopositive cells were also observed. qRT-PCR and Western Blot results showed that the mRNA and protein levels of STRA8 and SCP3 were significantly decreased in cryptorchid boars. The expression of STRA8 and SCP3 in cryptorchidism suggested that spermatogonia could still enter meiosis in cryptorchid boars.

Effect of antiepileptic drug (Topiramate) and cold pressed ginger oil on testicular genes expression, sexual hormones and histopathological alterations in mice

Sexual dysfunction in the epileptic patient is difficult to confirm whether it is ailment or therapy related. Antiepileptic drugs often use in reproductive age, through reproductive progress and maturation. On the other side, cold-pressed oils are rich in bioactive phytochemicals with health-promoting traits. The target of this work was to appraise the sexual dysfunction of antiepileptic Topiramate (TPM) and cold pressed ginger oil (CPGO) as antiepileptic alternative medicine in male mice. Fifty-four adult male albino mice were divided into nine groups (n = 6 mice). One group given saline and used as negative control; another one was given corn oil as vehicle. Six groups administered orally with TPM or CPGO at 100, 200 and 400 mg/kg. Moreover, group of animals co-administrated orally CPGO with TPM (400 mg/kg) to study their interaction. Fatty acid profile and tocols composition of CPGO were determined. in vitro assays were undertaken to evaluate radical scavenging traits of CPGO utilizing sable 1,1-diphenyl-2-picrylhydrazyl (DPPH·) and galvinoxyl radicals. The study investigated antioxidant and oxidative stress markers, sexual hormones levels, mRNA levels of vascular endothelial growth factor (Vegfa), synaptonemal complex protein (Sycp3), Wilms tumor gene (Wt1) as well as histopathological and immunohistochemical examination. Strong radical scavenging potential of CPGO against stable DPPH· and galvinoxyl radicals was recorded. The results revealed that TPM caused a dose-dependent reduction in the antioxidant activities and testosterone content, while, malonaldehyde (MDA) and nitric oxide (NO) as oxidative stress markers were elevated. Vegfa and Sycp3 mRNA expression down-regulated at all Topiramate tested doses, but Wt1 up-regulated at 400 mg/kg. TPM (400 mg/kg) revealed histological alterations associated with strong positive Bax immune reactive spermatogoneal and Leydig cells. Ginger oil elevated the CAT and SOD (antioxidant enzymes), serum testosterone and diminished the oxidative stress, up regulated the expression of Vegfa and Sycp3 and down-regulated the Wt1 expression. Meanwhile, CPGO revealed no histopathological alterations and no Bax immune-reactive cells. CPGO co-administration with TPM (400 mg/kg) attenuated the TPM toxicity. High doses of TPM may exhibit sexual dysfunction but CPGO is safe and has androgenic property. CPGO co-administration could protect the antiepileptic patient from the TPM sexual dysfunction.

Differential cohesin loading marks paired and unpaired regions of platypus sex chromosomes at prophase I

Cohesins are vital for chromosome organisation during meiosis and mitosis. In addition to the important function in sister chromatid cohesion, these complexes play key roles in meiotic recombination, DSB repair, homologous chromosome pairing and segregation. Egg-laying mammals (monotremes) feature an unusually complex sex chromosome system, which raises fundamental questions about organisation and segregation during meiosis. We discovered a dynamic and differential accumulation of cohesins on sex chromosomes during platypus prophase I and specific reorganisation of the sex chromosome complex around a large nucleolar body. Detailed analysis revealed a differential loading of SMC3 on the chromatin and chromosomal axis of XY shared regions compared with the chromatin and chromosomal axes of asynapsed X and Y regions during prophase I. At late prophase I, SMC3 accumulation is lost from both the chromatin and chromosome axes of the asynaptic regions of the chain and resolves into subnuclear compartments. This is the first report detailing unpaired DNA specific SMC3 accumulation during meiosis in any species and allows speculation on roles for cohesin in monotreme sex chromosome organisation and segregation.

Novel compound heterozygous variants in PLK4 identified in a patient with autosomal recessive microcephaly and chorioretinopathy

It has been well documented that variants in genes encoding centrosomal proteins cause primary autosomal recessive microcephaly, although the association between centrosomal defects and the etiology of microcephaly syndromes is not fully understood. Polo-like kinase 4 (PLK4) is one of the centrosomal proteins required for centriole duplication. We here describe a patient with microcephaly and chorioretinopathy that harbors compound heterozygous missense variants, c.[442A>G]; [2336G>A], in the PLK4 gene. One of these variants, c.442A>G (p.(M148V)), resides in the kinase domain, and the other, c.2336G>A (p.(C779Y)), in the polo-box domain. Aberrant spindle formation was observed in a LCL derived from this patient. Overexpression experiments of the variant PLK4 proteins demonstrated that the p.(C779Y) but not the p.(M148V) had lost centriole overduplication ability. The altered mobility pattern of both variant proteins on a western blot further suggested alterations in post-translation modification. Our data lend support to the hypothesis that impaired centriole duplication caused by PLK4 variants may be involved in the etiology of microcephaly disorder.

Germ stem cells are active in postnatal mouse ovary under physiological conditions

STUDY HYPOTHESIS

Are active ovarian germ stem cells present in postnatal mouse ovaries under physiological conditions?

STUDY FINDING

Active ovarian germ stem cells exist and function in adult mouse ovaries under physiological conditions.

WHAT IS KNOWN ALREADY

In vitro studies suggested the existence of germ stem cells in postnatal ovaries of mouse, pig and human. However, in vivo studies provided evidence against the existence of active germ stem cells in postnatal mouse ovaries. Thus, it remains controversial whether such germ stem cells really exist and function in vivo in postnatal mammalian ovaries.

STUDY DESIGN, SAMPLES/MATERIALS, METHODS

Octamer-binding transcription factor 4 (Oct4)-MerCreMer transgenic mice were crossed with R26R-enhanced yellow fluorescent protein (EYFP) mice to establish a tamoxifen-inducible tracing system so that Oct4-expressing potential ovarian germ stem cells in young adult mice (5-6 weeks old) can be labeled with EYFP. The germ cell activities of DNA replication, mitotic division, entry into meiosis and progression to primordial follicle stage were investigated by means of immunofluorescent staining of ovarian tissues collected at different time points post-tamoxifen injection (1 day, 3 days, 2 months and 4 months). Meiosis entry and primordial follicle formation were also measured by EYFP-labeled single-cell RT-PCR. Germ cell proliferation and mitotic division were examined through 5-bromodeoxyuridine triphosphate incorporation assay. At each time point, ovaries from two to three animals were used for each set of experiment.

MAIN RESULTS AND THE ROLE OF CHANCE

By labeling the Oct4-expressing small germ cells and tracing their fates for up to 4 months, we observed persistent meiosis entry and primordial follicle replenishment. Furthermore, we captured the transient processes of mitotic DNA replication as well as mitotic division of the marked germ cells at various time periods after tracing. These lines of evidence unambiguously support the presence of active germ stem cells in postnatal ovaries and their function in replenishing primordial follicle pool under physiological conditions. Moreover, we pointed out that Oct4(+) deleted in azoospermia-like (Dazl)(-) but not Oct4(+)Dazl(+) or Oct4(+) DEAD (Asp-Glu-Ala-Asp) Box Polypeptide 4 (Ddx4)(+) cells contain a population of germ stem cells in mouse ovary.

LIMITATIONS, REASONS FOR CAUTION

This study was conducted in mice. Whether or not the results are applicable to human remain unclear. The future work should aim at identifying the specific ovarian germ stem cell marker and evaluating the significance of these stem cells to normal ovarian function.

WIDER IMPLICATIONS OF THE FINDINGS

Clarifying the existence of active germ stem cells and their functional significance in postnatal mammalian ovaries could provide new insights in understanding the mechanism of ovarian aging and failure.

LARGE SCALE DATA

Not applicable.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by the National Key Basic Research Program of China (grant number 2012CBA01300) and the National Natural Science Foundation of China to P.Z. (31571484). No competing interests are reported.

CRISPR/Cas9 Promotes Functional Study of Testis Specific X-Linked Gene In Vivo

Mammalian spermatogenesis is a highly regulated multistage process of sperm generation. It is hard to uncover the real function of a testis specific gene in vitro since the in vitro model is not yet mature. With the development of the CRISPR/Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR-associated 9) system, we can now rapidly generate knockout mouse models of testis specific genes to study the process of spermatogenesis in vivo. SYCP3-like X-linked 2 (SLX2) is a germ cell specific component, which contains a Cor1 domain and belongs to the XLR (X-linked, lymphocyte regulated) family. Previous studies suggested that SLX2 might play an important role in mouse spermatogenesis based on its subcellular localization and interacting proteins. However, the function of SLX2 in vivo is still elusive. Here, to investigate the functions of SLX2 in spermatogenesis, we disrupted the Slx2 gene by using the CRISPR/Cas9 system. Since Slx2 is a testis specific X-linked gene, we obtained knockout male mice in the first generation and accelerated the study process. Compared with wild-type mice, Slx2 knockout mice have normal testis and epididymis. Histological observation of testes sections showed that Slx2 knockout affected none of the three main stages of spermatogenesis: mitosis, meiosis and spermiogenesis. In addition, we further confirmed that disruption of Slx2 did not affect the number of spermatogonial stem cells, meiosis progression or XY body formation by immunofluorescence analysis. As spermatogenesis was normal in Slx2 knockout mice, these mice were fertile. Taken together, we showed that Slx2 itself is not an essential gene for mouse spermatogenesis and CRISPR/Cas9 technique could speed up the functional study of testis specific X-linked gene in vivo.

The chromatin regulator Brpf1 regulates embryo development and cell proliferation

With hundreds of chromatin regulators identified in mammals, an emerging issue is how they modulate biological and pathological processes. BRPF1 (bromodomain- and PHD finger-containing protein 1) is a unique chromatin regulator possessing two PHD fingers, one bromodomain and a PWWP domain for recognizing multiple histone modifications. In addition, it binds to the acetyltransferases MOZ, MORF, and HBO1 (also known as KAT6A, KAT6B, and KAT7, respectively) to promote complex formation, restrict substrate specificity, and enhance enzymatic activity. We have recently showed that ablation of the mouse Brpf1 gene causes embryonic lethality at E9.5. Here we present systematic analyses of the mutant animals and demonstrate that the ablation leads to vascular defects in the placenta, yolk sac, and embryo proper, as well as abnormal neural tube closure. At the cellular level, Brpf1 loss inhibits proliferation of embryonic fibroblasts and hematopoietic progenitors. Molecularly, the loss reduces transcription of a ribosomal protein L10 (Rpl10)-like gene and the cell cycle inhibitor p27, and increases expression of the cell-cycle inhibitor p16 and a novel protein homologous to Scp3, a synaptonemal complex protein critical for chromosome association and embryo survival. These results uncover a crucial role of Brpf1 in controlling mouse embryo development and regulating cellular and gene expression programs.

Surface-spreading technique of meiotic cells and immunodetection of synaptonemal complex proteins in teleostean fishes

Background

Different moderrn methodologies are presently available to analyze meiotic chromosomes. These methods permit investigation of the behavior of chromosomes in the normal complement and of sex and B chromosomes, two special types of chromosomes that are associated with the A complement and are present in many organisms, including fishes. However, meiotic studies are still scarce in fishes, considering the wide number of species in this group.. Here, we describe a new protocol for the visualization of the synaptonemal complex in spermatocytes and oocytes of fishes and to the sequential use of the technique with other procedures and techniques such as immunodetection of the synaptonemal complex protein with a specific antibody and co-detection of DNA sequences by FISH.

Results

The meiotic surface-spreading protocol used in the present proposal worked well in representative species of four fish orders and was useful in obtaining good results even in small specimens. Fish-specific antibodies and commercial products worked similarly well to detect synaptonemal complex (SC) proteins. The sequential application of fluorescence in situ hybridization using specific probes showed clear signals associated with the SC structures identified by immunostaining.

Conclusion

Here, we provide a useful and applicable immunofluorescent protocol for the visualization of synaptonemal complex proteins in the meiotic cells of fishes in surface-spreading preparations. Furthermore, this technique allows for the sequential application of other cytogenetic procedures.

SLX2 interacting with BLOS2 is differentially expressed during mouse oocyte meiotic maturation

Gametogenesis is a complex biological process of producing cells for sexual reproduction. Xlr super family members containing a conserved COR1 domain play essential roles in gametogenesis. In the present study, we identified that Slx2, a novel member of Xlr super family, is specifically expressed in the meiotic oocytes, which is demonstrated by western blotting and immunohistochemistry studies. In the first meiotic prophase, SLX2 is unevenly distributed in the nuclei of oocytes, during which phase SLX2 is partly co-localized with SYCP3 in synaptonemal complex and γH2AX in the nucleus of oocytes. Interestingly, the localization of SLX2 was found to be switched into the cytoplasm of oocytes after prometaphase I during oocyte maturation. Furthermore, yeast two-hybrid and coimmunoprecipitation studies demonstrated that SLX2 interacts with BLOS2, which is a novel centrosome-associated protein, and co-localized with γ-Tubulin, which is a protein marker of chromosome segregation in meiosis. These results indicated that SLX2 might get involved in chromosomes segregation during meiosis by interaction with BLOS2. In conclusion, SLX2 might be a novel gametogenesis-related protein that could play multiple roles in regulation of meiotic processes including synaptonemal complex assembly and chromosome segregation.

Failure of homologous synapsis and sex-specific reproduction problems

The prophase of meiosis I ensures the correct segregation of chromosomes to each daughter cell. This includes the pairing, synapsis, and recombination of homologous chromosomes. A subset of chromosomal abnormalities, including translocation and inversion, disturbs these processes, resulting in the failure to complete synapsis. This activates the meiotic pachytene checkpoint, and the gametes are fated to undergo cell cycle arrest and subsequent apoptosis. Spermatogenic cells appear to be more vulnerable to the pachytene checkpoint, and male carriers of chromosomal abnormalities are more susceptible to infertility. In contrast, oocytes tend to bypass the checkpoint and instead generate other problems, such as chromosome imbalance that often leads to recurrent pregnancy loss in female carriers. Recent advances in genetic manipulation technologies have increased our knowledge about the pachytene checkpoint and surveillance systems that detect chromosomal synapsis. This review focuses on the consequences of synapsis failure in humans and provides an overview of the mechanisms involved. We also discuss the sexual dimorphism of the involved pathways that leads to the differences in reproductive outcomes between males and females.

Screening of genes involved in chromosome segregation during meiosis I: in vitro gene transfer to mouse fetal oocytes

The events that take place during the prophase of meiosis I are essential for the correct segregation of homologous chromosomes. Defects in these processes likely contribute to infertility or recurrent pregnancy loss in humans. To screen for candidate genes for reproductive failure due to meiotic defects, we have analyzed the gene expression patterns in fetal, neonatal and adult gonads of both male and female mice by microarray and thereby identified 241 genes that are expressed specifically during prophase of meiosis I. Combined with our previous data obtained from developing spermatocytes, a total of 99 genes were identified that are upregulated in early prophase I. We confirmed the meiotic prophase I-specific expression of these genes using qRT-PCR. To further screen this panel for candidate genes that fulfill important roles in homologous pairing, synapsis and recombination, we established a gene transfer system for prophase I oocytes in combination with in vitro organ culture of ovaries, and successfully determined the localization of the selected genes. This gene set can thus serve as a resource for targeted sequence analysis via next-generation sequencing to identify the genes associated with human reproduction failure due to meiotic defects.

[Organization, function and genetic controlling of synaptonemal complex]

The synaptonemal complex (SC) is a super protein lattice that connects paired homologous chromosomes in most meiotic systems. This special organization is related to the meiosis processes such as homologous chromosomes pairing, synapsis, recombination, segregation, etc. Flaws of it would lead the meiocytes to apoptosis, which contributes to sterility. In recent years, the study of this complex has been a hotspot in meiosis research, but little was known about its exact mechanism. This review summarized the organization, function, and genetics of this complex with recent advances. Prospects of its further study were also briefly discussed..

Sex chromosome inactivation in germ cells: emerging roles of DNA damage response pathways

Sex chromosome inactivation in male germ cells is a paradigm of epigenetic programming during sexual reproduction. Recent progress has revealed the underlying mechanisms of sex chromosome inactivation in male meiosis. The trigger of chromosome-wide silencing is activation of the DNA damage response (DDR) pathway, which is centered on the mediator of DNA damage checkpoint 1 (MDC1), a binding partner of phosphorylated histone H2AX (γH2AX). This DDR pathway shares features with the somatic DDR pathway recognizing DNA replication stress in the S phase. Additionally, it is likely to be distinct from the DDR pathway that recognizes meiosis-specific double-strand breaks. This review article extensively discusses the underlying mechanism of sex chromosome inactivation.