Three-color dSTORM Imaging and Analysis of Recombination Foci in Mouse Spread Meiotic Nuclei.

During the first meiotic prophase in mouse, repair of SPO11-induced DNA double-strand breaks (DSBs), facilitating homologous chromosome synapsis, is essential to successfully complete the first meiotic cell division. Recombinases RAD51 and DMC1 play an important role in homology search, but their mechanistic contribution to this process is not fully understood. Super-resolution, single-molecule imaging of RAD51 and DMC1 provides detailed information on recombinase accumulation on DSBs during meiotic prophase. Here, we present a detailed protocol of recombination foci analysis of three-color direct stochastic optical reconstruction microscopy (dSTORM) imaging of SYCP3, RAD51, and DMC1, fluorescently labeled by antibody staining in mouse spermatocytes. This protocol consists of sample preparation, data acquisition, pre-processing, and data analysis. The sample preparation procedure includes an updated version of the nuclear spreading of mouse testicular cells, followed by immunocytochemistry and the preparation steps for dSTORM imaging. Data acquisition consists of three-color dSTORM imaging, which is extensively described. The pre-processing that converts fluorescent signals to localization data also includes channel alignment and image reconstruction, after which regions of interest (ROIs) are identified based on RAD51 and/or DMC1 localization patterns. The data analysis steps then require processing of the fluorescent signal localization within these ROIs into discrete nanofoci, which can be further analyzed. This multistep approach enables the systematic investigation of spatial distributions of proteins associated with individual DSB sites and can be easily adapted for analyses of other foci-forming proteins. All computational scripts and software are freely accessible, making them available to a broad audience. Key features Preparation of spread nuclei, resulting in a flattened preparation with easy antibody-accessible chromatin-associated proteins on dSTORM-compatible coverslips. dSTORM analysis of immunofluorescent repair foci in meiotic prophase nuclei. Detailed descriptions of data acquisition, (pre-)processing, and nanofoci feature analysis applicable to all proteins that assemble in immunodetection as discrete foci. Graphical overview.

Identification of fish spermatogenic cells through high-throughput immunofluorescence against testis with an antibody set.

Image-based identification and quantification of different types of spermatogenic cells is of great importance, not only for reproductive studies but also for genetic breeding. Here, we have developed antibodies against spermatogenesis-related proteins in zebrafish (Danio rerio), including Ddx4, Piwil1, Sycp3, and Pcna, and a high-throughput method for immunofluorescence analysis of zebrafish testicular sections. By immunofluorescence analysis of zebrafish testes, our results demonstrate that the expression of Ddx4 decreases progressively during spermatogenesis, Piwil1 is strongly expressed in type A spermatogonia and moderately expressed in type B spermatogonia, and Sycp3 has distinct expression patterns in different subtypes of spermatocytes. Additionally, we observed polar expression of Sycp3 and Pcna in primary spermatocytes at the leptotene stage. By a triple staining of Ddx4, Sycp3, and Pcna, different types/subtypes of spermatogenic cells were easily characterized. We further demonstrated the practicality of our antibodies in other fish species, including Chinese rare minnow (Gobiocypris rarus), common carp (Cyprinus carpio), blunt snout bream (Megalobrama amblycephala), rice field eel (Monopterus albus) and grass carp (Ctenopharyngodon idella). Finally, we proposed an integrated criterion for identifying different types/subtypes of spermatogenic cells in zebrafish and other fishes using this high-throughput immunofluorescence approach based on these antibodies. Therefore, our study provides a simple, practical, and efficient tool for the study of spermatogenesis in fish species.

A molecular cell biology toolkit for the study of meiosis in the silkworm Bombyx mori.

Meiosis is usually described as 4 essential and sequential processes: (1) homolog pairing; (2) synapsis, mediated by the synaptonemal complex; (3) crossing over; and (4) segregation. In this canonical model, the maturation of crossovers into chiasmata plays a vital role in holding homologs together and ensuring their segregation at the first meiotic division. However, Lepidoptera (moths and butterflies) undergo 3 distinct meiotic processes, only one of which is canonical. Lepidoptera males utilize 2 meiotic processes: canonical meiosis that produces nucleated fertile sperm, and a noncanonical meiosis that produces anucleated nonfertile sperm which are nonetheless essential for reproduction. Lepidoptera females, which carry heteromorphic sex chromosomes, undergo a completely achiasmate (lacking crossovers) meiosis, thereby requiring an alternative mechanism to ensure proper homolog segregation. Here, we report that the development of a molecular cell biology toolkit designed to properly analyze features of meiosis, including the synaptonemal complex structure and function, in the silkworm Bombyx mori. In addition to standard homology searches to identify Bombyx orthologs of known synaptonemal complex encoding genes, we developed an ortholog discovery app (Shinyapp) to identify Bombyx orthologs of proteins involved in several meiotic processes. We used this information to clone genes expressed in the testes and then created antibodies against their protein products. We used the antibodies to confirm the localization of these proteins in normal male spermatocytes, as well as using in vitro assays to confirm orthologous interactions. The development of this toolkit will facilitate further study of the unique meiotic processes that characterize meiosis in Lepidoptera.

Genic and chromosomal components of Prdm9-driven hybrid male sterility in mice (Mus musculus).

Hybrid sterility contributes to speciation by preventing gene flow between related taxa. Prdm9, the first and only hybrid male sterility gene known in vertebrates, predetermines the sites of recombination between homologous chromosomes and their synapsis in early meiotic prophase. The asymmetric binding of PRDM9 to heterosubspecific homologs of Mus musculus musculus × Mus musculus domesticus F1 hybrids and increase of PRDM9-independent DNA double-strand break hotspots results indificult- to- repair double-strand breaks, incomplete synapsis of homologous chromosomes, and meiotic arrest at the first meiotic prophase. Here, we show that Prdm9 behaves as a major hybrid male sterility gene in mice outside the Mus musculus musculus × Mus musculus domesticus F1 hybrids, in the genomes composed of Mus musculus castaneus and Mus musculus musculus chromosomes segregating on the Mus musculus domesticus background. The Prdm9cst/dom2 (castaneus/domesticus) allelic combination secures meiotic synapsis, testes weight, and sperm count within physiological limits, while the Prdm9msc1/dom2 (musculus/domesticus) males show a range of fertility impairment. Out of 5 quantitative trait loci contributing to the Prdm9msc1/dom2-related infertility, 4 control either meiotic synapsis or fertility phenotypes and 1 controls both, synapsis, and fertility. Whole-genome genotyping of individual chromosomes showed preferential involvement of nonrecombinant musculus chromosomes in asynapsis in accordance with the chromosomal character of hybrid male sterility. Moreover, we show that the overall asynapsis rate can be estimated solely from the genotype of individual males by scoring the effect of nonrecombinant musculus chromosomes. Prdm9-controlled hybrid male sterility represents an example of genetic architecture of hybrid male sterility consisting of genic and chromosomal components.

FBXW24 controls female meiotic prophase progression by regulating SYCP3 ubiquitination.

BACKGROUND: An impeccable female meiotic prophase is critical for producing a high-quality oocyte and, ultimately, a healthy newborn. SYCP3 is a key component of the synaptonemal complex regulating meiotic homologous recombination. However, what regulates SYCP3 stability is unknown. METHODS: Fertility assays, follicle counting, meiotic prophase stage (leptotene, zygotene, pachytene and diplotene) analysis and live imaging were employed to examine how FBXW24 knockout (KO) affect female fertility, follicle reserve, oocyte quality, meiotic prophase progression of female germ cells, and meiosis of oocytes. Western blot and immunostaining were used to examined the levels & signals (intensity, foci) of SYCP3 and multiple key DSB indicators & repair proteins (γH2AX, RPA2, p-CHK2, RAD51, MLH1, HORMAD1, TRIP13) after FBXW24 KO. Co-IP and immuno-EM were used to examined the interaction between FBXW24 and SYCP3; Mass spec was used to characterize the ubiquitination sites in SYCP3; In vivo & in vitro ubiquitination assays were utilized to determine the key sites in SYCP3 & FBXW24 for ubiquitination. RESULTS: Fbxw24-knockout (KO) female mice were infertile due to massive oocyte death upon meiosis entry. Fbxw24-KO oocytes were defective due to elevated DNA double-strand breaks (DSBs) and inseparable homologous chromosomes. Fbxw24-KO germ cells showed increased SYCP3 levels, delayed prophase progression, increased DSBs, and decreased crossover foci. Next, we found that FBXW24 directly binds and ubiquitinates SYCP3 to regulate its stability. In addition, several key residues important for SYCP3 ubiquitination and FBXW24 ubiquitinating activity were characterized. CONCLUSIONS: We proposed that FBXW24 regulates the timely degradation of SYCP3 to ensure normal crossover and DSB repair during pachytene. FBXW24-KO delayed SYCP3 degradation and DSB repair from pachytene until metaphase II (MII), ultimately causing failure in oocyte maturation, oocyte death, and infertility.

Zebrafish Establish Female Germ Cell Identity by Advancing Cell Proliferation and Meiosis.

Zebrafish is a popular research model; but its mechanism of sex determination is unclear and the sex of juvenile fish cannot be distinguished. To obtain fish with defined sex, we crossed domesticated zebrafish with the Nadia strain that has a female-dominant W segment. These fish were placed on a ziwi:GFP background to facilitate sorting of fluorescent germ cells for transcriptomic analysis. We analyzed the transcriptomes of germ cells at 10-14 days postfertilization (dpf), when sex dimorphic changes started to appear. Gene ontology showed that genes upregulated in the 10-dpf presumptive females are involved in cell cycles. This correlates with our detection of increased germ cell numbers and proliferation. We also detected upregulation of meiotic genes in the presumptive females at 14 dpf. Disruption of a meiotic gene, sycp3, resulted in sex reversal to infertile males. The germ cells of sycp3 mutants could not reach diplotene and underwent apoptosis. Preventing apoptosis by disrupting tp53 restored female characteristics in sycp3 mutants, demonstrating that adequate germ cells are required for female development. Thus, our transcriptome and gene mutation demonstrate that initial germ cell proliferation followed by meiosis is the hallmark of female differentiation in zebrafish.

The TERB1 MYB domain suppresses telomere erosion in meiotic prophase I.

The meiosis-specific telomere-binding protein TERB1 anchors telomeres to the nuclear envelope and drives chromosome movements for the pairing of homologous chromosomes. TERB1 has an MYB-like DNA-binding (MYB) domain, which is a hallmark of telomeric DNA-binding proteins. Here, we demonstrate that the TERB1 MYB domain has lost its canonical DNA-binding activity. The analysis of Terb1 point mutant mice expressing TERB1 lacking its MYB domain showed that the MYB domain is dispensable for telomere localization of TERB1 and the downstream TERB2-MAJIN complex, the promotion of homologous pairing, and even fertility. Instead, the TERB1 MYB domain regulates the enrichment of cohesin and promotes the remodeling of axial elements in the early-to-late pachytene transition, which suppresses telomere erosion. Considering its conservation across metazoan phyla, the TERB1 MYB domain is likely to be important for the maintenance of telomeric DNA and thus for genomic integrity by suppressing meiotic telomere erosion over long evolutionary timescales.

Germline-Restricted Chromosome (GRC) in Female and Male Meiosis of the Great Tit (Parus major, Linnaeus, 1758).

All songbirds studied so far have a germline-restricted chromosome (GRC), which is present in the germ cells and absent in the somatic cells. It shows a wide variation in size, morphology, and genetic content between the songbird species. In this paper, we analyzed GRC behavior in female and male meiosis of the great tit, using immunolocalization of meiotic proteins and FISH with GRC-derived DNA probes. We found that, despite dozens of million years of independent evolution, the great tit GRC displays a striking similarity with the GRCs of two species of martins and two species of estrildid finches examined earlier. It was usually present in two copies in females forming recombining bivalent and in one copy in males forming a condensed heterochromatic body with dotted-like axial elements of the synaptonemal complex. We observed mosaicism for the GRC copy number in the female and male great tit. This indicates that one of the GRC copies might be passively lost during premeiotic germ cell divisions. After the meiotic prophase, the GRC was ejected from most male germ cells. The reverse and interspecies FISH with GRC-specific microdissected DNA probes indicates that GRCs of the great tit, pale martin, and zebra finch differ substantially in their genetic content despite similarities in the meiotic behavior.

Highly Conservative Pattern of Sex Chromosome Synapsis and Recombination in Neognathae Birds.

We analyzed the synapsis and recombination between Z and W chromosomes in the oocytes of nine neognath species: domestic chicken Gallus gallus domesticus, grey goose Anser anser, black tern Chlidonias niger, common tern Sterna hirundo, pale martin Riparia diluta, barn swallow Hirundo rustica, European pied flycatcher Ficedula hypoleuca, great tit Parus major and white wagtail Motacilla alba using immunolocalization of SYCP3, the main protein of the lateral elements of the synaptonemal complex, and MLH1, the mismatch repair protein marking mature recombination nodules. In all species examined, homologous synapsis occurs in a short region of variable size at the ends of Z and W chromosomes, where a single recombination nodule is located. The remaining parts of the sex chromosomes undergo synaptic adjustment and synapse non-homologously. In 25% of ZW bivalents of white wagtail, synapsis and recombination also occur at the secondary pairing region, which probably resulted from autosome-sex chromosome translocation. Using FISH with a paint probe specific to the germline-restricted chromosome (GRC) of the pale martin on the oocytes of the pale martin, barn swallow and great tit, we showed that both maternally inherited songbird chromosomes (GRC and W) share common sequences.

Heterochiasmy and Sexual Dimorphism: The Case of the Barn Swallow (Hirundo rustica, Hirundinidae, Aves).

Heterochiasmy, a sex-based difference in recombination rate, has been detected in many species of animals and plants. Several hypotheses about evolutionary causes of heterochiasmy were proposed. However, there is a shortage of empirical data. In this paper, we compared recombination related traits in females and males of the barn swallow Hirundo rustica (Linnaeus, 1758), the species under strong sexual selection, with those in the pale martin Riparia diluta (Sharpe and Wyatt, 1893), a related and ecologically similar species with the same karyotype (2N = 78), but without obvious sexual dimorphism. Recombination traits were examined in pachytene chromosome spreads prepared from spermatocytes and oocytes. Synaptonemal complexes and mature recombination nodules were visualized with antibodies to SYCP3 and MLH1 proteins, correspondingly. Recombination rate was significantly higher (p = 0.0001) in barn swallow females (55.6 ± 6.3 recombination nodules per autosomal genome), caused by the higher number of nodules at the macrochromosomes, than in males (49.0 ± 4.5). They also showed more even distribution of recombination nodules along the macrochromosomes. At the same time, in the pale martin, sexual differences in recombination rate and distributions were rather small. We speculate that an elevated recombination rate in the female barn swallows might have evolved as a compensatory reaction to runaway sexual selection in males.

Retinoic acid and androgen influence germ cells development and meiotic initiation in juvenile orange-spotted grouper, Epinephelus coioides.

Meiosis is essential for germ cells development for all sexually reproducing species. Retinoic acid (RA) is the key factor controlling the sex-specific timing of meiotic initiation in mammals, birds and tetrapods. Here, we investigated the effects of RA on meiotic initiation and sex determination in protogynous hermaphrodite orange-spotted grouper (Epinephelus coioides). Expression profile investigations of meiotic marker genes during gonadal development indicated that germ cells undergone meiosis approximately at 180 days after hatching in the orange-spotted grouper. RA synthase inhibitor treatments on juvenile orange-spotted groupers resulted in impeded germ cells development and delayed meiotic initiation with simultaneous down-regulation of vasa, dazl, sycp3 and rec8, which was rescued by exogenous RA administration. Additionally, exogenous androgen treated fish showed a delayed meiotic initiation consistent with decreased sycp3 and rec8 expression and were directed to a spermiogenesis fate. Our results imply that meiotic initiation in the orange-spotted grouper is strongly influenced by RA and androgen, and the regulation of meiotic initiation may involve in the spermatogenesis induced by exogenous androgen.

Molecular Cloning and Characterization of SYCP3 and TSEG2 Genes in the Testicles of Sexually Mature and Immature Yak.

Testis-specific genes play an essential part in the centromere union during meiosis in male germ cells, spermatogenesis, and in fertility. Previously, there was no research report available on the expression pattern of SYCP3 and TSEG2 genes in different ages of yaks. Therefore, the current research compared the expression profiling of SYCP3 and TSEG2 genes in testes of yaks. The expression pattern of SYCP3 and TSEG2 mRNA was investigated using qPCR, semi-quantitative PCR, western blot, immunohistochemistry, and molecular bioinformatics. Our findings displayed that SYCP3 and TSEG2 genes were prominently expressed in the testicles of yaks as compared to other organs. On the other hand, the protein encoded by yak SYCP3 contains Cor1/Xlr/Xmr conserved regions, while the protein encoded by yak TSEG2 contains synaptonemal complex central element protein 3. Additionally, multiple alignments sequences indicated that proteins encoded by Datong yak SYCP3 and TSEG2 were highly conserved among mammals. Moreover, western blot analysis specified that the molecular mass of SYCP3 protein was 34-kDa and TSEG2 protein 90-kDa in the yak. Furthermore, the results of immunohistochemistry also revealed the prominent expression of these proteins in the testis of mature yaks, which indicated that SYCP3 and TSEG2 might be essential for spermatogenesis, induction of central element assembly, and homologous recombination.

Molecular architecture of the SYCP3 fibre and its interaction with DNA.

The synaptonemal complex (SC) keeps homologous chromosomes in close alignment during meiotic recombination. A hallmark of the SC is the presence of its constituent protein SYCP3 on the chromosome axis. During SC assembly, SYCP3 is deposited on both axes of the homologue pair, forming axial elements that fuse into the lateral element (LE) in the tripartite structure of the mature SC. We have used cryo-electron tomography and atomic force microscopy to study the mechanism of assembly and DNA binding of the SYCP3 fibre. We find that the three-dimensional architecture of the fibre is built on a highly irregular arrangement of SYCP3 molecules displaying very limited local geometry. Interaction between SYCP3 molecules is driven by the intrinsically disordered tails of the protein, with no contact between the helical cores, resulting in a flexible fibre assembly. We demonstrate that the SYCP3 fibre can engage in extensive interactions with DNA, indicative of an efficient mechanism for incorporation of DNA within the fibre. Our findings suggest that SYCP3 deposition on the chromosome axis might take place by polymerization into a fibre that is fastened to the chromosome surface via DNA binding.

Histochemical Study of the Emergence of Apoptosis and Altered SYCP3 Protein Distribution During the First Spermatogenic Wave in Wistar Rats.

Apoptosis is a type of cell death responsible for maintaining tissue homeostasis that can occur in male gonads. The morphological and biochemical characteristics of apoptosis include cellular contraction, caspase activation, and DNA fragmentation. Dynamic processes of cell renewal and differentiation occur inside the seminiferous tubules, which are regulated by mitosis and meiosis, respectively. During meiosis, recombination is caused by assembly of the synaptonemal complex, which involves the participation of constitutive proteins, such as synaptonemal complex protein-3 (SYCP3). The present study evaluated germinal cell death in immature male rats and the distribution of the SYCP3 protein. Our results indicate that as germinal cells progress to the second meiotic stage, significant numbers of them are eliminated by apoptosis. We determined that the SYCP3 protein is not always incorporated into the structure of the synaptonemal complex but rather forms a nuclear cumulus near the inner nuclear membrane, causing many of these cells to undergo apoptosis. We propose that both the excess of the SYCP3 protein and its accumulation during the first meiotic division could contribute to the cell death of primary spermatocytes during the first spermatogenic wave in prepubertal Wistar rats. Anat Rec, 302:2082-2092, 2019. © 2019 American Association for Anatomy.

Sohlh1 is required for synaptonemal complex formation by transcriptionally regulating meiotic genes during spermatogenesis in mice.

Gonad-specific transcription factor spermatogenesis- and oogenesis-specific helix-loop-helix transcription factor 1 (SOHLH1) plays a key role in the transcriptional regulation of the expression of differentiating spermatogonial genes. However, its role in spermatocytes (meiotic male germ cells) remains largely unknown. In this study, Sohlh1 knockout (KO) male mice displayed meiotic defects at the zygotene stage during spermatogenesis. Microarray analyses identified 66 upregulated genes and 139 downregulated genes in Sohlh1 KO testes compared with those in wild-type testes at postnatal Day 7.5. Among many of the downregulated genes, Sycp1 and Sycp3, which encode synaptonemal complex proteins 1 and 3 (SYCP1 and SYCP3), respectively, were significantly reduced in Sohlh1 knockout mice. Transmission electron microscopy revealed no formation of the synaptonemal complex in Sohlh1 KO spermatocytes. Luciferase reporter and chromatin-immunoprecipitation assays demonstrated that SOHLH1 enhanced the expression of the Sycp1 and Sycp3 genes by binding the -1276, -708, and -94 basepairs (bp) E-boxes upstream of the Sycp1 promoter and the -64 and -43 bp E-boxes upstream of the Sycp3 promoter. Our data suggest that SOHLH1 transcriptionally regulates the expression of many target genes critical for the meiotic phase of spermatogenesis.

Cryo-electron tomography of SYCP3 fibers under native conditions.

The synaptonemal complex (SC) forms during the early stages of meiotic prophase I, when it mediates the pairing of homologous chromosomes. Despite the crucial role of the SC in chromosome synapsis and genetic recombination, the molecular details of its function are still unclear. High-resolution information on the structure of SC proteins would be very valuable to elucidate the molecular basis of their function in meiosis. Here we show how cryo-electron tomography and subtomographic averaging can be usefully applied to provide insights into the structure of the helical SYCP3 protein in its filamentous state. The establishment of such method should prove of use for structural studies of other SC proteins, such as SYCP1 and the TEX12-SYCE2 complex, which can form physiologically relevant filamentous assemblies, and ultimately for the structural analysis of the SC.

Chromosome Synapsis and Recombination in Male-Sterile and Female-Fertile Interspecies Hybrids of the Dwarf Hamsters (Phodopus, Cricetidae).

Hybrid sterility is an important step in the speciation process. Hybrids between dwarf hamsters Phodopus sungorus and P.campbelli provide a good model for studies in cytological and genetic mechanisms of hybrid sterility. Previous studies in hybrids detected multiple abnormalities of spermatogenesis and a high frequency of dissociation between the X and Y chromosomes at the meiotic prophase. In this study, we found that the autosomes of the hybrid males and females underwent paring and recombination as normally as their parental forms did. The male hybrids showed a significantly higher frequency of asynapsis and recombination failure between the heterochromatic arms of the X and Y chromosomes than the males of the parental species. Female hybrids as well as the females of the parental species demonstrated a high incidence of centromere misalignment at the XX bivalent and partial asynapsis of the ends of its heterochromatic arms. In all three karyotypes, recombination was completely suppressed in the heterochromatic arm of the X chromosome, where the pseudoautosomal region is located. We propose that this recombination pattern speeds up divergence of the X- and Y-linked pseudoautosomal regions between the parental species and results in their incompatibility in the male hybrids.

Live cell analyses of synaptonemal complex dynamics and chromosome movements in cultured mouse testis tubules and embryonic ovaries.

During mammalian meiotic prophase, homologous chromosomes connect through the formation of the synaptonemal complex (SC). SYCP3 is a component of the lateral elements of the SC. We have generated transgenic mice expressing N- or C-terminal fluorescent-tagged SYCP3 (mCherry-SYCP3 (CSYCP) and SYCP3-mCherry (SYCPC)) to study SC dynamics and chromosome movements in vivo. Neither transgene rescued meiotic aberrations in Sycp3 knockouts, but CSYCP could form short axial element-like structures in the absence of endogenous SYCP3. On the wild-type background, both fusion proteins localized to the axes of the SC together with endogenous SYCP3, albeit with delayed initiation (from pachytene) in spermatocytes. Around 40% of CSYCP and SYCPC that accumulated on the SC was rapidly exchanging with other tagged proteins, as analyzed by fluorescent recovery after photobleaching (FRAP) assay. We used the CSYCP transgenic mice for further live cell analyses and observed synchronized bouquet configurations in living cysts of two or three zygotene oocyte nuclei expressing CSYCP, which presented cycles of telomere clustering and dissolution. Rapid chromosome movements were observed in both zygotene oocytes and pachytene spermatocytes, but rotational movements of the nucleus were more clear in oocytes. In diplotene spermatocytes, desynapsis was found to proceed in a discontinuous manner, whereby even brief chromosome re-association events were observed. Thus, this live imaging approach can be used to follow changes in the dynamic behavior of the nucleus and chromatin, in normal mice and different infertile mouse models.

Human male infertility and its genetic causes.

Background: Infertility affects about 15% of couples who wish to have children and half of these cases are associated with male factors. Genetic causes of azoospermia include chromosomal abnormalities, Y chromosome microdeletions, and specific mutations/deletions of several Y chromosome genes. Many researchers have analyzed genes in the AZF region on the Y chromosome; however, in 2003 the SYCP3 gene on chromosome 12 (12q23) was identified as causing azoospermia by meiotic arrest through a point mutation. Methods: We mainly describe the SYCP3 and PLK4 genes that we have studied in our laboratory, and add comments on other genes associated with human male infertility. Results: Up to now, The 17 genes causing male infertility by their mutation have been reported in human. Conclusions: Infertility caused by nonobstructive azoospermia (NOA) is very important in the field of assisted reproductive technology. Even with the aid of chromosomal analysis, ultrasonography of the testis, and detailed endocrinology, only MD-TESE can confirm the presence of immature spermatozoa in the testes. We strongly hope that these studies help clinics avoid ineffective MD-TESE procedures.

Single-molecule observation of DNA compaction by meiotic protein SYCP3.

In a previous paper (Syrjänen et al., 2014), we reported the first structural characterisation of a synaptonemal complex (SC) protein, SYCP3, which led us to propose a model for its role in chromosome compaction during meiosis. As a component of the SC lateral element, SYCP3 has a critical role in defining the specific chromosome architecture required for correct meiotic progression. In the model, the reported compaction of chromosomal DNA caused by SYCP3 would result from its ability to bridge distant sites on a DNA molecule with the DNA-binding domains located at each end of its strut-like structure. Here, we describe a single-molecule assay based on optical tweezers, fluorescence microscopy and microfluidics that, in combination with bulk biochemical data, provides direct visual evidence for our proposed mechanism of SYCP3-mediated chromosome organisation.