Conversion from mitosis to meiosis: morphology and expression of proliferating cell nuclear antigen (PCNA) and Dmc1 during newt spermatogenesis

Identification, Characterization and Functional Analysis of Fibroblast Growth Factors in Black Rockfish (Sebastes schlegelii)

Fibroblast growth factors (FGFs) are short polypeptides that play essential roles in various cellular biological processes, including cell migration, proliferation, and differentiation, as well as tissue regeneration, immune response, and organogenesis. However, studies focusing on the characterization and function of FGF genes in teleost fishes are still limited. In this study, we identified and characterized expression patterns of 24 FGF genes in various tissues of embryonic and adult specimens of the black rockfish (Sebates schlegelii). Nine FGF genes were found to play essential roles in myoblast differentiation, as well as muscle development and recovery in juvelines of S. schlegelii. Moreover, sex-biased expression pattern of multiple FGF genes was recorded in the species' gonads during its development. Among them, expression of the FGF1 gene was recorded in interstitial and sertoli cells of testes, promoting germ-cell proliferation and differentiation. In sum, the obtained results enabled systematic and functional characterization of FGF genes in S. schlegelii, laying a foundation for further studies on FGF genes in other large teleost fishes.

Simple, once-off mapping of various, recurrent immunostaining patterns of proliferating cell nuclear antigen in spermatogonia at the immature pole of the testis of adult wild-caught blue shark, Prionace glauca: Correlations with changes in testicular status

This study was a single time-point mapping of various immunostaining patterns revealed with the proliferating cell nuclear antigen (PCNA) PC10 antibody in spermatogonia at the immature pole of the testis of the Blue shark (Prionace glauca). Scattered in the stroma of the germinal ridge that demarcates the immature pole's outer boundary were nests of variously immunoreactive A-spermatogonia, each flanked by a fusiform cell. Spermatocysts were assembled from niche-derived stromal cells, displaced A-progenitors, and their progeny, which showed one of two main immunostaining patterns (i.e., an uneven light brown/globular and homogeneous dark [hod] brown appearance). The testes of wild-caught Prionace showed two conditions, namely, extensive multinucleate cell death (MNC) near the mitosis-meiosis transition or an early recovery phase from the latter showing vacuolated areas. Both the proportion of cysts with immature B^hod -spermatogonia and the frequency of mitotic figures in such cysts in the early recovery testis condition were significantly higher than the comparable parameters in MNC testis condition. Moreover, the post-MNC recovery phase revealed a decrease in the proportion of immature cysts with uneven light brown/globular-like spermatogonia. The protracted spread of a cell cycle signal in an anatomically discrete, syncytially connected spermatogonial clone manifests as different PCNA immunoreactivities.

Excessive unilateral proliferation of spermatogonia in a patient with non-obstructive azoospermia - adverse effect of clomiphene citrate pre-treatment?

Background

Clomiphene citrate has been proposed as pre-treatment for infertile men with non-obstructive, testicular azoospermia (NOA) before surgery for testicular sperm extraction (TESE), especially when serum testosterone is low.

Case presentation

Here, we report on a 33-year old azoospermic patient with a previous history of repeated "fresh" TESE and clomiphene citrate therapy (50 mg/day over 6 months) before undergoing microscopically assisted, bilateral testicular biopsy. Comprehensive histological and immunohistochemical work-up revealed a heterogeneous spermatogenic arrest at the level of spermatogonia or primary spermatocytes, with focally preserved spermatogenesis up to elongated spermatids in the right testis. In the left testis, the majority of tubules (> 70%) showed no tubular lumen or regular seminiferous epithelium but a great number of spermatogonia-like cells. These cells proved to be normally differentiated spermatogonia (positive for melanoma associated antigen 4 (MAGEA4), negative for placental alkaline phosphatase (PlAP)) with increased proliferative activity (positive for proliferating cell nuclear antigen (PCNA)) and a slightly higher rate of apoptotic cells. When compared to a tissue control with normal spermatogenesis, expression of sex hormone receptors androgen receptor (AR), estrogen receptor (ER) alpha, and G-protein coupled estrogen receptor 1 (GPER1) was not altered in patient samples. Sertoli cells appeared to be mature (positive for vimentin, negative for cytokeratin 18), whereas the expression of zona occludens protein 1 (ZO-1), claudin 11, and connexin 43 was absent or dislocated in the tubules with abundance of spermatogonia.

Conclusion

This result suggests that formation of the blood-testis barrier is disturbed in affected tubules. To our knowledge this is the first observation of excessive, non-malignant proliferation of spermatogonia in a NOA patient. Although underlying molecular mechanisms remain to be elucidated, we hypothesize that the unusual pathology was triggered by the high-dose clomiphene citrate treatment preceding testicular biopsy.

Human X chromosome exome sequencing identifies BCORL1 as contributor to spermatogenesis

BACKGROUND

Infertility affects approximately 15% of couples worldwide with male infertility being responsible for approximately 50% of cases. Although accumulating evidence demonstrates the critical role of the X chromosome in spermatogenesis during the last few decades, the expression patterns and potential impact of the X chromosome, together with X linked genes, on male infertility are less well understood.

METHODS

We performed X chromosome exome sequencing followed by a two-stage independent population validation in 1333 non-obstructive azoospermia cases and 1141 healthy controls to identify variant classes with high likelihood of pathogenicity. To explore the functions of these candidate genes in spermatogenesis, we first knocked down these candidate genes individually in mouse spermatogonial stem cells (SSCs) using short interfering RNA oligonucleotides and then generated candidate genes knockout mice by CRISPR-Cas9 system.

RESULTS

Four low-frequency variants were identified in four genes (BCORL1, MAP7D3, ARMCX4 and H2BFWT) associated with male infertility. Functional studies of the mouse SSCs revealed that knocking down Bcorl1 or Mtap7d3 could inhibit SSCs self-renewal and knocking down Armcx4 could repress SSCs differentiation in vitro. Using CRISPR-Cas9 system, Bcorl1 and Mtap7d3 knockout mice were generated. Excitingly, Bcorl1 knockout mice were infertile with impaired spermatogenesis. Moreover, Bcorl1 knockout mice exhibited impaired sperm motility and sperm cells displayed abnormal mitochondrial structure.

CONCLUSION

Our data indicate that the X-linked genes are associated with male infertility and involved in regulating SSCs, which provides a new insight into the role of X-linked genes in spermatogenesis.

NMDA-type glutamate receptors mediate the acrosome reaction and motility initiation in newt sperm

The N-methyl d-aspartate type glutamate receptor (NMDAR) is a ligand-gated cation channel that causes Ca²⁺ influx in nerve cells. An NMDAR agonist is effective to the sperm motility in fowls, although the actual role of NMDAR in sperm function is unknown. In the present study, RNA-seq of the spermatogenic testes suggested the presence of NMDAR in the sperm of the newt Cynops pyrrhogaster. Glutamate of at least 0.7 ± 0.5 mM was detected in the egg-jelly substances along with acrosome reaction-inducing substance (ARIS) and sperm motility-initiating substance (SMIS). In the egg-jelly extract (JE) that included the ARIS and SMIS, the acrosome reaction was inhibited by a NMDAR antagonists, memantine and MK801. MK801 also inhibited the spontaneous acrosome reaction in Steinberg's salt solution (ST). Furthermore, memantine and MK801 suppressed the progressive motility of the sperm in JE and spontaneous waving of the undulating membrane, which is the tail structure giving thrust for forward motility, in ST. The spontaneous waving of the undulating membrane was promoted when Mg²⁺ , which blocks Ca²⁺ influx through gated NMDARs, was removed from the ST. In addition, the ARIS-induced acrosome reaction was inhibited by a selective antagonist of the transient receptor potential vanilloid 4, whose activation might result in the membrane depolarization to release Mg²⁺ from the NMDAR. These results suggest that NMDAR acts together with other cation channels in the induction of the acrosome reaction and motility of the sperm during the fertilization process of C. pyrrhogaster.

CD49f-positive testicular cells in Saanen dairy goat were identified as spermatogonia-like cells by miRNA profiling analysis

miRNAs, a type of small RNA, play critical roles in mammalian spermatogenesis. Spermatogonia are the foundation of spermatogenesis and are valuable for the study of spermatogenesis. However, the expression profiling of the miRNAs in spermatogonia of dairy goats remains unclear. CD49f has been one of the surface markers used for spermatogonia enrichment by magnetic activated cell sorting (MACS). Therefore, we used a CD49f microbead antibody to purify CD49f-positive and -negative cells of dairy goat testicular cells by MACS and then analysed the miRNA expression in these cells in depth using Illumina sequencing technology. The results of miRNA expression profiling in purified CD49f-positive and -negative testicular cells showed that 933 miRNAs were upregulated in CD49f-positive cells and 916 miRNAs were upregulated in CD49f-negative cells with a twofold increase, respectively; several miRNAs and marker genes specific for spermatogonial stem cells (SSCs) in testis had a higher expression level in CD49f-positive testicular cells, including miR-221, miR-23a, miR-29b, miR-24, miR-29a, miR-199b, miR-199a, miR-27a, and miR-21 and CD90, Gfra1, and Plzf. The bioinformatics analysis of differently expressed miRNAs indicated that the target genes of these miRNAs in CD49f-positive cells were involved in cell-cycle biological processes and the cell-cycle KEGG pathway. In conclusion, our comparative miRNAome data provide useful miRNA profiling data of dairy goat spermatogonia cells and suggest that CD49f could be used to enrich dairy goat spermatogonia-like cells, including SSCs.

An ENU-induced mutation in the mouse Rnf212 gene is associated with male meiotic failure and infertility

The ENU-induced repro57 mutation was identified in an unbiased screen for the discovery of novel genes for fertility. Male repro57 homozygous mice are infertile and exhibit significantly reduced testis weight compared with WT mice. Histological examination of mutant testes revealed that spermatocytes degenerated during late prophase, and no mature spermatozoa were found in the seminiferous epithelium, suggesting that infertility is caused by the arrest of spermatogenesis at late meiotic prophase. Consistent with this hypothesis, the number of foci with MLH1, a protein essential for crossing over, is greatly reduced in repro57 mutant spermatocytes, which also lack chiasmata between homologs and exhibit premature dissociation of XY chromosomes. In repro57 mutant mice, we identified a mutation in the Rnf212 gene, encoding Ring finger protein 212. The overall phenotype of repro57 mice is consistent with the recently reported phenotype of the Rnf212 knockout mice; slight differences may be due to genetic background effects. Thus, the repro57 nonsense mutation provides a new allele of the mouse Rnf212 gene.

Senataxin plays an essential role with DNA damage response proteins in meiotic recombination and gene silencing

Senataxin, mutated in the human genetic disorder ataxia with oculomotor apraxia type 2 (AOA2), plays an important role in maintaining genome integrity by coordination of transcription, DNA replication, and the DNA damage response. We demonstrate that senataxin is essential for spermatogenesis and that it functions at two stages in meiosis during crossing-over in homologous recombination and in meiotic sex chromosome inactivation (MSCI). Disruption of the Setx gene caused persistence of DNA double-strand breaks, a defect in disassembly of Rad51 filaments, accumulation of DNA:RNA hybrids (R-loops), and ultimately a failure of crossing-over. Senataxin localised to the XY body in a Brca1-dependent manner, and in its absence there was incomplete localisation of DNA damage response proteins to the XY chromosomes and ATR was retained on the axial elements of these chromosomes, failing to diffuse out into chromatin. Furthermore persistence of RNA polymerase II activity, altered ubH2A distribution, and abnormal XY-linked gene expression in Setx^−/− revealed an essential role for senataxin in MSCI. These data support key roles for senataxin in coordinating meiotic crossing-over with transcription and in gene silencing to protect the integrity of the genome.

Ataxia with oculomotor apraxia type 2 (AOA2) caused by a defect in the gene Setx (coding for senataxin) is part of a subgroup of autosomal recessive ataxias characterized by defects in genes responsible for the recognition and/or repair of damage in DNA. Cells from these patients are characterized by oxidative stress and are defective in RNA processing and termination of transcription. Recent data suggest that senataxin is involved in coordinating events between DNA replication forks and ongoing transcription. To further understand the role of senataxin, we disrupted the Setx gene in mice and demonstrated its essential role in spermatogenesis during meiotic recombination and in meiotic sex chromosome inactivation (MSCI). In the absence of senataxin, DNA double-strand breaks persist, RNA:DNA hybrids (R-loops) accumulate, and homologous recombination is disrupted. Senataxin localised to the XY chromosomes during pachytene. This was dependent on Brca1, which functions early in MSCI to recruit DNA damage response proteins to the XY body. In the absence of senataxin, there was incomplete accumulation of DNA damage response proteins on the XY chromosomes and no MDC1-dependent diffusion of ATR to the broader XY chromatin. The end result was a defect in MSCI, apoptosis, and a failure to complete meiosis.

Molecular cloning of proliferating cell nuclear antigen and its differential expression analysis in the developing ovary and testis of penaeid shrimp Marsupenaeus japonicus

To understand the molecular mechanisms of gonadal development and maturation in penaeid shrimp Marsupenaeus japonicus, eight differentially expressed genes were obtained using a modified annealing control primer system. One of these genes is a proliferating cell nuclear antigen (PCNA). Bioinformatics analyses showed that full-length cDNA of M. japonicus PCNA (mjPCNA) consists of 75 bp of 5' untranslated region, 783 bp of coding region, and 65 bp of 3' untranslated region (excluding the polyA tail), encoding a protein of 260 amino acids with a predicted molecular mass of 28.85 kDa and an isoelectric point of 4.59. Real-time polymerase chain reaction analyses demonstrated that the gene expression level changed significantly in the developing testis and ovary. In stage 1 of ovary and testis, mjPCNA showed its lowest level during development and reached its highest expression level in stage 2 of ovary and testis. In stages 4 and 5 of ovary and the stage 3 of testis, mjPCNA held a steady expression level. Data suggest that PCNA plays an important role in the testis and ovary development, especially in the process of mitosis and meiosis.

Lifelong testicular differentiation in Pleurodeles waltl (Amphibia, Caudata)

BACKGROUND

In numerous Caudata, the testis is known to differentiate new lobes at adulthood, leading to a multiple testis. The Iberian ribbed newt Pleurodeles waltl has been studied extensively as a model for sex determination and differentiation. However, the evolution of its testis after metamorphosis is poorly documented.

METHODS

Testes were obtained from Pleurodeles waltl of different ages reared in our laboratory. Testis evolution was studied by several approaches: morphology, histology, immunohistochemistry and RT-PCR. Surgery was also employed to study testis regeneration.

RESULTS

In this species, the testis is linked to the lung. This association consists of connective tissue derived from the mesorchium and the coelomic epithelium surrounding the lung and takes place at the end of larval life. This tissue contains lobules including primordial germ cells with a typical large and polylobular nucleus. The anterior part of the testis remains thin and undifferentiated while the posterior part differentiates in a large first testis lobe where spermatogenesis occurs during the first year of life. The undifferentiated status of the anterior part is attested by the lack of expression of the testis marker Dmrt1 and the meiosis entry marker Dmc1. Three-year-old Pleurodeles waltl possess multiple testes made up of two lobes. The second lobe appears at the caudal extremity of the first one from residual primordial germ cells located near or even inside efferent ducts in the glandular tissue that usually appears following spermatozoa extrusion. Surprisingly, in the case of surgical elimination of the anterior part of the testis, de novo spermatogenesis is stopped in the first lobe which becomes restricted to the glandular tissue. Following first testis lobe removal, the anterior part of the testis regenerates a new testis lobe, a process stimulated in the presence of DHT.

CONCLUSION

Pleurodeles waltl constitute an original gonochoristic vertebrate model in which testis differentiation is observed up to adulthood.

Molecular cloning and gene expression of Spo11 during spermatogenesis in the Japanese eel, Anguilla japonica

Spo11 is a protein involved specifically in the meiotic recombination in several species, however, it is little characterized in lower vertebrates. We identified a cDNA encoding Spo11 from the testis of Japanese eel, Anguilla japonica. The deduced amino acid sequence of eel Spo11 was more than 60% identical with human and mouse Spo11s. In order to examine changes in the expression and localization of Spo11 during spermatogenesis induced by the injection of human chorionic gonadotropin (hCG) and to compare with those of Dmc1, we generated specific antibodies against the eel Spo11 and Dmc1. In general, it is believed that Dmc1 is a meiosis-specific protein, and the localization of Dmc1 in spermatocytes was confirmed also in Japanese eel. Spo11 transcripts were slightly detected in the testis after 1 day post-hCG injection by Northern blot analysis. Western blot analysis also indicated that Spo11 production began at day 1 after hCG injection. However, immunohistochemical observations showed that Spo11 was localized only in spermatocytes. In contrast, Dmc1 transcripts and the protein production were first detected at day 6 after hCG injection and increased along with the increment of spermatocytes. These results suggested that Spo11 was expressed in spermatogonia proliferated toward meiosis at quite low level that could not induce meiotic recombination, thereafter Spo11 expression increased and Dmc1 expression was initiated in early meiotic prophase. Hence, the antibodies against eel Spo11 and Dmc1 generated in the present study can be use to detect germ cells in early meiotic prophase immunohistochemically. Importantly, it is suggested that germ cells, which are in quite earlier stage during meiotic prophase, can be detected by Spo11.

Evidence for biological rhythm in spermatogenesis in the pubertal hamster (Mesocricetus auratus): a flow cytometric study

The number of cells in the S-phase fraction of the cell cycle reflects proliferative activity. Using flow cytometry histograms and the Phoenix M+ cell cycle program, the percent of cells in the S-phase fraction was measured in single cell suspensions prepared from testes of hamsters of different ages. A cyclical pattern with a period of 9 days, superimposed on another rhythm with a 38 day period was observed (p < 0.01) during hamster maturation and it disappeared after the second spermatogenic wave, where the S phase values reached a plateau. It was concluded that maturing animals passed through a stage in which testicular biological rhythm was involved. Therefore it was concluded that it takes approximately two spermatogenic waves before the proliferation rate in the testis reached a steady state.

Abnormal spermatogenesis at low temperatures in the Japanese red-bellied newt, Cynops pyrrhogaster: possible biological significance of the cessation of spermatocytogenesis

In newt testis, spermatocytes never appear during winter, because secondary spermatogonia die by apoptosis just before meiosis. In the current study, we examined the effect of low temperatures on spermatogenesis. Incubation of newts at low temperatures (8, 12, 15 degrees C) induced defects in spermatogenesis in a temperature-dependent manner. At 8 degrees C, multinucleated giant cells (MGCs) were observed in spermatocytes and spermatogenesis never proceeded beyond meiosis. Although spermatocytes completed meiotic divisions at 12 degrees C, severe cell death was observed in the spermatids. At 15 degrees C both normal and abnormal spermiogenesis were observed. Under these conditions, impaired meiotic synapsis/recombination and down-regulation of the expression of the DMC1 protein, which play pivotal roles in meiotic pairing in eukaryotes, were also observed. Furthermore, to examine the quality of the sperm produced at low temperature for supporting development, artificial insemination was performed. The eggs inseminated with spermatozoa derived from newts kept at 15 degrees C demonstrated a restricted developmental capacity, even though these spermatozoa had an equal capacity for carrying out fertilization to those kept at 22 degrees C. These results suggest that meiosis at low temperatures cause the production of abnormal spermatozoa. Conservation and the significance of this phenomenon in poikilothermic vertebrates living in the temperate zones are also discussed.

Follicle-stimulating hormone is indispensable for the last spermatogonial mitosis preceding meiosis initiation in newts (Cynops pyrrhogaster)

We previously reported that mammalian FSH induced differentiation of secondary spermatogonia into primary spermatocytes in organ culture of newt testicular fragments, whereas in medium lacking FSH primary spermatocytes never appeared. Here, we investigated why spermatogonia fail to form primary spermatocytes in the absence of FSH. Spermatogonia maintained proliferative activity and viability at about half the level of those cultured in the presence of FSH, progressed into the seventh generation, but became moribund during the G2/M phase. Thus, the eighth generation of spermatogonia never appeared, suggesting that cell death is the chief reason why primary spermatocytes fail to form in the absence of FSH. The presence of Dmc1, a molecular marker for the spermatocyte stage, confirmed our microscopic observations that spermatogonia differentiated into primary spermatocytes in the presence of FSH. Thus, FSH is indispensable for the completion of the last spermatogonial mitosis, a prerequisite for the conversion of germ cells from mitosis to meiosis. Because prolactin induced apoptosis in spermatogonia during the seventh generation, we propose that a checkpoint exists for the initiation of meiosis in the seventh generation whereby spermatogonia enter meiosis when the concentration ratio of FSH to prolactin is high but fail to do so when the ratio is low.