Expression of Rad51 and the histo-morphological evaluation of testis of the sterile male cattle-yak

Whole transcriptome sequencing revealed the gene regulatory network of hypoxic response in yak Sertoli cells

Yaks live in the Qinghai-Tibet Plateau for a long time where oxygen is scarce, but can ensure the smooth development of testis and spermatogenesis. The key lies in the functional regulation of the Sertoli cells under hypoxia. In this study, we sequenced yak Sertoli cells cultured in normal oxygen concentration (Normoxia) and treated with low oxygen concentration (Hypoxia) by whole transcriptomics, and screened out 194 differentially expressed mRNAs (DEmRNAs), 934 differentially expressed LncRNAs (DELncRNAs) and 129 differentially expressed miRNAs (DEmiRNAs). GO and KEGG analysis showed that these differential genes were mainly concentrated in PI3K-AKT, MAPK, RAS, and other signaling pathways, and were associated with glucose metabolism, tight junction, steroid hormone synthesis, cell fusion, and immunity of yak Sertoli cells. We constructed the gene interaction network of yak Sertoli cells in hypoxia and screened out the relationship pairs related to glucose metabolism and tight junction. The results suggested that the changes in energy metabolism, tight junction, and immune regulation of yak Sertoli cells under hypoxia might provide favorable conditions for spermatogenesis. This study provides data for further study on the role of non-coding RNA in testis development and spermatogenesis of yak.

Single-cell RNA sequencing and UPHLC-MS/MS targeted metabolomics offer new insights into the etiological basis for male cattle-yak sterility

The variety of species can be efficiently increased by interspecific hybridization. However, because the males in the hybrid progeny are usually sterile, this heterosis cannot be employed when other cattle and yaks are hybridized. While some system-level studies have sought to explore the etiological basis for male cattle-yak sterility, no systematic cellular analyses of this phenomenon have yet been performed. Here, single-cell RNA sequencing and UPHLC-MS/MS targeted metabolomics methods were used to study the differences in testicular tissue between 4-year-old male yak and 4-year-old male cattle-yak, providing new and comprehensive insights into the causes of male cattle-yak sterility. Cattle-yak testes samples detected 6 somatic cell types and one mixed germ cell type. Comparisons of these cell types revealed the more significant differences in Sertoli cells (SCs) and [Leydig cells and myoid cells (LCs_MCs)] between yak and cattle-yak samples compared to other somatic cell clusters. Even though the LCs and MCs from yaks and cattle-yaks were derived from the differentiation of the same progenitor cells, a high degree of overlap between LCs and MCs was observed in yak samples. Still, only a small overlap between LCs and MCs was observed in cattle-yak samples. Functional enrichment analyses revealed that genes down-regulated in cattle-yak SCs were primarily enriched in biological activity, whereas up-regulated genes in these cells were enriched for apoptotic activity. Furthermore, the genes of up-regulated in LCs_MCs of cattle-yak were significantly enriched in enzyme inhibitor and molecular function inhibitor activity. On the other hand, the genes of down-regulated in these cells were enriched for signal receptor binding, molecular function regulation, positive regulation of biological processes, and regulation of cell communication activity. The most significant annotated differences between yak and cattle-yak LCs_MCs were associated with cell-to-cell communication. While yak LCs_MCs regulated spermatogenic cells at spermatogonia, spermatocyte, and spermatid levels, no such relationships were found between cattle-yak LCs_MCs and germ cells. This may suggest that the somatic niche in male cattle-yak testes is a microenvironment that is ultimately not favorable for spermatogenesis.

Molecular cloning and expression analysis of rad51 gene associated with gametogenesis in Chinese soft-shell turtle (Pelodiscus sinensis)

Rad51 is a recA-like recombinase that plays a crucial role in repairing DNA double-strand breaks through homologous recombination during mitosis and meiosis in mammals and other organisms. However, its role in reptiles remains largely unclear. In this study, we aimed to investigate the physiological role of the rad51 gene in reptiles, particularly in Pelodiscus sinensis. Firstly, the cDNA of rad51 gene was cloned and analyzed in P. sinensis. The cloned cDNA contained an open reading frame (ORF) of 1020 bp and encodeed a peptide of 339 amino acids. The multiple alignments and phylogenetic tree analysis of Rad51 showed that P. sinensis shares the high identity with Chelonia mydas (97.95%) and Mus musculus (95.89%). Secondly, reverse transcription-polymerase chain reaction (RT-PCR) and real-time quantitative polymerase chain reaction (RT-qPCR) analysis showed that rad51 mRNA was highly expressed in both ovary and testis, while being weak in the somatic tissues examined in this study. Furthermore, chemical in situ hybridization (CISH) was performed to examine the expression profile of rad51 mRNA in germ cells at different stages. In the testis, rad51 mRNA expression was found to be stronger in the germ cells at early stages, specifically in spermatogonia and spermatocytes, but it was undetectable in spermatids. In the ovary, rad51 mRNA exhibited a uniform distribution in the cytoplasm of oocytes at early stages. The signal intensity of rad51 mRNA was highest in primary oocytes and gradually declined during oogenesis as the oocytes developed. These results suggest that rad51 plays a vital role in the development of germ cells, particularly during the early stages of gametogenesis in P. sinensis. The dynamic expression pattern of rad51 mRNA provides insights into the mechanisms underlying germ cell development and differentiation into gametes in turtles, even in reptiles.

Transcriptome analysis reveals dysregulated gene expression networks in Sertoli cells of cattle-yak hybrids

Cattle-yak, the hybrid offspring of yak and taurine cattle, exhibits male sterility with normal female fertility. Spermatogenesis is arrested in adult cattle-yak, and apoptosis is elevated in spermatogenic cells. Currently, the mechanisms underlying these defects remain elusive. Sertoli cells are the only somatic cells that directly interact with spermatogenic cells in the seminiferous tubules and play essential roles in spermatogenesis. The present study was designed to investigate gene expression signatures and potential roles of Sertoli cells in hybrid sterility in cattle-yak. Immunohistochemical analysis showed that the 5 mC and 5hmC signals in Sertoli cells of cattle-yaks were significantly different from those of age-matched yaks (P < 0.05). Transcriptome profiling of isolated Sertoli cells identified 402 differentially expressed genes (DEGs) between cattle-yaks and yaks. Notably, niche factor glial cell derived neurotrophic factor (GDNF) was upregulated, and genes involved in retinoic acid (RA) biogenesis were changed in Sertoli cells of cattle-yak, suggesting possible impairments of spermatogonial fate decisions. Further studies showed that the numbers of proliferative gonocytes and undifferentiated spermatogonia in cattle-yak were significantly higher than those in yak (P < 0.01). Exogenous GDNF significantly promoted the proliferation of UCHL1-positive spermatogonia in yaks. Therefore, we concluded that altered GDNF expression and RA signaling impacted the fate decisions of undifferentiated spermatogonia in cattle-yak. Together, these findings highlight the role of Sertoli cells and their derived factors in hybrid sterility.

Genetic variants underlying spermatogenic arrests in men with non-obstructive azoospermia

Spermatogenic arrest is a severe form of non-obstructive azoospermia (NOA), which occurs in 10-15% of infertile men. Interruption in spermatogenic progression at premeiotic, meiotic, or postmeiotic stage can lead to arrest in men with NOA. Recent studies have intensively focused on defining genetic variants underlying these spermatogenic arrests by making genome/exome sequencing. A number of variants were discovered in the genes involving in mitosis, meiosis, germline differentiation and other basic cellular events. Herein, defined variants in NOA cases with spermatogenic arrests and created knockout mouse models for the related genes are comprehensively reviewed. Also, importance of gene panel-based screening for NOA cases was discussed. Screening common variants in these infertile men with spermatogenic arrests may contribute to elucidating the molecular background and designing novel treatment strategies.

Localization and expression of SLX4 in the testis of sterile male cattle-yak

Cattle-yak, the hybrid offspring of yak (Bos grunniens) and cattle (Bos taurus), serves as a unique model to dissect the molecular mechanisms underlying reproductive isolation. While female cattle-yaks are fertile, the males are completely sterile due to spermatogenic arrest at the meiosis stage and massive germ cell apoptosis. Interestingly, meiotic defects are partially rescued in the testes of backcrossed offspring. The genetic basis of meiotic defects in male cattle-yak remains unclear. Structure-specific endonuclease subunit (SLX4) participates in meiotic double-strand break (DSB) formation in mice, and its deletion results in defects in spermatogenesis. In the present study, we examined the expression patterns of SLX4 in the testes of yak, cattle-yak, and backcrossed offspring to investigate its potential roles in hybrid sterility. The results showed that the relative abundances of SLX4 mRNA and protein were significantly reduced in the testis of cattle-yak. The results of immunohistochemistry revealed that SLX4 was predominately expressed in spermatogonia and spermatocytes. Chromosome spreading experiments showed that SLX4 was significantly decreased in the pachytene spermatocytes of cattle-yak compared with yak and backcrossed offspring. These findings suggest that SLX4 expression was dysregulated in the testis of cattle-yak, potentially resulting in the failure of crossover formation and collapses of meiosis in hybrid males.

Identification and profiling of microRNAs during yak's testicular development

BACKGROUND

Normal testicular development is highly crucial for male reproduction and is a precondition for spermatogenesis that is the production of spermatozoa in the testes. MiRNAs have been implicated in several testicular biological processes, including cell proliferation, spermatogenesis, hormone secretion, metabolism and reproductive regulation. In the present study, we used deep sequencing data to study the functions of miRNAs during testicular development and spermatogenesis, by analyzing the expression patterns of small RNAs in 6-, 18- and 30-month-old yak testis tissues.

RESULTS

A total of 737 known and 359 novel miRNAs were obtained from 6-, 18- and 30-month-old yak testes. In all, we obtained 12, 142 and 139 differentially expressed (DE) miRNAs in 30- vs. 18-, 18- vs. 6-, and 30- vs. 6-month-old testes, respectively. Gene Ontology (GO) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of all DE miRNA target genes revealed BMP2, TGFB2, GDF6, SMAD6, TGFBR2 and other target genes as participants in different biological processes, including TGF-β, GnRH, Wnt, PI3K-Akt, MAPK signaling pathways and several other reproductive pathways. In addition, quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) was used to detect the expression of seven randomly selected miRNAs in 6-, 18- and 30-month-old testes, and the results were consistent with the sequencing data.

CONCLUSIONS

The differential expression of miRNAs in yak testes at different development stages was characterized and investigated using deep sequencing technology. We believe that the results will contribute to further understanding the functions of miRNAs in regulating the development of yak testes and improving the reproductive performance of male yaks.

Increased double-strand breaks in aged mouse male germ cells may result from changed expression of the genes essential for homologous recombination or nonhomologous end joining repair

DNA double-strand breaks (DSBs) are commonly appearing deleterious DNA damages, which progressively increase in male germ cells during biological aging. There are two main pathways for repairing DSBs: homologous recombination (HR) and classical nonhomologous end joining (cNHEJ). Knockout and functional studies revealed that, while RAD51 and RPA70 proteins are indispensable for HR-based repair, KU80 and XRCC4 are the key proteins in cNHEJ repair. As is known, γH2AX contributes to these pathways through recruiting repair-related proteins to damaged site. The underlying reasons of increased DSBs in male germ cells during aging are not fully addressed yet. In this study, we aimed to analyze the spatiotemporal expression of the Rad51, Rpa70, Ku80, and Xrcc4 genes in the postnatal mouse testes, classified into young, prepubertal, pubertal, postpubertal, and aged groups according to their reproductive features and histological structures. We found that expression of these genes significantly decreased in the aged group compared with the other groups (P < 0.05). γH2AX staining showed that DSB levels in the germ cells from spermatogonia to elongated spermatids as well as in the Sertoli cells remarkably increased in the aged group (P < 0.05). The RAD51, RPA70, KU80, and XRCC4 protein levels exhibited predominant changes in the germ and Sertoli cells among groups (P < 0.05). These findings suggest that altered expression of the Rad51, Rpa70, Ku80, and Xrcc4 genes in the germ and Sertoli cells may be associated with increasing DSBs during biological aging, which might result in fertility loss.

Expression and Localization of Fas-Associated Factor 1 in Testicular Tissues of Different Ages and Ovaries at Different Reproductive Cycle Phases of Bos grunniens

Fas-associated factor 1 (FAF1), a member of the Fas family, is involved in biological processes such as apoptosis, inflammation, cell proliferation and proteostasis. This study aimed to explore the biological role of FAF1 in testicular tissue at different ages (juveniles (1 and 2 years old), adults (3, 4, 6, and 7 years old) and old-aged animals (11 years old)) and ovaries during different reproductive cycle phases (follicular, luteal, and pregnancy phases). FAF1 mRNA, relative protein expression and protein expression localization were determined in testes and ovaries using real-time quantification, WB and immunohistochemistry (IHC), respectively. Real-time quantification of testis tissues showed that the relative expression of FAF1 mRNA in testis tissues at 3, 4 and 7 years of age was significantly higher than of those in other ages, and in ovarian tissues was significantly higher in luteal phase ovaries than those in follicular and pregnancy phase ovaries; follicular phase ovaries were the lowest. WB of testis tissues showed that the relative protein expression of FAF1 protein was significantly higher at 11 and 7 years of age; in ovarian tissue, the relative protein expression of FAF1 protein was significantly higher in follicular phase ovaries than in luteal and pregnancy phase ovaries, and lowest in luteal phase ovaries. The relative protein expression of FAF1 at 3, 4 and 7 years of age was the lowest. IHC showed that FAF1 was mainly expressed in spermatozoa, spermatocytes, spermatogonia and supporting cells; in ovarian tissue, FAF1 was expressed in ovarian germ epithelial cells, granulosa cells, cumulus cells and luteal cells. The IHC results showed that FAF1 mRNA and protein were significantly differentially expressed in testes of different ages and ovarian tissues of different reproductive cycle phases, revealing the significance of FAF1 in the regulation of male and female B. grunniens reproductive physiology. Furthermore, our results provide a basis for the further exploration of FAF1 in the reproductive physiology of B. grunniens.

F1 Male Sterility in Cattle-Yak Examined through Changes in Testis Tissue and Transcriptome Profiles

Simple Summary

Cattle-yak, a crossbreed of cattle and yak, has evident heterosis but F1 male cattle-yak is unable to generate sperm and is sterile, which limits the fixation of heterosis. This study analyzed the differences in testicular tissue development between four-year-old yak and cattle-yak from the perspective of histomorphological changes and sequenced the testicular tissue of the two using RNA-seq technology, examining the differential gene expression related to spermatogenesis and apoptosis. These findings offer a theoretical explanation for the sterility in F1 male cattle-yak that can help yak hybridization.

Abstract

Male-derived sterility in cattle-yaks, a hybrid deriving from yak and cattle, is a challenging problem. This study compared and analyzed the histomorphological differences in testis between sexually mature yak and cattle-yak, and examined the transcriptome differences employing RNA-seq. The study found that yak seminiferous tubules contained spermatogenic cells at all levels, while cattle-yak seminiferous tubules had reduced spermatogonia (SPG) and primary spermatocyte (Pri-SPC), fewer secondary spermatocytes (Sec-SPC), an absence of round spermatids (R-ST) and sperms (S), and possessed large vacuoles. All of these conditions could have significantly reduced the volume and weight of cattle-yak testis compared to that of yak. RNA-seq analysis identified 8473 differentially expressed genes (DEGs; 3580 upregulated and 4893 downregulated). GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) enrichment evaluations for DEGs found their relation mostly to spermatogenesis and apoptosis. Among the DEGs, spermatogonia stem cell (SSCs) marker genes (Gfra1, CD9, SOHLH1, SALL4, ID4, and FOXO1) and genes involved in apoptosis (Fas, caspase3, caspase6, caspase7, caspase8, CTSK, CTSB and CTSC) were significantly upregulated, while differentiation spermatogenic cell marker genes (Ccna1, PIWIL1, TNP1, and TXNDC2) and meiosis-related genes (TEX14, TEX15, MEIOB, STAG3 and M1AP) were significantly downregulated in cattle-yak. Furthermore, the alternative splicing events in cattle-yak were substantially decreased than in yak, suggesting that the lack of protein subtypes could be another reason for spermatogenic arrest in cattle-yak testis.

The exploration of miRNAs and mRNA profiles revealed the molecular mechanisms of cattle-yak male infertility

Cattle-yak, the first-generation offspring of cattle and yak, inherited many excellent characteristics from their parents. However, F1 male hybrid infertility restricts the utilization of heterosis greatly. In this study, we first compared the testicular tissue histological characteristics of three cattle, three yaks, and three cattle-yak. Then we explored the miRNA profiles and the target functions of nine samples with RNA-seq technology. We further analyzed the function of DE gene sets of mRNA profiles identified previously with GSEA. Testicular histology indicated that the seminiferous tubules became vacuolated and few active germ cells can be seen. RNA-seq results showed 47 up-regulated and 34 down-regulated, 16 up-regulated and 21 down-regulated miRNAs in cattle and yaks compared with cattle-yak, respectively. From the intersection of DE miRNAs, we identified that bta-miR-7 in cattle-yak is down-regulated. Target prediction indicated that the filtered genes especially MYRFL, FANCA, INSL3, USP9X, and SHF of bta-miR-7 may play crucial roles in the reproductive process. With further network analysis and GSEA, we screened such hub genes and function terms, we also found some DE gene sets that enriched in ATP binding, DNA binding, and reproduction processes. We concluded that bta-miR-7 may play an important role in influencing fecundity. Our study provides new insights for explaining the molecular mechanism of cattle-yak infertility.

DNA methylome of primary spermatocyte reveals epigenetic dysregulation associated with male sterility of cattleyak

DNA cytosine methylation modification in the germline is of particular importance since it is a highly heritable epigenetic mark. Although cytosine methylation has been analyzed at the genome-scale for several mammalian species, our knowledge of DNA methylation patterns and the mechanisms underlying male hybrid sterility is still limited in domestic animals such as cattleyak. Here we for the first time show the genome-wide and single-base resolution landscape of methylcytosines (mC) in the primary spermatocyte (PSC) genome of yak with normal spermatogenesis and the inter-specific hybrid cattleyak with male infertility. A comparative investigation revealed that widespread differences are observed in the composition and patterning of DNA cytosine methylation between the two methylomes. Global CG or non-CG DNA methylation levels, as well as the number of mC sites, are increased in cattleyak compared to yak. Notably, the DNA methylome in cattleyak PSC exhibits promoter hypermethylation of meiosis-specific genes and piRNA pathway genes with respect to yak. Furthermore, major retrotransposonson classes are predominantly hypermethylated in cattleyak while those are fully hypomethylated in yak. KEGG pathway enrichment indicates Rap1 signaling and MAPK pathways may play potential roles in the spermatogenic arrest of cattleyak. Our present study not only provides valuable insights into distinct features of the cattleyak PSC methylome but also paves the way toward elucidating the complex, yet highly coordinated epigenetic modification during male germline development for inter-specific hybrid animals.

Histology study and transcriptome analysis of the testis of Loach(Misgurnus anguillicaudatus) in response to phenanthrene exposure

Phenanthrene (PHE) is one of the most abundant polycyclic aromatic hydrocarbon compounds (PAHs) in the aquatic environment. The loaches were exposed at concentrations of 0.30、1.00、3.00 mg L^-1 for 60 days. The effects of PHE on the testis development were evaluated by calculating the survival rate, observing the structure of testis and analyzing transcriptome. Firstly, PHE markedly decreased the survival rate in a dose-dependent manner. Then, the number and density of spermatogonia, primary spermatocytes, secondary spermatocytes and spermatids were substantially reduced under PHE exposure. The space in the seminiferous tubule obviously increased in the high PHE concentration group. Meanwhile, transcriptome comparative analysis identified 5329 differentially expressed genes (DEGs) including 2928 up-regulated and 2401 down-regulated in the testis of loach exposed PHE for 60 days. Meiotic cell cycle, arganelle fission, ATPase activity and adenylate nucleotide binding were significantly differences by GO (Gene Ontology) enrichment. KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway analysis revealed that TNF (Tumor Necrosis Factor) signaling pathway, CAMs (Cell Adhesion Molecules), cytochrome P450 and lipid metabolism were markedly regulated. In addition, eight DEGs were randomly selected from the testis transcriptomics results for qPCR verification, the results were consistent with RNA-Seq. Finally, related genes (piwil2, dmc1, vasa, ubr2, dnd, rnf17, plcb2, c-fos, gpx4) of testis development were further confirmed and they were differentially regulated after PHE exposure. In summary, a survey of the mechanism of loach testis response to PHE was performed, and a large number of gene expression levels regarding metabolism, spermatogenesis and immunity genes were acquired from RNA-seq. This study provide informations for elucidating the molecular mechanism of PHE affected the testis development of loach.

Characterization of N6-methyladenosine in cattle-yak testis tissue

N⁶-methyladenosine (m⁶A) is the most common form of eukaryotic mRNA modification, and it has been shown to exhibit broad regulatory activity in yeast, plants, and mammals. The specific role of m⁶A methylation as a regulator of spermatogenesis, however, has yet to be established. In this experiment, through a series of preliminary studies and methylated RNA immunoprecipitation sequencing, the m⁶A map of cattle-yak testicular tissue was established as a means of exploring how m⁶A modification affects cattle-yak male infertility. Cattle-yak testis tissues used in this study were found to contain sertoli cells and spermatogonia. Relative to sexually mature yak samples, those isolated from cattle-yak testis exhibited slightly reduced levels of overall methylation, although these levels were significantly higher than those in samples from pre-sexually mature yaks. Annotation analyses revealed that differentially methylated peaks were most concentrated in exonic regions, with progressively lower levels of concentration in the 3'-untranslated region (UTR) and 5'-UTR regions. To further explore the role of such m⁶A modification, enrichment analyses were performed on differentially methylated and differentially expressed genes in these samples. For the cattle-yaks vs. 18-months-old yaks group comparisons, differentially methylated genes were found to be associated with spermatogenesis-related GO terms related to the cytoskeleton and actin-binding, as well as with KEGG terms related to the regulation of the actin cytoskeleton and the MAPK signaling pathway. Similarly, enrichment analyses performed for the cattle-yaks vs. 5-years-old yaks comparison revealed differentially methylated genes to be associated with GO terms related to protein ubiquitination, ubiquitin ligase complexes, ubiquitin-dependent protein catabolism, and endocytotic activity, as well as with KEGG terms related to apoptosis and the Fanconi anemia pathway. Overall, enrichment analyses for the cattle-yaks vs. 18-months-old yaks comparison were primarily associated with spermatogenesis, whereas those for the cattle-yaks vs. 5-years-old yaks comparison were primarily associated with apoptosis.

Disruption of cell proliferation and apoptosis balance in the testes of crossbred cattle-yaks affects spermatogenic cell fate and sterility

The balance between proliferation, differentiation, and apoptosis is well-coordinated in spermatogenesis for the timely production of appropriate numbers of sperm in animals. Disruption or decrease in sperm production is due to many conditions, including changes in testicular cell fate balance. Interspecies hybridisation of domestic yaks and cattle results in sterility in males because of spermatogenic arrest; however, the underlying mechanisms involved in sterility are still unclear. In the present study, we investigated the proliferation and apoptosis status during the development of yaks and crossbred cattle-yaks using immunohistochemistry of proliferating cell nuclear antigen and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assays. Testicular tissues from yaks (immature: 1 year old, mature: 2-3 years old) and backcrossed hybrids (2 year old) were collected and used to investigate the expression of each parameter in testicular cells. During the maturation of yak testes, proliferation and apoptosis became active only in spermatogenic cells, and not in other somatic cells, such as Sertoli cells, myoid cells, and Leydig cells. Furthermore, hybrid cattle-yak testes maintained proliferation ability but less apoptotic ability in spermatogenic cells when compared to yaks of the same age, suggesting that normal spermatogenic cell fate control is disrupted by changes in the balance between proliferation and apoptosis. In addition, Leydig cell proliferation rate was higher than apoptosis rate in the cattle-yak testes, indicating an increased number of Leydig cells, which may affect spermatogenesis through changes in steroidogenesis. Although epigenetic changes may be involved in cattle-yak testes, further studies are needed to clarify the modulation of proliferation and apoptosis to elucidate the mechanisms of infertility in hybrid cattle-yak males.