Comparison of Y-chromosome-linked TSPY, TSPY2, and PRAMEY genes in Taurus cattle, yaks, and interspecific hybrid bulls

mRNA-Seq of testis and liver tissues reveals a testis-specific gene and alternative splicing associated with hybrid male sterility in dzo

Alternative splicing (AS) plays an important role in the co-transcription and post-transcriptional regulation of gene expression during mammalian spermatogenesis. The dzo is the male F1 offspring of an interspecific hybrid between a domestic bull (Bos taurus ♂) and a yak (Bos grunniens ♀) which exhibits male sterility. This study aimed to identify the testis-specific genes and AS associated with hybrid male sterility in dzo. The iDEP90 program and rMATS software were used to identify the differentially expressed genes (DEG) and differential alternative splicing genes (DSG) based on RNA-seq data from the liver (n = 9) and testis (n = 6) tissues of domestic cattle, yak, and dzo. Splicing factors (SF) were obtained from the AmiGO2 and the NCBI databases, and Pearson correlation analysis was performed on the differentially expressed SFs and DSGs. We focused on the testis-specific DEGs and DSGs between dzo and cattle and yak. Among the top 3,000 genes with the most significant variations between these 15 samples, a large number of genes showed testis-specific expression involved with spermatogenesis. Cluster analysis showed that the expression levels of these testis-specific genes were dysregulated during mitosis with a burst downregulation during the pachynema spermatocyte stage. The occurrence of AS events in the testis was about 2.5 fold greater than in the liver, with exon skipping being the major AS event (81.89% to 82.73%). A total of 74 DSGs were specifically expressed in the testis and were significantly enriched during meiosis I, synapsis, and in the piRNA biosynthesis pathways. Notably, STAG3 and DDX4 were of the exon skipping type, and DMC1 was a mutually exclusive exon. A total of 36 SFs were significantly different in dzo testis, compared with cattle and yak. DDX4, SUGP1, and EFTUD2 were potential SFs leading to abnormal AS of testis-specific genes in dzo. These results show that AS of testis-specific genes can affect synapsis and the piRNA biosynthetic processes in dzo, which may be important factors associated with hybrid male sterility in dzo.

Whole-Genome Re-sequencing and Transcriptome Reveal Candidate Genes and Pathways Associated with Hybrid Sterility in Hermaphroditic Argopecten Scallops

The interspecific hybrid scallops generated from the hermaphroditic bay scallops (Argopecten irradians) and Peruvian scallops (Argopecten purpuratus) showed significant heterosis in growth. However, its sterility limits large-scale hybridization and hinders the development of the scallop breeding industry. Hybrid sterility is regulated by plenty of genes and involves a range of biochemical and physiological transformations. In this study, whole-genome re-sequencing and transcriptomic analysis were performed in sterile and fertile hybrid scallops. The potential genetic variations and abnormally expressed genes were detected to explore the mechanism underlying hybrid sterility in hermaphroditic Argopecten scallops. Compared with fertile hybrids, 24 differentially expressed genes (DEGs) with 246 variations were identified to be related to fertility regulation, which were mainly enriched in germarium-derived egg chamber formation, spermatogenesis, spermatid development, mismatch repair, mitotic and meiotic cell cycles, Wnt signaling pathway, MAPK signaling pathway, calcium modulating pathway, and notch signaling pathway. Specifically, variation and abnormal expression of these genes might inhibit the progress of mitosis and meiosis, promote cell apoptosis, and impede the genesis and maturation of gametes in sterile hybrid scallops. Eleven DEGs (XIAP, KAZN, CDC42, MEIS1, SETD1B, NOTCH2, TRPV5, M- EXO1, GGT1, SBDS, and TBCEL) were confirmed by qRT-PCR validation. Our findings may enrich the determination mechanism of hybrid sterility and provide new insights into the use of interspecific hybrids for extensive breeding.

Evaluation of MYBL1 as the master regulator for pachytene spermatocyte genes dysregulated in interspecific hybrid dzo

Misregulation of spermatogenesis transcription factors (TF) in hybrids can lead to misexpression, which is a mechanism for hybrid male sterility (HMS). We used dzo (male offspring of Bos taurus ♂ × Bos grunniens ♀) in bovines to investigate the relationship of the key TF with HMS via RNA sequencing and assay for transposase-accessible chromatin with high-throughput sequencing analyses. RNA sequencing showed that the widespread misexpression in dzo was associated with spermatogenesis-related genes and somatic or progenitor genes. The transition from leptotene or zygotene spermatocytes to pachytene spermatocytes may be the key stage for meiosis arrest in dzo. The analysis of TF-binding motif enrichment revealed that the male meiosis-specific master TF MYB proto-oncogene like 1 (MYBL1, known as A-MYB) motif was enriched on the promoters of downregulated pachytene spermatocyte genes in dzo. Assay for transposase-accessible chromatin with high-throughput sequencing revealed that TF-binding sites for MYBL1, nuclear transcription factor Y, and regulatory factor X were enriched in the low-chromatin accessibility region of dzo. The target genes of the MYBL1-binding motif were associated with meiosis-specific genes and significantly downregulated in dzo testis. The transcription factor MYBL1 may be the candidate master regulator for pachytene spermatocyte genes dysregulated in interspecific HMS dzo. This study reported that a few upstream TF regulation changes might exert a cascading effect downstream in a regulatory network as a mechanism for HMS.

Sexing of cattle embryos using RNA-sequencing data or polymerase chain reaction based on a complete sequence of cattle chromosome Y

When necessary, RNA-sequencing data or polymerase chain reaction (PCR) assays can be used to determine the presence of the chromosome Y (ChrY) in samples. This information allows for biological variation due to sexual dimorphism to be studied. A prime example is when researchers conduct RNA-sequencing of single embryos, or conceptuses, prior to the development of gonads. A recent publication of a complete sequence of the ChrY has removed limitations for the development of these procedures in cattle, otherwise imposed by the absence of a ChrY in the reference genome. Using the sequence of the cattle ChrY and transcriptome data, we conducted a systematic search for genes in the ChrY that are exclusively expressed in male tissues. The genes ENSBIXG00000029763, ENSBIXG00000029774, ENSBIXG00000029788, and ENSBIXG00000029892 were consistently expressed across male tissues and lowly expressed or absent in female samples. We observed that the cumulative values of counts per million were 2688-fold greater in males than the equivalent values in female samples. Thus, we deemed these genes suitable for the sexing of samples using RNA-sequencing data. We successfully used this set of genes to infer the sex of 22 cattle blastocysts (8 females and 14 males). Additionally, the completed sequence of the cattle ChrY has segments in the male-specific region that are not repeated. We designed a pair of oligonucleotides that targets one of these non-repeated regions in the male-specific sequence of the ChrY. Using this pair of oligonucleotides, in a multiplexed PCR assay with oligonucleotides that anneal to an autosome chromosome, we accurately identified the sex of cattle blastocysts. We developed efficient procedures for the sexing of samples in cattle using either transcriptome data or their DNA. The procedures using RNA-sequencing will greatly benefit researchers who work with samples limited in cell numbers which are only sufficient to produce transcriptome data. The oligonucleotides used for the accurate sexing of samples using PCR are transferable to other cattle tissue samples.

Testis-Specific Protein Y-Encoded (TSPY) Is Required for Male Early Embryo Development in Bos taurus

TSPY is a highly conserved multi-copy gene with copy number variation (CNV) among species, populations, individuals and within families. TSPY has been shown to be involved in male development and fertility. However, information on TSPY in embryonic preimplantation stages is lacking. This study aims to determine whether TSPY CNV plays a role in male early development. Using sex-sorted semen from three different bulls, male embryo groups referred to as 1Y, 2Y and 3Y, were produced by in vitro fertilization (IVF). Developmental competency was assessed by cleavage and blastocyst rates. Embryos at different developmental stages were analyzed for TSPY CN, mRNA and protein levels. Furthermore, TSPY RNA knockdown was performed and embryos were assessed as per above. Development competency was only significantly different at the blastocyst stage, with 3Y being the highest. TSPY CNV and transcripts were detected in the range of 20-75 CN for 1Y, 20-65 CN for 2Y and 20-150 CN for 3Y, with corresponding averages of 30.2 ± 2.5, 33.0 ± 2.4 and 82.3 ± 3.6 copies, respectively. TSPY transcripts exhibited an inverse logarithmic pattern, with 3Y showing significantly higher TSPY. TSPY proteins, detected only in blastocysts, were not significantly different among groups. TSPY knockdown resulted in a significant TSPY depletion (p < 0.05), with no development observed after the eight-cell stage in male embryos, suggesting that TSPY is required for male embryo development.

Copy number variation of horse Y chromosome genes in normal equine populations and in horses with abnormal sex development and subfertility: relationship of copy number variations with Y haplogroups

Structural rearrangements like copy number variations in the male-specific Y chromosome have been associated with male fertility phenotypes in human and mouse but have been sparsely studied in other mammalian species. Here, we designed digital droplet PCR assays for 7 horse male-specific Y chromosome multicopy genes and SRY and evaluated their absolute copy numbers in 209 normal male horses of 22 breeds, 73 XY horses with disorders of sex development and/or infertility, 5 Przewalski's horses and 2 kulans. This established baseline copy number for these genes in horses. The TSPY gene showed the highest copy number and was the most copy number variable between individuals and breeds. SRY was a single-copy gene in most horses but had 2-3 copies in some indigenous breeds. Since SRY is flanked by 2 copies of RBMY, their copy number variations were interrelated and may lead to SRY-negative XY disorders of sex development. The Przewalski's horse and kulan had 1 copy of SRY and RBMY. TSPY and ETSTY2 showed significant copy number variations between cryptorchid and normal males (P < 0.05). No significant copy number variations were observed in subfertile/infertile males. Notably, copy number of TSPY and ETSTY5 differed between successive male generations and between cloned horses, indicating germline and somatic mechanisms for copy number variations. We observed no correlation between male-specific Y chromosome gene copy number variations and male-specific Y chromosome haplotypes. We conclude that the ampliconic male-specific Y chromosome reference assembly has deficiencies and further studies with an improved male-specific Y chromosome assembly are needed to determine selective constraints over horse male-specific Y chromosome gene copy number and their relation to stallion reproduction and male biology.

Repetitive DNA Sequences in the Human Y Chromosome and Male Infertility

The male-specific Y chromosome, which is well known for its diverse and complex repetitive sequences, has different sizes, genome structures, contents and evolutionary trajectories from other chromosomes and is of great significance for testis development and function. The large number of repetitive sequences and palindrome structure of the Y chromosome play an important role in maintaining the stability of male sex determining genes, although they can also cause non-allelic homologous recombination within the chromosome. Deletion of certain Y chromosome sequences will lead to spermatogenesis disorders and male infertility. And Y chromosome genes are also involved in the occurrence of reproductive system cancers and can increase the susceptibility of other tumors. In addition, the Y chromosome has very special value in the personal identification and parentage testing of male-related cases in forensic medicine because of its unique paternal genetic characteristics. In view of the extremely high frequency and complexity of gene rearrangements and the limitations of sequencing technology, the analysis of Y chromosome sequences and the study of Y-gene function still have many unsolved problems. This article will introduce the structure and repetitive sequence of the Y chromosome, summarize the correlation between Y chromosome various sequence deletions and male infertility for understanding the repetitive sequence of Y chromosome more systematically, in order to provide research motivation for further explore of the molecules mechanism of Y-deletion and male infertility and theoretical foundations for the transformation of basic research into applications in clinical medicine and forensic medicine.

Copy number variation of ZNF280BY across eight sheep breeds and its association with testicular size of Hu sheep

ZNF280BY, a bovid-specific Y chromosome gene, was firstly found to be highly expressed in bovine testis, indicating it may play important roles in testicular development and male fertility. In this study, we firstly cloned the full-length cDNA of ovine ZNF280BY containing 1993 bp, and with a 1632 bp open reading frame. ZNF280BY was predominantly expressed in the testis, and its expression level was significantly higher in large testis than in small testis in Hu sheep at 6 months of age. In addition, the expression level of ZNF280BY significantly increased during testicular development, showing the highest expression level at 12 months of age. ZNF280BY showed copy number variation (CNV) in 723 rams from eight sheep breeds, ranging from 17 to 514 copies, with a median copy number of 188. Pearson correlation analysis showed that the CNV of ZNF280BY was negatively correlated with testis size in Hu sheep. Furthermore, its mRNA expression level in testis had no significant correlation with the CNV but was significantly correlated with testis size. This study concluded that the expression of ZNF280BY was closely related to testicular development, and the CNV of ZNF280BY could be used as an important genetic marker to evaluate the ram reproductive capacity at an early stage in Hu sheep.

Favoring Expression of Yak Alleles in Interspecies F1 Hybrids of Cattle and Yak Under High-Altitude Environments

Both cis- and trans-regulation could cause differential expression between the parental alleles in diploid species that might have broad biological implications. Due to the relatively distant genetic divergence between cattle and yak, as well as their differential adaptation to high-altitude environments, we investigated genome-wide allelic differential expression (ADE) in their F1 hybrids using Nanopore long-read RNA-seq technology. From adult F1 hybrids raised in high-altitude, ten lung and liver tissues were individually sequenced for producing 31.6 M full-length transcript sequences. Mapping against autosomal homologous regions between cattle and yak, we detected 17,744 and 14,542 protein-encoding genes expressed in lung and liver tissues, respectively. According to the parental assignments of transcript sequences, a total of 3,381 genes were detected to show ADE in at least one sample. There were 186 genes showing ubiquitous ADE in all the studied animals, and among them 135 and 37 genes had consistent higher expression of yak and cattle alleles, respectively. Functional analyses revealed that the genes with favoring expression of yak alleles have been involved in the biological progresses related with hypoxia adaptation and immune response. In contrast, the genes with favoring expression of cattle alleles have been enriched into different biological progresses, such as secretion of endocrine hormones and lipid metabolism. Our results would support unequal contribution of parental genes to environmental adaptation in the F1 hybrids of cattle and yak.

Effects of demethylase KDM4B on the biological characteristics and function of yak cumulus cells in vitro

The present study aims to investigate the expression and function of lysine-specific demethylase 4B (KDM4B) in yak cumulus cells (CCs) in order to reveal the mechanisms by which KDM4B regulates biological characteristics and function of CCs. The cellular location of KDM4B and the methylation pattern of H3K9 were detected using immunofluorescence (IF) staining in CCs. The mRNA expression levels of apoptosis-related genes (BCL-2, HAX1 and BAX) and genes related to the estrogen pathway (ESR2, CYP17 and 3B-HSD) were estimated by qRT-PCR after knockdown of KDM4B expression by siRNA in yak CCs. Then, a proliferation assay, Annexin V-FITC staining, and ELISA were utilized to explore the effects of KDM4B silencing on CCs proliferation, apoptosis, and estrogen (E₂) secretion, respectively. The results showed that KDM4B is located in the nuclei of yak CCs and is distributed in a dotted pattern. Knockdown KDM4B induced a decrease in cell proliferation, an increase in apoptotic rate and a reduction in the levels of E₂ secretion of CCs. Additionally, the methylation patterns of H3K9me2 and H3K9me3 were significantly increased in CCs transfected with KDM4B siRNA-1 (P < 0.05). The mRNA expression level of apoptosis promoting BAX genes was significantly upregulated, but 3B-HSD, ESR2 and anti-apoptotic HAX1 genes were significantly downregulated in transfected CCs (P < 0.05). Furthermore, the rate of embryos developing from the 2-cell stage to blastocysts was lower in the siRNA-1 transfection group than that of the control group (28.6 ± 2.9% vs 40.4 ± 2.4%, P < 0.05). In conclusion, our study indicates that KDM4B regulates the biological characteristics and physiological function of yak CCs mainly through changing the methylation patterns of H3K9 and related gene expression levels.

The assembly of caprine Y chromosome sequence reveals a unique paternal phylogenetic pattern and improves our understanding of the origin of domestic goat

The mammalian Y chromosome offers a unique perspective on the male reproduction and paternal evolutionary histories. However, further understanding of the Y chromosome biology for most mammals is hindered by the lack of a Y chromosome assembly. This study presents an integrated in silico strategy for identifying and assembling the goat Y-linked scaffolds using existing data. A total of 11.5 Mb Y-linked sequences were clustered into 33 scaffolds, and 187 protein-coding genes were annotated. We also identified high abundance of repetitive elements. A 5.84 Mb subset was further ordered into an assembly with the evidence from the goat radiation hybrid map (RH map). The existing whole-genome resequencing data of 96 goats (worldwide distribution) were utilized to exploit the paternal relationships among bezoars and domestic goats. Goat paternal lineages were clearly divided into two clades (Y1 and Y2), predating the goat domestication. Demographic history analyses indicated that maternal lineages experienced a bottleneck effect around 2,000 YBP (years before present), after which goats belonging to the A haplogroup spread worldwide from the Near East. As opposed to this, paternal lineages experienced a population decline around the 10,000 YBP. The evidence from the Y chromosome suggests that male goats were not affected by the A haplogroup worldwide transmission, which implies sexually unbalanced contribution to the goat trade and population expansion in post-Neolithic period.

Molecular characterization of the Yp11.2 region deletion in the Chinese Han population

The Y chromosome is male-specific and is important for spermatogenesis and male fertility. However, the Y chromosome is poorly characterized due to massive palindromes and inverted repeats, which increase the likelihood of genomic rearrangements, resulting in short tandem repeats on the Y chromosome or long fragment deletions. The present study reports a large-scale (2.573~2.648 Mb) deletion in the Yp11.2 region in a Chinese population based on the analysis of 34 selected Y-specific sequence-tagged sites and subsequent sequencing of the breakpoint junctions on the Y chromosome from 5,068,482–5,142,391 bp to 7,715,462–7,716,695 bp. The results of sequence analysis indicated that the deleted region included part or all of the following five genes: PCDH11Y, TSPY, AMELY, TBL1Y, and RKY. These genes are associated with spermatogenesis or amelogenesis and various other processes; however, specific physiological functions and molecular mechanisms of these genes remain unclear. Notably, individuals with this deletion pattern did not have an obvious pathological phenotype but manifested some degree of amelogenesis imperfecta.

Male hybrid sterility in the cattle-yak and other bovines: a review

Hybridization is important for both animal breeders attempting to fix new phenotypic traits and researchers trying to unravel the mechanism of reproductive barriers in hybrid species and the process of speciation. In interspecies animal hybrids, gains made in terms of adaptation to environmental conditions and hybrid vigor may be offset by reduced fertility or sterility. Bovine hybrids exhibit remarkable hybrid vigor compared to their parents. However, the F1 male hybrid exhibits sterility, whereas the female is fertile. This male-biased sterility is consistent with the Haldane rule where heterogametic sex is preferentially rare, absent, or sterile in the progeny of two different species. The obstacle of fixing favorable traits and passing them to subsequent generations due to the male sterility is a major setback in improving the reproductive potential of bovines through hybridization. Multiperspective approaches such as molecular genetics, proteomics, transcriptomics, physiology, and endocrinology have been used by several researchers over the past decade in an attempt to unravel the potential mechanisms underlying male hybrid sterility. However, the mechanism of sterility in the hybrid male is still not completely unravelled. This review seeks to provide an update of the mechanisms of the sterility in the cattle-yak and other bovines.

Inheritance patterns of leukocyte gene expression under heat stress in F1 hybrid cattle and their parents

Crossbreeding capitalizes on heterosis effects and results in increased performance of crossbred animals. Dominance hypothesis and overdominance hypothesis are 2 common models proposed to explain heterosis. Differential gene expression between parents and hybrids is hypothesized to be responsible for heterosis. This study aimed to investigate the heat tolerance and inheritance patterns of leukocyte transcriptomics in F₁ hybrid cattle (Angus males × Droughtmaster females) and their parents Red Angus (AN) and Droughtmaster (DR) under heat stress. According to the respiratory rate and heat tolerance coefficient index, DR was better adapted to heat stress than AN. The physiological responses to heat stress of F₁ hybrids were similar to AN. We identified 802 differentially expressed genes in leukocytes between AN and DR under heat stress using mRNA sequencing. Compared with AN, upregulated genes in DR were enriched in biological processes of response to stress, external and chemical stimulus, and cytokine, cell surface receptor signaling pathway, and cardiovascular system development. In contrast, upregulated genes in AN were enriched in B cell activation and regulation of B cell activation. Gene expression levels can be inherited additively or nonadditively and are classified into additive (35%), dominance (44%), and overdominance and underdominance (18%) modes in F₁ hybrids and their parents. Inheritance patterns of gene expression showed that 97% (249/255) of the dominant genes were classified as paternal AN dominant in hybrids. The paternal imprinted PEG10 gene and its regulatory transcription factor MYC showed an AN dominant expression pattern. The MYC interacted with most AN dominant genes. These transcriptomic analyses revealed that DR and AN had specific cellular and humoral immunity and cardiovascular systems development function under heat stress. Inheritance pattern analyses from gene expression partly explained phenotypic differences between parents and F₁ hybrids. The paternal imprinted PEG10 gene interaction with transcription factor MYC may contribute to explaining paternal dominant gene expression in hybrids.

Cloning and Expression Analysis of Two Kdm Lysine Demethylases in the Testes of Mature Yaks and Their Sterile Hybrids

Simple Summary

The hybrid of male cattle (Bos taurus) with female yaks (Bos grunniens) is called the cattle–yak. All female cattle–yaks are fertile, but all males are sterile. To date, there is no clear conclusion on the mechanism leading to cattle–yak male sterility. The domain conservation and expression profiles of lysine histone demethylases (KDMs) suggest that they might play important roles during gametogenesis. The objective of this study was to explore the molecular mechanism for male sterility of yak hybrids based on two demethylases, KDM1A and KDM4B. The mRNA and protein expression of KDM1A and KDM4B were dramatically decreased in the testes of adult cattle–yaks compared with adult yaks. In addition, the level of H3K36me3 in the testes of cattle–yaks was significantly lower than in yaks. These results suggest that the male sterility of cattle–yaks might be associated with reduced histone methylation modifications. These results provide valuable epigenetic information regarding the molecular mechanism resulting in male sterility of cattle–yaks.

Abstract

The objective of this study was to explore the molecular mechanism for male sterility of yak hybrids based on two demethylases. Total RNA was extracted from the testes of adult yaks (n = 10) and yak hybrids (cattle–yaks, n = 10). The coding sequences (CDS) of two lysine demethylases (KDMs), KDM1A and KDM4B, were cloned by RT-PCR. The levels of KDM1A and KDM4B in yaks and cattle–yaks testes were detected using Real-time PCR and Western blotting for mRNA and protein, respectively. In addition, the histone methylation modifications of H3K36me3 and H3K27me3 were compared between testes of yaks and cattle–yaks using ELISA. The CDS of KDM1A and KDM4B were obtained from yak testes. The results showed that the CDS of KDM1A exhibited two variants: variant 1 has a CDS of 2622 bp, encoding 873 amino acids, while variant 2 has a CDS of 2562 bp, encoding 853 amino acids. The CDS of the KDM4B gene was 3351 bp in length, encoding 1116 amino acids. The mRNA and protein expression of KDM1A and KDM4B, as well as the level of H3K36me3, were dramatically decreased in the testes of cattle–yaks compared with yaks. The present results suggest that the male sterility of cattle–yaks might be associated with reduced histone methylation modifications.

Promoter hypermethylation of PIWI/piRNA pathway genes associated with diminished pachytene piRNA production in bovine hybrid male sterility

Hybrid male sterility (HMS) is a postzygotic reproductive isolation mechanism that enforces speciation. A bovine example of HMS is the yattle (also called dzo), an interspecies hybrid of taurine cattle (Bos taurus) and yak (Bos grunniens). The molecular mechanisms underlying HMS of yattle are not well understood. Epigenetic modifications of DNA methylation and P-element induced wimpy testis (PIWI)-interacting RNA (piRNAs) are important regulators in spermatogenesis. In this study, we investigated DNA methylation patterns and piRNA expression in adult testes in hybrid infertile yattle bulls and fertile cattle and yak bulls using whole genome bisulphite-seq and small RNA-seq. Promoter hypermethylation in yattle were associated with DNA methylation involved in gamete generation, piRNA metabolic processes, spermatogenesis, and spermatid development (P < 2.6 × 10^-5). Male infertility in yattle was associated with the promoter hypermethylation-associated silencing of PIWI/piRNA pathway genes including PIWIL1, DDX4, PLD6, MAEL, FKBP6, TDRD1 and TDRD5. The downstream effects of silencing these genes were diminished production of 29- to 31- nucleotide pachytene piRNAs in yattle testes. Hypermethylation events at transposable element loci (LINEs, SINEs, and LTRs) were found in yattle. LINE-derived prepachytene piRNAs increased and SINE-derived prepachytene piRNAs were reduced in yattle testes. Our data suggests that DNA methylation affects the PIWI/piRNA pathway and is involved in gene expression and pachytene piRNA production during spermatogenesis in bovine HMS. DNA hypermethylation and disruption of piRNA production contributed to unsuccessful germ cell development that may drive bovine HMS.

Comparison of mRNA expression from Y-chromosome X-degenerate region genes in taurine cattle, yaks and interspecific hybrid bulls

The yattle (dzo) is an interspecific hybrid of the taurine cattle (Bos taurus) and the domestic yak (Bos grunniens). F₁ hybrid yattle bulls are sterile due to spermatogenic arrest and have misregulation of spermatogenesis genes in the testes. However, the expression pattern of Y chromosome-linked genes in cattle, yaks and yattle testes is still unknown. In this study, we analyzed the mRNA expression pattern of 10 genes known to be present as single copies in the X-degenerate region of the bovine male-specific region of the Y chromosome. Using male-specific primers and reverse transcription quantitative PCR, the ubiquitously transcribed tetratricopeptide repeat gene, Y-linked (UTY), oral-facial-digital syndrome 1, Y-linked (OFD1Y) and ubiquitin specific peptidase 9, Y-linked (USP9Y) genes were ubiquitously expressed and significantly more highly expressed in yattle than in cattle and yaks testes (P < 0.001). RNA binding motif protein, Y-linked (RBMY) had testes-specific expression, and eukaryotic translation initiation factor 1A, Y-linked (EIF1AY) was expressed mainly in testis, whereas yattle and cattle did not show significant differences with respect to the expression of RBMY and EIF1AY. Thus, based on the model of yattle bull sterility, the high expression of UTY, OFD1Y and USP9Y may be associated with yattle infertility.