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

Genetic parameters and genome-wide association studies including the X chromosome for various reproduction and semen quality traits in Nellore cattle

BACKGROUND

The profitability of the beef industry is directly influenced by the fertility rate and reproductive performance of both males and females, which can be improved through selective breeding. When performing genomic analyses, genetic markers located on the X chromosome have been commonly ignored despite the X chromosome being one of the largest chromosomes in the cattle genome. Therefore, the primary objectives of this study were to: (1) estimate variance components and genetic parameters for eighteen male and five female fertility and reproductive traits in Nellore cattle including X chromosome markers in the analyses; and (2) perform genome-wide association studies and functional genomic analyses to better understand the genetic background of male and female fertility and reproductive performance traits in Nellore cattle.

RESULTS

The percentage of the total direct heritability (h2total) explained by the X chromosome markers (h2x) ranged from 3 to 32% (average: 16.4%) and from 9 to 67% (average: 25.61%) for female reproductive performance and male fertility traits, respectively. Among the traits related to breeding soundness evaluation, the overall bull and semen evaluation and semen quality traits accounted for the highest proportion of h2x relative to h2total with an average of 39.5% and 38.75%, respectively. The total number of significant genomic markers per trait ranged from 7 (seminal vesicle width) to 43 (total major defects). The number of significant markers located on the X chromosome ranged from zero to five. A total of 683, 252, 694, 382, 61, and 77 genes overlapped with the genomic regions identified for traits related to female reproductive performance, semen quality, semen morphology, semen defects, overall bulls' fertility evaluation, and overall semen evaluation traits, respectively. The key candidate genes located on the X chromosome are PRR32, STK26, TMSB4X, TLR7, PRPS2, SMS, SMARCA1, UTP14A, and BCORL1. The main gene ontology terms identified are "Oocyte Meiosis", "Progesterone Mediated Oocyte Maturation", "Thermogenesis", "Sperm Flagellum", and "Innate Immune Response".

CONCLUSIONS

Our findings indicate the key role of genes located on the X chromosome on the phenotypic variability of male and female reproduction and fertility traits in Nellore cattle. Breeding programs aiming to improve these traits should consider adding the information from X chromosome markers in their genomic analyses.

Analysis of genetic evolutionary differences among four Tibetan pig populations in China

Tibetan pigs are a locally bred domestic pig breed originating from the Tibetan Plateau in China. They can be categorized into four distinct groups based on their geographical locations: Sichuan Tibetan pigs, Tibetan pigs from Tibet, Yunnan Tibetan pigs, and Gansu Tibetan pigs. This study aimed to explore population diversity, genetic structure and selection signals among Tibetan pigs in four Chinese national nature reserves. The results show that there is different observed heterozygosity among Tibetan pig populations (0.1957-0.1978). Ratio of runs of homozygosity (Froh) calculation of four Tibetan pig populations by runs of homozygosity (ROH) revealed the presence of inbreeding within the population (0.0336-0.0378). Analysis of the genetic structure demonstrated distinct population stratification among the four Tibetan pig populations, with each showing relatively independent evolutionary directions. Furthermore, Five methods (FST, Piratio, ROD, Tajima's D, XP-CLR) were used to artificially select evolutionary trajectories. The results mainly involved processes such as DNA repair, immune regulation, muscle fat deposition and adaptation to hypoxia. In conclusion, this study enhances our understanding of the genetic characteristics of Tibetan pig populations and provides a theoretical reference for the conservation of resources across different populations of Tibetan pigs.

N6-Methyladenosine Modification-Related Genes Express Differentially in Sterile Male Cattle-Yaks

N6-methyladenosine (m6A), an RNA post-transcriptional modification, plays a crucial role in spermatogenesis. Cattle-yaks are interspecific hybrid offsprings of yak and cattle, and male cattle-yaks are sterile. This study aims to investigate the role of m6A modification in male cattle-yak infertility. Herein, testicular tissues were analyzed via histological observations, immunohistochemical assays, reverse-transcription quantitative polymerase chain reaction, Western blotting, and immunofluorescence assays. The results revealed that male cattle-yaks presented smaller testes (5.933 ± 0.4885 cm vs. 7.150 ± 0.3937 cm), with only single cell layers in seminiferous tubules, and weakened signals of m6A regulators such as METTL14 (methyltransferase-like 14), ALKBH5 (alpha-ketoglutarate-dependent hydroxylase homolog 5), FTO (fat mass and obesity-associated protein), and YTHDF2 (YTH N6-methyladenosine RNA binding protein F2), both at the RNA and protein levels, compared with those of yaks. Altogether, these findings suggest that m6A modification may play a crucial role in male cattle-yak sterility, providing a basis for future studies.

Single-cell analysis identifies critical regulators of spermatogonial development and differentiation in cattle-yak bulls

Spermatogenesis is a continuous process in which functional sperm are produced through a series of mitotic and meiotic divisions and morphological changes in germ cells. The aberrant development and fate transitions of spermatogenic cells cause hybrid sterility in mammals. Cattle-yak, a hybrid animal between taurine cattle (Bos taurus) and yak (Bos grunniens), exhibits male-specific sterility due to spermatogenic failure. In the present study, we performed single-cell RNA sequencing analysis to identify differences in testicular cell composition and the developmental trajectory of spermatogenic cells between yak and cattle-yak. The composition and molecular signatures of spermatogonial subtypes were dramatically different between these 2 animals, and the expression of genes associated with stem cell maintenance, cell differentiation and meiotic entry was altered in cattle-yak, indicating the impairment of undifferentiated spermatogonial fate decisions. Cell communication analysis revealed that signaling within different spermatogenic cell subpopulations was weakened, and progenitor spermatogonia were unable to or delayed receiving and sending signals for transformation to the next stage in cattle-yak. Simultaneously, the communication between niche cells and germ cells was also abnormal. Collectively, we obtained the expression profiles of transcriptome signatures of different germ cells and testicular somatic cell populations at the single-cell level and identified critical regulators of spermatogonial differentiation and meiosis in yak and sterile cattle-yak. The findings of this study shed light on the genetic mechanisms that lead to hybrid sterility and speciation in bovid species.