Comparative Analysis On Whole-genome DNA Methylation Of Primary Spermatocyte Between Cattleyak And Yak

The cattleyak is the offspring of inter-specific hybrid(cattle×yak),which displays equivalent adaptability to harsh surroundings,such as those of the Qinghai-Tibetan Plateau,and exhibits apparent heterosis(also known as hybrid vigor)such as early maturity and high meat production.However,the F1 male of cattleyak is infertile due to spermatogenetic arrest,which has greatly restricted their heterosis in yak breeding.During spermatogenesis,abnormal DNA methylation will cause the spermatogenic gene expression to be disordered,leading to male sterility.Here we for the first time present the genome-wide,single-cell,and single-base resolution landscape of methylated cytosines in two mammalian primary spermatocyte(PSC)genome,from yak with normal spermatogenesis and hybrid infertile cattleyak.We got following results:To our knowledge,this is the first time that sc-WGBS is applied to investigate epigenetic modifications of germ cells from domestic animals.A comparative investigation reveals that widespread differences are observed in the compositions and patterns of DNA cytosine methylation between the two genomes.Compared to yak,global CG or non-CG DNA methylation level as well as m C(m CG,m CHG,m CHH)sites were increased in sterile cattleyak PSC.Otherwise,we observed a high degree of CG DNA methylation throughout all the chromosomes in cattleyak,whereas CG methylation was almost abolished in some chromosome regions(chromosome 1,2,4,6,10,22,23,X)of yak.It is worth noting that the promoters of a larger number of meiosis-specific genes(e.g.,SYCE1/3,SYCP3,RAD51,RAD51 C,XRCC1/2,MOV10L1,MAEL,PIWIL1/2,DDX4,FKBP6,SPACA1,TEX29,TDRD6/9,PRDM1/15,and PLD6)were found to be hypermethylated in cattleyak PSC but fully hypomethylated in yak.RT-qPCR analysis revealed significant reduction expression of corresponding genes in cattleyak PSC relative to yak.These data suggested that the failure to the accumulation of SC component m RNAs and other transcripts in controlling meiosis in cattleyak PSC may contribute to the abnormality of homologous chromosome pairing,DSB/recombination and meiotic arrest in PSC of cattleyak.In despite of the m RNA expression of four genes involved in spermatogonial differentiation,MEIOSIN,SOHLH2,STRA8 and C-KIT,was observed to be upregulated in response to RA at concentrations as high as 1μM,it’s not sufficient to initiate the meiosis after RA induced is blocked to a large degree in cattleyak spermatogonia.These data indicate that the process of initiating meiosis also has a large defect in the spermatogonia of cattleyak.In conclusion,we have derived precise and previously uncharacterized,specific DNA methylation signatures for primary spermatocyte in cattleyak,providing a rich resource for further study in male fertility in cattleyak.