Identification and functional characterization of developmental-stage-dependent piRNAs in Tibetan sheep testes.

The testis in mammals plays an indispensable role in male fertility, in which the development and function are strictly regulated by a variety of non-coding small RNAs. PIWI-interacting RNAs (piRNAs) are the most abundant non-coding small RNAs in mammalian testes, playing an irreplaceable role in testicular development and spermatogenesis. To characterize the piRNA expression and investigate their potential biological function in developmental Tibetan sheep testes, we carried out RNA sequencing. Our results revealed that the length distribution of the identified piRNAs is mostly 24­26 nt and 29 nt, exhibiting a preference for uracil at their 5' end and significant ping-pong structure. Most piRNAs were differentially expressed in Tibetan sheep testes in a development-age-dependent manner, and the vast majority of them were upregulated in postpubertal and adult testes. Based on the functional annotation of piRNA target genes, they were mainly implicated in the regulation of gene expression, transcription, protein modification and development during testicular development and spermatogenesis.