The Transcriptional Cell Atlas of Testis Development in Sheep at Pre-Sexual Maturity

Sheep testes undergo a dramatic rate of development with structural changes during pre-sexual maturity, including the proliferation and maturation of somatic niche cells and the initiation of spermatogenesis. To explore this complex process, 12,843 testicular cells from three males at pre-sexual maturity (three-month-old) were sequenced using the 10× Genomics Chromium^TM single-cell RNA-seq (scRNA-seq) technology. Nine testicular somatic cell types (Sertoli cells, myoid cells, monocytes, macrophages, Leydig cells, dendritic cells, endothelial cells, smooth muscle cells, and leukocytes) and an unknown cell cluster were observed. In particular, five male germ cell types (including two types of undifferentiated spermatogonia (A_pale and A_dark), primary spermatocytes, secondary spermatocytes, and sperm cells) were identified. Interestingly, A_pale and A_dark were found to be two distinct states of undifferentiated spermatogonia. Further analysis identified specific marker genes, including UCHL1, DDX4, SOHLH1, KITLG, and PCNA, in the germ cells at different states of differentiation. The study revealed significant changes in germline stem cells at pre-sexual maturation, paving the way to explore the candidate factors and pathways for the regulation of germ and somatic cells, and to provide us with opportunities for the establishment of livestock stem cell breeding programs.