Morphological identification and distribution of telocytes in testis and epididymis of Small-tailed Han sheep before and after sexual maturation.

Telocytes (TCs) are a novel type of stromal cell found in various organs and tissues of mammals, with potential functions including substance transport, mechanical support, and regulation of the microenvironmental stability. This study aims to investigate the existence and morphological differences of TCs in the testis and epididymis of Small-tailed Han sheep before and after sexual maturation using transmission electron microscopy (TEM), toluidine blue staining, immunohistochemistry, double immunofluorescence, and Western blot analysis, and evaluate their function in reproductive regulation. TEM revealed that the TCs located near the basement membrane and blood vessels in the testis and epididymis of Small-tailed Han sheep in two age groups. After sexual maturation, TCs exhibited telopodes (Tps) that were much longer, curved and pronounced distinctions between dilated segments and thin segments, with an increased number of secretory vesicles compared to before sexual maturation. Toluidine blue staining confirmed the presence of TCs near the basement membrane and blood vessels in the interstitial tissue. Immunohistochemistry and double immunofluorescence demonstrated that the positive expression of CD117, Vimentin, platelet derived growth factor receptor α(PDGFR α), PDGFR α+CD117, and PDGFR α+Vimentin in TCs. Additionally, we analyzed the protein expression levels of these markers to infer the potential functions of TCs. The expression of PDGFR α was significantly lower before sexual than after sexual maturation (p < 0.01). On the contrary, CD117 and Vimentin expression levels in the testis and caput epididymis were significantly higher before sexual maturation (p < 0.01), whereas the opposite trend was observed in the corpus and cauda epididymis. We hypothesize that TCs are involved in the spermatogenesis, structural stability of luminal, and sperm transport and maturation in Small-tailed Han sheep. This study is the first to report the characteristics of TCs in the testis and epididymis of Small-tailed Han sheep before and after sexual maturation. The differences in morphology and biomarkers of TCs indicate their role in Small-tailed Han sheep reproduction and provide insights to research the TCs on the reproduction and breeding of animals.