Pitx2 suppression at meiotic stages associates with seasonal inhibition of testis development in Rattus norvegicus caraco

The bicoid-related transcription factor 2 (Pitx2) plays a crucial role in the development of many organs and tissues by affecting the mitotic cell cycle. Postnatal testis development is related to mitosis and meiosis in multiple cell types, but the role of Pitx2 gene in seasonal inhibition of testicular development remains unknown in rodents. We analyzed PITX2 protein and Pitx2 mRNA expression features using both laboratory and wild male Rattus norvegicus caraco. In postnatal testicle of laboratory colony, we found that PITX2 was expressed in Leydig cells, pachytene spermatocytes, round spermatids, and elongating spermatids rather than spermatogonia and leptotene/zygotene spermatocytes. Pitx2b expression significantly increased along with the occurrence of pachytene spermatocytes and round spermatids, while decreased along with the processes of elongated spermatids. In wild male rats with similar testes weight, a significantly suppressed Pitx2b expression occurred with an active meiotic stage in the inhibited testes in autumn and winter, compared with the normally developing testes in spring and summer. These results indicate that Pitx2b expression suppression plays a crucial role in the seasonal inhibition of testis development.