Spermatogenesis is mediated by a series of cellular transitions that required tight control of transcription. Snail transcription factors are well known for inducing epithelial-mesenchymal transitions (EMTs) during embryonic development and tumour progression, acting predominantly as transcriptional repressors. However, expression and function of the 3 distinct mammalian Snail proteins are unexplored in the testis. A cursory examination of Snai2-deficient mouse testes indicated reduced seminiferous tubule size and infertility, suggesting Snai2 is required for spermatogenesis.
To test the hypothesis that Snail mRNAs and proteins are important for male fertility, this study provides the first comprehensive analysis of all 3 mammalian Snails in mouse testis. In situ hybridisation and ddPCR revealed that Snai1 and Snai2 transcripts are predominantly detected in adults within spermatogonia and spermatocytes while Snai3 is less restricted and observed in both in germ and Sertoli cells. Immunohistochemistry identified Snai1 in nuclei of spermatocytes, round and elongated spermatids between Stages IX-XII of the seminiferous cycle, Snai2 was selectively present in spermatocyte and round spermatid nuclei transitioning from meiosis into spermiogenesis, while Snai3 was detected only in the Sertoli cell cytoplasm. These data demonstrate that each Snail family member is differentially regulated and indicate each serves unique functions in the adult testis. Subcellular localisation of Snai1 proteins is also distinct and dynamic in juvenile testes. Most intriguing is the presence of Snai1 in the gonocyte cytoplasm at birth, with the signal predominantly nuclear by 5 dpp. Our ongoing work is using cell line, primary and cell line cultures, and mouse models to understand how these key transcriptional regulators contribute to male fertility.