JAK-STAT pathway: Testicular development, spermatogenesis and fertility

Since its discovery in the early 1990s, the JAK-STAT pathway has been deeply explored to unfold the biological responses mediated by this pathway. Originally identified as the signal transduction pathway of interferons, it is now known to be activated by numerous ligands such as cytokines, growth factors and hormones. It has been studied in a wide range of organisms from flies to mammals. In mammals, JAK-STAT is known to regulate various functions such as energy homeostasis, cell proliferation, development and apoptosis, while in Drosophila, it is known to regulate embryonic development, segmentation, spermatogenesis and oogenesis. Mammals have got a number of JAK and STAT homologues and diversity of ligands as compared to Drosophila, which has a single copy of the receptor, JAK, and STAT molecules. The major events of male reproduction, i.e., germline sexual development, germline stem cell maintenance and sperm functions, such as capacitation and motility, are regulated by JAK-STAT signaling. This chapter focuses on the functions of the JAK-STAT pathway in male gonads from sexual development to sperm maturation.