Hormone Signaling in the Testis

A complex milieu of hormones initiates diverse signaling pathways within and between cells of the testis to support the processes of steroidogenesis, spermatogenesis, and ultimately male fertility. In this chapter, we discuss the roles, mechanisms, and impacts of hormone signaling within the testis. We describe the mechanisms by which luteinizing hormone promotes the production of testosterone, a hormone essential for spermatogenesis. We use information obtained from cell-specific knockout studies of the androgen receptor as well as cellular and gene expression studies to describe the multifaceted actions of testosterone within the testis. We examine the multiple signaling pathways regulated by follicle-stimulating hormone in Sertoli cells and discuss how these pathways interface with testosterone signaling. In addition, we review how thyroid hormone regulates the proliferation of Sertoli cells and thus determines the capacity for sperm production. Furthermore, the paracrine functions of testis-derived hormones, including estrogen as well as activin and inhibin, are discussed. Finally, the contributions of other hormones that act to fine-tune testicular functions in response to environmental inputs are discussed. Together, these combined data paint a vivid picture of a complex, hormone-regulated signaling environment in the testis that acts to ensure that correct testicular function is maintained throughout life.