Spermatogenesis is a complex process of male germ cells proliferation and 
maturation from diploid spermatogonia, through meiosis, to mature haploid 
spermatozoa. The process involves dynamic interactions between the developing 
germ cells and their supporting Sertoli cells. The gonadal tissue, with 
abundance of highly unsaturated fatty acids, high rates of cell division, and 
variety of testis enzymes results very vulnerable to the overexpression of 
reactive oxygen species (ROS). In order to address this risk, testis has 
developed a sophisticated array of antioxidant systems comprising both enzymes 
and free radical scavengers. This chapter sets out the major pathways of testis 
generation, the metabolism of ROS, and highlights the transcriptional regulation 
by steroid receptors of antioxidant stress enzymes and their functional 
implications. It also deals with of the advantages of the system biology for an 
antioxidant under steroid control, the major selenoprotein expressed by germ 
cells in the testis, the phospholipid hydroperoxide glutathione peroxidase 
(PHGPx/GPx4) having multiple functions and representing the pivotal link between 
selenium, sperm quality, and species preservation.