The role of follicle-stimulating hormone in spermatogenesis: lessons from knockout animal models.

The development of knockout mouse models for the FSH-beta subunit, the FSH receptor, and LH-receptor performed in different laboratories has confirmed and extended our knowledge concerning the critical role of these hormone-signaling systems in spermatogenesis. In this article, we summarize the phenotypic changes observed in male FSH receptor knockout (FORKO) mice. Young FORKO males have underdeveloped testis with 50% reduction in Sertoli cells, suggesting that FSH-R signaling is required very early for gonadal development, maturity, and function. These mice experience delayed puberty with postponement in the formation of round spermatids. Adult males show reduction in serum testosterone levels despite normal circulating LH concentration, indicating disturbances in Sertoli-Leydig cell communication. As a consequence of reduced sperm production and sperm quality, adult FORKO males have reduced fertility. Aberrant sperm from FORKO males have retention of cytoplasmic droplets and inadequate DNA compaction, hallmarks of infertility in many species including man. Interestingly, these changes are also experimentally inducible in FSH- and/or FSH-R-immunized male bonnet monkeys, creating a state of infertility. Reports of human mutations in FSH-beta and the FSH receptor also indicate that spermatogenesis is dependent on this system. Further investigations in FORKO males should be helpful in uncovering the downstream genes involved in sustaining Sertoli cell function and maintenance of the quantitative and qualitative aspects of spermatogenesis. This might pave the way for treatment of male infertility and contraception.