Germ cell-somatic cell interactions during spermatogenesis.

The adult testis has two essential functions, namely the synthesis and secretion of the steroid hormone testosterone and the production of mature spermatozoa. Germ cells undergo mitosis, meiosis and condensation (spermiation) in close association with Sertoli cells and in defined associations with each other within the seminiferous epithelium. Normal spermatogenesis and fertility are dependent upon paracrine interactions between the somatic cells (Sertoli, Leydig and peritubular) and the germ cells, and upon endocrine support from the pituitary gland. Evidence for paracrine interactions between somatic and germ cells has been gained from observations on the patterns of expression of proteins, studies on isolated cell populations, germ cell or Leydig cell ablation with toxicants, mouse mutants and transgenics, and more recently from germ cell transplantation.