C (2009) Androgen receptor roles in spermatogenesis and fertility: lessons from testicular cell-specifi c androgen receptor knockout mice. Endocr Rev 30

Androgens are critical steroid hormones that determine the expression of the male phenotype, including the outward de-velopment of secondary sex characteristics as well as the ini-tiation and maintenance of spermatogenesis. Their actions are mediated by the androgen receptor (AR), a member of the nuclear receptor superfamily. AR functions as a ligand-de-pendent transcription factor, regulating expression of an ar-ray of androgen-responsive genes. Androgen and the AR play important roles in male spermatogenesis and fertility. The recent generation and characterization of male total and con-ditional AR knockout mice from different laboratories dem-onstrated the necessity of AR signaling for both external and internal male phenotype development. As expected, the male total AR knockout mice exhibited female-typical external ap-pearance (including a vagina with a blind end and a clitoris