Molecular mechanism of estrogen action in the male: insights from the estrogen receptor null mice

Until recently, 17 beta -estradiol was thought to be of little importance i n male fertility. However, the descriptions of testicular dysfunction and b ehavioral deficits leading to complete infertility in male mice lacking est rogen receptor alpha (ER alpha) have indicated the importance of estrogen a ction in fertility of the male rodent. In contrast, male mice lacking the n ewly discovered estrogen receptor beta (ER beta) exhibit no compromised fer tility. Recently, elaborate sperm transplantation studies have shown that t he altered sperm function characteristic of the ER alpha knockout male are the result of the loss of ER alpha actions in the supporting somatic cells of the testis and epididymis rather than in the germ cell. This brief revie w will discuss the roles of estrogen action in male reproduction as reveale d by mice lacking both known forms of the ER. A brief review of the estroge n signaling system is also included.