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 in male fertility. However, the descriptions of testicular dysfunction and behavioral deficits leading to complete infertility in male mice lacking estrogen receptor alpha (ER alpha) have indicated the importance of estrogen action in fertility of the male rodent. In contrast, male mice lacking the newly discovered estrogen receptor beta (ER beta) exhibit no compromised fertility. Recently, elaborate sperm transplantation studies have shown that the 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 review will discuss the roles of estrogen action in male reproduction as revealed by mice lacking both known forms of the ER. A brief review of the estrogen signaling system is also included.