Jun Arita is Professor in the Department of Physiology at the University of Yamanashi in Japan. He received his PhD in Reproductive Neuroendocrinology from Yokohama City University working with Masazumi Kawakami and worked as a post-doctoral fellow at the University of Texas Southwestern Medical School at Dallas. He has been working on the actions of estrogen on hypothalamic and pituitary functions. His current research focuses on how estrogen regulates the proliferation of the pituitary lactotroph, a typical estrogen-responsive cell. He demonstrated that estrogen not only stimulates but also inhibits lactotroph proliferation depending upon the cell context and proposes that the signaling pathway of the anti-proliferative action of estrogen is a target for therapeutic intervention of estrogen-responsive tumors.