Question: lobulo-alveolar structure in the breast is caused by
Answer: To a lesser extent than estrogen , progesterone contributes to ductal development at this time , as evidenced by the findings that progesterone receptor ( PR ) knockout mice or mice treated with the PR antagonist mifepristone show delayed ( albeit eventually normal , due to estrogen acting on its own ) ductal growth during puberty and by the fact that progesterone has been found to induce ductal growth on its own in the mouse mammary gland mainly via the induction of the expression of amphiregulin , the same growth factor that estrogen primarily induces