Steroid Receptor Coactivator 2 Is Critical for Progesterone-Dependent Uterine Function and Mammary Morphogenesis in the Mouse

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Abstract
Although the essential involvement of the progesterone receptor (PR) in female reproductive tissues is firmly established, the coregulators preferentially enlisted by PR to mediate its physiological effects have yet to be fully delineated. To further dissect the roles of members of the steroid receptor coactivator (SRC)/p160 family in PR-mediated reproductive processes in vivo, state-of-the-art cre-loxP engineering strategies were employed to generate a mouse model (PRCre/+ SRC-2flox/flox) in which SRC-2 function was abrogated only in cell lineages that express the PR. Fertility tests revealed that while ovarian activity was normal, PRCre/+ SRC-2flox/flox mouse uterine function was severely compromised. Absence of SRC-2 in PR-positive uterine cells was shown to contribute to an early block in embryo implantation, a phenotype not shared by SRC-1 or -3 knockout mice. In addition, histological and molecular analyses revealed an inability of the PRCre/+ SRC-2flox/flox mouse uterus to undergo the necessary cellular and molecular changes that precede complete P-induced decidual progression. Moreover, removal of SRC-1 in the PRCre/+ SRC-2flox/flox mouse uterus resulted in the absence of a decidual response, confirming that uterine SRC-2 and -1 cooperate in P-initiated transcriptional programs which lead to full decidualization. In the case of the mammary gland, whole-mount and histological analysis disclosed the absence of significant ductal side branching and alveologenesis in the hormone-treated PRCre/+ SRC-2flox/flox mammary gland, reinforcing an important role for SRC-2 in cellular proliferative changes that require PR. We conclude that SRC-2 is appropriated by PR in a subset of transcriptional cascades obligate for normal uterine and mammary morphogenesis and function.