Gene expression profiling of Activin-like kinase 2 knockout in mice

Implantation of an embryo in the uterus is a multistep process tightly controlled by an intricate regulatory network of interconnected ovarian, uterine, and embryonic factors. Bone morphogenetic protein (BMP) ligands and receptors are expressed in the pregnant uterus, and BMP2 has been shown to be a key regulator of implantation. In this study, we investigated the roles of the BMP type 1 receptor, activin-like kinase 2 (ALK2), during mouse pregnancy by producing uterine-specific Alk2 conditional knockout (cKO) mice. In the absence of ALK2, embryos can invade the uterine epithelium and stroma, but stromal cells cannot undergo uterine decidualization, resulting in sterility. Mechanistically, microarray analysis revealed that CCAAT/enhancer-binding protein (Cebpb) expression is suppressed during decidualization in Alk2 cKO females. These findings and the similar phenotypes of Cebpb cKO and Alk2 cKO mice lead to the hypothesis that BMPs act upstream of C/EBP to regulate decidualization. To test this hypothesis, we knocked down ALK2 in human uterine stromal cells (HESC) and discovered that ablation of ALK2 alters HESC decidualization and suppresses CEBPB mRNA and protein levels. Chromatin immunoprecipitation (ChIP) analysis of decidualizing HESC confirmed that BMP signaling protein, SMAD1, directly regulates expression of CEBPB by binding a distinct regulatory sequence in the CEBPB promoter; C/EBP, in turn, regulates the expression of progesterone receptor (PGR). Our work clarifies the conserved mechanisms through which BMPs regulate embryo implantation in rodents and primates and, for the first time, uncovers a linear pathwayof BMP signaling through ALK2 to regulate CEBPB and, subsequently, PGR during decidualization.

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Clementi C, Tripurani SK, Large MJ, Edson MA, Creighton CJ, Hawkins SM, Kovanci E, Kaartinen V, Lydon JP, Pangas SA, DeMayo FJ, Matzuk MM