BMPR2 and Infertility: Structural studies have shown that ACVR2A and ACVR2B are promiscuous in their binding to various TGFβ superfamily members57,65; therefore, the different phenotypes that we observed in Acvr2a cKO vs. Acvr2b cKO (infertility vs. subfertility) may be the result of tissue-specific abundance of BMP type 2 receptors (i.e., ACVR2A) and its BMP type 1 receptor (i.e., ALK3) during the window of implantation.