Members of the TGF pa superfamily signal through the activin/TGFp and/ or BMP pathways (24). The BMP receptors (BMPRIA/ALK3, BMPRIB/ ALK6, and BMPR2) are transmembrane serine/threonine kinases closely related to the transforming growth factor beta receptors (TGFBRI/ ALK5, TGFBR2) and activin receptors (ACVR1, ACVR1B, ACVR2, and ACVR2B). BMP receptors are expressed in granulosa cells and oocytes (25) and the BMPs exert their biological actions by forming heteromeric complexes with type I and II receptors (26). Ligands bind to the type II receptors leading to transphosphorylation of the type I receptor. The type I kinase activates proteins which migrate to the nucleus and together with other proteins regulate expression of target genes. GDF9, BMP15, BMP4, and BMp7 all use BMP2 as a binding receptor (27). BMP15 signals through interaction of BMPR1B and BMPR2 activating the SMAD1/5/8 pathway (28). Consequently, BMP proteins appear to interact with a limited number of receptors to activate two downstream Smad pathways. Moreover, several high-affinity binding proteins including follistatin, noggin, and gremlin antagonize BMP signaling (29). How granulosa cells and other cell types in the ovary differentiate between signals from multiple ligands in this pathway remains unclear.
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A Beginner's Guide to Healthy Pregnancy. If you suspect, or know, that you are pregnant, we ho pe you have already visited your doctor. Presuming that you have confirmed your suspicions and that this is your first child, or that you wish to take better care of yourself d uring pregnancy than you did during your other pregnancies; you have come to the right place.