BMP (Bone Morphogenetic Protein) Receptors are essential, beyond the egg cylinder stage, for myocyte-dependent functions and signals in cardiac organogenesis. ALK3/BMPR1A (Activin Receptor-Like Kinase-3) is specifically required at mid-gestation for norma ...l development of the trabeculae, compact myocardium, interventricular septum and endocardial cushion. The invariable defects in myocardium results from congenital deletion of ALK3 and this provide strong support for its assessment as a candidate gene in human congenital heart disease. BMPs like BMP2, BMP4 and BMP5, BMP7, BMP10, bind to Serine/threonine kinase receptors, Type-I (ALK3/BMPR1A and ALK6/BMPR1B) and Type-II,BMPR2 (Bone Morphogenetic Protein Receptor Type-II),respectively, and form a heteromeric signaling complex acting in series. In the presence of ligand, the Type-II receptor phosphorylates the Type-I receptors, which activate signaling by intracellular effectors including SMAD (Sma and MAD (Mothers Against Decapentaplegic) Related Protein) transcription factors. ALK3 is ubiquitous throughout development, whereas ALK6 is absent from the heart at mid-gestation. ALK3 and BMPR2 are each essential for gastrulation and mesoderm formation. Therefore the existence of human mutations in receptors for BMPs is a cause of clinical cardiovascular disorders including pulmonary hypertension and hereditary hemorrhagic telangiectasia. The loss of ALK3 in mid-gestation myocardium quickly leads to multiple cardiac defects, which coincide with the distribution of BMPs in the heart; BMP2 and BMP4 adjacent to the AV (Atrioventricular) cushion, BMP5 and BMP7 more homogenously and BMP10 in the trabeculae.
View More... View Less...