ALK-6

ALK-6, also known as CDw293 (cluster of differentiation w293), is a member of the bone morphogenetic protein (BMP) receptor family of transmembrane serine/threonine kinases. BMPs are involved in endochondral bone formation and embryogenesis, transducing signals through the formation of heteromeric complexes of 2 types BMP receptors: type I receptors (50-55 kD) and type II receptors (70-80 kD). Type II receptors phosphorylate and activate type I receptors which autophosphorylate, then bind and activate SMAD transcriptional regulators^[1]. ALK-6 is the receptor for BMP-7/OP-1 and GDF-5, positively regulates chondrocyte differentiation through GDF-5 interaction^[2]. ALK-6 signaling is also controlled by SCUBE3, a BMP-2/BMP-4 co-receptor, recruits the BMP receptor complexes into raft microdomains, and positively modulates signaling possibly by augmenting the specific interactions between BMPs and BMP type I receptors^[3]. ALK-6 involves in controlling growth, morphogenesis, and bone and teeth development through modulation of BMP signaling, is essential for chondrogenesis in vivo, while BMPR1A/ALK-3 and ALK-6 have overlapping functions during early chondrogenesis^[4]. ALK-6/GDF-9/BMP-15 signals play a key role in prolificacy. ALK-6 and GDF-9 are widely expressed in 20 tissues with highest in ovary, while BMP-15 gene was expressed exclusively in ovary and pituitary^[5]. The sequences of ALK-6 are highly conserved among different species, and the sequence of human shares a high similarity with rat (98.21%) and mouse (98.21%), respectively.

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