Gene structure and expression of cg-ALR1, a type I activin-like receptor from the bivalve mollusc Crassostrea gigas.

Members of the transforming growth factor beta superfamily of cell signaling polypeptides have attracted much attention because of their ability, from nematodes to mammals, to control cellular functions that in turn, regulate embryo development and tissue homeostasis (the transforming growth factors betas 95 (1990) 419). To understand the divergent evolution of the structures and functions of the transforming growth factor beta receptors (superfamily) we report here the cloning and characterization of an activin-like type I receptor gene from the oyster Crassostrea gigas (cgALR1). This 6 Kb gene encodes a 534 amino acid long protein consisting of a signal peptide, an extracellular ligand binding domain, a transmembrane region and an intracellular domain. The intracellular domain contains sequence motifs such as the GS box and EIF/V and RIKKTL boxes that are thought to be hallmarks of activin type I receptors. The protein sequence shares 67% amino acid identity with other serine/threonine kinase receptors in the most conserved kinase domain and 47-49% similarity with vertebrate type I receptors. The temporal expression pattern of cgALR1 transcripts was examined during early larval developmental stages. To gain insight into evolutionary diversification, phylogenetic analysis as well as an investigation of the genomic structure, including the promoter region of the cgALR1 gene were carried out.