CLONING AND CHARACTERIZATION OF GOLDFISH ACTIVIN TYPE IIB RECEPTOR

We have cloned a full length cDNA coding for the activin type IIB rece ptor (GactRIIB) from the goldfish ovary. GactRIIB shares 73 and 70% am ino acid identity in the extracellular domain, and 78 and 80% identity in the intracellular domain with the type IIB receptors of the mouse and Xenopus respectively. The intracellular domain of GactRIIB contain s two serine kinase consensus sequences, DFKSRN and GTRRYMAPE, in agre ement with the reports in other vertebrates that serine/threonine phos phorylation is involved in activin signal transduction. The identity o f GactRIIB was confirmed by transient expression in the COS cells foll owed by activin binding. Iodinated human activin A bound to the GactRI IB-transfected cells and the binding could be completely inhibited by unlabeled activin. Affinity labeling revealed a band of about 85 kDa, which is in agreement with the reported type II receptors in other ver tebrates. Together with the fact that activin is expressed in the gold fish ovary, the cloning of activin receptors from the ovary suggests p aracrine and autocrine roles for activin in the goldfish ovarian funct ions.