Cloning of zebrafish activin type IIB receptor (ActRIIB) cDNA and mRNA expression of ActRIIB in embryos and adult tissues

A full-length cDNA encoding for activin type IIB receptor (ActRIIB) was clo ned from zebrafish embryos. It encodes a protein with 509 amino acids consi sting of a signal peptide, an extracellular ligand binding domain, a single transmembrane region, and an intracellular kinase domain with predicted se rine/threonine specificity. The extracellular domain shows 74-91% sequence identity to human, bovine, mouse, rat, chicken, Xenopus and goldfish activi n type IIB receptors, while the transmembrane region and the kinase domain show 67-78% and 82-88% identity to these known activin IIB receptors, respe ctively. In adult zebrafish, ActRIIB mRNA was detected by RT-PCR in the gon ads, as well as in non-reproductive tissues, including the brain, heart and muscle. In situ hybridization on ovarian sections further localized ActRII B mRNA to cytoplasm of oocytes at different stages of development. Using wh ole-mount in situ hybridization, ActRIIB mRNA was found to be expressed at all stages of embryogenesis examined, including the sphere, shield, tail bu d, and 6-7 somite. These results provide the first evidence that ActRIIB mR NA is widely distributed in fish embryonic and adult tissues. Cloning of ze brafish ActRIIB demonstrates that this receptor is highly conserved during vertebrate evolution and provides a basis for further studies on the role o f activin in reproduction and development in lower vertebrates. (C) 1999 El sevier Science Ireland Ltd. All rights reserved.