Molecular and Cellular Endocrinology 153 (1999) 169 – 181 Cloning of zebrafish activin type IIB receptor (ActRIIB) cDNA and mRNA expression of ActRIIB in embryos and adult tissues R.R. Garg a , L. Bally-Cuif b , S.E. Lee c , Z. Gong c , X. Ni a , C.L. Hew d , C. Peng a, * a Department of Biology, York Uniersity, 4700 Keele St., North York, Toronto, ON M3J 1P3, Canada b Department of Molecular Biology, Princeton Uniersity, Princeton, USA and CNRS URA 1414 E ´ quipe Re ´gionalisation Nereuse, E ´ cole Normale Supe ´rieure, Paris, France and GSF Forschungszentrum, Institet fuer Saeugetiergenetik, Ingolstaedter Landstradde 1, Neuherberg, Germany c School of Biological Sciences, National Uniersity of Singapore, Singapore d Department of Laboratory Medicine and Pathobiology, Uniersity of Toronto, Toronto, Canada Received 11 December 1998; accepted 18 February 1999 Abstract A full-length cDNA encoding for activin type IIB receptor (ActRIIB) was cloned from zebrafish embryos. It encodes a protein with 509 amino acids consisting of a signal peptide, an extracellular ligand binding domain, a single transmembrane region, and an intracellular kinase domain with predicted serine/threonine specificity. The extracellular domain shows 74 – 91% sequence identity to human, bovine, mouse, rat, chicken, Xenopus and goldfish activin type IIB receptors, while the transmembrane region and the kinase domain show 67–78% and 82–88% identity to these known activin IIB receptors, respectively. In adult zebrafish, ActRIIB mRNA was detected by RT-PCR in the gonads, as well as in non-reproductive tissues, including the brain, heart and muscle. In situ hybridization on ovarian sections further localized ActRIIB mRNA to cytoplasm of oocytes at different stages of development. Using whole-mount in situ hybridization, ActRIIB mRNA was found to be expressed at all stages of embryogenesis examined, including the sphere, shield, tail bud, and 6-7 somite. These results provide the first evidence that ActRIIB mRNA is widely distributed in fish embryonic and adult tissues. Cloning of zebrafish ActRIIB demonstrates that this receptor is highly conserved during vertebrate evolution and provides a basis for further studies on the role of activin in reproduction and development in lower vertebrates. © 1999 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Activin IIB receptor; Cloning; mRNA expression; Ovary; Embryos; Zebrafish 1. Introduction Activin is a growth and differentiation factor belong- ing to the transforming growth factor  (TGF) family (reviewed by Mathews, 1994). Activin exists in at least three isoforms, activin A, activin B and activin AB, which result from dimerization of two independent gene products: A and/or B subunits (Mathews, 1994). Although activin was originally isolated from porcine follicular fluid based on its ability to stimulate pituitary follicle-stimulating hormone secretion, it is now clear that it functions as an autocrine/paracrine regulator in a variety of tissues (Mathews, 1994). There is increasing evidence which indicates that activin is involved in many physiological processes, particularly in reproduc- tion and development. Activin has been shown to regu- late: (1) gonadal hormone production and gametogenesis (Hutchinson et al., 1987; Itoh et al., 1990; Mather et al., 1990; Mauduit et al., 1991; Li et al., 1995; Peng et al., 1996); (2) placental hormone production (Qu and Thomas, 1995; Petraglia et al., 1996); (3) neuronal cell survival (Schubert et al., 1990); (4) proliferation of a variety of cell types (Kojima and Ogata, 1989; McCarthy and Bicknell, 1993); (5) ery- thropoiesis (Eto et al., 1987); and (6) induction of mesoderm formation during early embryonic develop- * Corresponding author. Tel.: +1-416-7362100, ext. 40558; fax: +1-416-7365698. E-mail address: cpeng@turing.sci.yorku.ca (C. Peng) 0303-7207/99/$ - see front matter © 1999 Elsevier Science Ireland Ltd. All rights reserved. PII:S0303-7207(99)00044-1