The fifth neurohypophysial hormone receptor is structurally related to the V2-type receptor but functionally similar to V1-type receptors Yoko Yamaguchi a,⇑ , Hiroyuki Kaiya b , Norifumi Konno c , Eri Iwata d , Mikiya Miyazato b , Minoru Uchiyama c , Justin D. Bell e , Tes Toop e , John A. Donald e , Sydney Brenner f , Byrappa Venkatesh f , Susumu Hyodo a a Laboratory of Physiology, Atmosphere and Ocean Research Institute, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8564, Japan b Department of Biochemistry, National Cerebral and Cardiovascular Center Research Institute, 5-7-1 Fujishirodai, Suita, Osaka 565-8565, Japan c Department of Biological Science, Graduate School of Science and Engineering, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan d College of Science and Engineering, Iwaki Meisei University, 5-5-1 Chuoudai, Ihino, Iwaki, Fukushima 970-8551, Japan e School of Life and Environmental Sciences, Deakin University, Pigdons Road, Waurn Ponds, Victoria 3216, Australia f Comparative Genomics Laboratory, Institute of Molecular and Cell Biology, A / STAR (Agency for Science, Technology and Research), Biopolis, Singapore 138673, Singapore article info Article history: Received 1 January 2012 Revised 29 June 2012 Accepted 8 July 2012 Available online 16 July 2012 Keywords: Neurohypophysial hormone Vasotocin G protein-coupled receptor Cartilaginous fish Molecular evolution abstract The neurohypophysial peptides of the vasopressin (VP) and oxytocin (OT) families regulate salt and water homeostasis and reproduction through distinct G protein-coupled receptors. The current thinking is that there are four neurohypophysial hormone receptors (V1aR, V1bR, V2R, and OTR) in vertebrates, and their evolutionary history is still debated. We report the identification of a fifth neurohypophysial hormone receptor (V2bR) from the holocephalan elephant fish. This receptor is similar to conventional V2R (V2aR) in sequence, but induced Ca 2+ signaling in response to vasotocin (VT), the non-mammalian VP ortholog; such signaling is typical of V1-type receptors. In addition, V1aR, V1bR and OTR were also isolated from the elephant fish. Further screening revealed that orthologous V2bRs are widely distributed through- out the jawed vertebrates, and that the V2bR family is subdivided into two subfamilies: the fish specific type-1, and a type-2 that is characteristically found in tetrapods. Analysis suggested that the mammalian V2bR may have lost its function. Based on molecular phylogenetic, synteny and functional analyses, we propose a new evolutionary history for the neurohypophysial hormone receptors in vertebrates as follows: the first duplication generated V1aR/V1bR/OTR and V2aR/V2bR lineages; after divergence from the V2bR lineage, the V2aRs evolved to use cAMP as a second messenger, while the V2bRs retained the original Ca 2+ signaling system. Future studies on the role of V2bR in the brain, heart, kidney and reproductive organs, in which it is highly expressed, will open a new research field in VP/VT physiology and evolution. Ó 2012 Elsevier Inc. All rights reserved. 1. Introduction Neurohypophysial hormones are nonapeptides that predomi- nantly regulate water and salt homeostasis and reproduction. Since the pioneering work of du Vigneaud and co-workers [27,33], much research has led to the identification of neurohypophysial hor- mones and their receptors [1,3,6]. It is known that the neurohypo- physial hormones exist in all vertebrate species [4], and the related peptides can also be found from various invertebrates, such as Urochordata [16], Mollusca [24], Annelida [26] and Arthropoda [30]. Neurohypophysial hormones are thus one of the most widely distributed hormone systems in the animal kingdom. In vertebrates, the neurohypophysial hormone family is com- prised of two subfamilies called the vasopressin (VP)- and oxytocin (OT)-families. While all jawed vertebrates (gnathostomes) have both VP- and OT-family peptides, cyclostomes (agnathans) have only a VP-family peptide, vasotocin (VT) [31]. Therefore, it has been believed that the OT-family peptide emerged from an ancestral VT by gene duplication during evolution from agnathans to gnathosto- mes. In gnathostomes, the sequences of the mature peptides and mRNAs have been determined in a large number of species, and their molecular evolution has been well-documented [1,34]. Neurohypophysial hormones are known to signal through their specific G protein-coupled receptors [3,6], but unlike the peptides, research on neurohypophysial hormone receptors has received less attention. In mammals, three VP receptors (V1aR, V1bR, and V2R) 0016-6480/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.ygcen.2012.07.008 ⇑ Corresponding author. Fax: +81 4 7136 6206. E-mail addresses: proton@aori.u-tokyo.ac.jp (Y. Yamaguchi), kaiya@ri.ncvc.go.jp (H. Kaiya), nkonno@sci.u-toyama.ac.jp (N. Konno), asealion@iwakimu.ac.jp (E. Iwata), miyazato@ri.ncvc.go.jp (M. Miyazato), uchiyama@sci.u-toyama.ac.jp (M. Uchiyama), bbeellyy@gmail.com (J.D. Bell), tes.toop@deakin.edu.au (T. Toop), john.donald@deakin.edu.au (J.A. Donald), sydney.brenner@hotmail.com (S. Brenner), mcbbv@imcb.a-star.edu.sg (B. Venkatesh), hyodo@aori.u-tokyo.ac.jp (S. Hyodo). General and Comparative Endocrinology 178 (2012) 519–528 Contents lists available at SciVerse ScienceDirect General and Comparative Endocrinology journal homepage: www.elsevier.com/locate/ygcen