BfCBR: A cannabinoid receptor ortholog in the cephalochordate Branchiostoma floridae (Amphioxus) Maurice R. Elphick ⁎ School of Biological and Chemical Sciences, Queen Mary, University of London, London E1 4NS, UK Received 26 March 2007; received in revised form 17 April 2007; accepted 26 April 2007 Received by M. Di Giulio Available online 1 May 2007 Abstract A gene encoding an ortholog of vertebrate CB 1 /CB 2 cannabinoid receptors was recently identified in the urochordate Ciona intestinalis (CiCBR; [Elphick, M.R., Satou, Y., Satoh, N., 2003. The invertebrate ancestry of endocannabinoid signalling: an orthologue of vertebrate cannabinoid receptors in the urochordate Ciona intestinalis. Gene 302, 95–101.]). Here a cannabinoid receptor ortholog (BfCBR) has been identified in the cephalochordate Branchiostoma floridae. BfCBR is encoded by a single exon and is 410 amino acid residue protein that shares 28% sequence identity with CiCBR and 23% sequence identity with human CB 1 and human CB 2 . The discovery of BfCBR and CiCBR and the absence of cannabinoid receptor orthologs in non-chordate invertebrates indicate that CB 1 /CB 2 -like cannabinoid receptors originated in an invertebrate chordate ancestor of urochordates, cephalochordates and vertebrates. Furthermore, analysis of the relationship of BfCBR and CiCBR with vertebrate CB 1 and CB 2 receptors indicates that the gene/genome duplication that gave rise to CB 1 and CB 2 receptors occurred in the vertebrate lineage. Identification of BfCBR, in addition to CiCBR, paves the way for comparative analysis of the expression and functions of these proteins in Branchiostoma and Ciona, respectively, providing an insight into the ancestral functions of cannabinoid receptors in invertebrate chordates prior to the emergence of CB 1 and CB 2 receptors in vertebrates. © 2007 Elsevier B.V. All rights reserved. Keywords: BfCBR; CB 1 ; CB 2 ; CiCBR; Chordate; Deuterostome; Invertebrate 1. Introduction The discovery in the early 1990s of the G-protein coupled cannabinoid receptors CB 1 and CB 2 and the endogenous canna- binoid receptor ligands anandamide and 2-arachidonoylglycerol heralded the emergence of the concept of an “endocannabinoid signalling system” (Piomelli, 2003). Subsequently, anatomical analysis of CB 1 and CB 2 expression, development of selective antagonists and production of CB 1 and CB 2 gene-knockout mice have facilitated elucidation of the physiological roles of this system. Perhaps most significant has been the discovery that pre- synaptic CB 1 receptors mediate retrograde synaptic signalling in the brain by inhibiting release of “classical” neurotransmitters (glutamate, GABA) upon activation by endocannabinoids gen- erated post-synaptically (Elphick and Egertová, 2001; Wilson and Nicoll, 2002; Chevaleyre et al., 2006). At a behavioural level the CB 1 receptor has a variety of functions, including roles in analgesia, extinction of aversive memories and protection of the brain against seizures (Ledent et al., 1999; Zimmer et al., 1999; Marsicano et al., 2002; Monory et al., 2006). The CB 2 receptor is highly expressed in immune cells and analysis of CB 2 -knockout mice indicates that CB 2 is required for macrophage-mediated helper T cell activation (Buckley et al., 2000) and formation of sub-populations of B and T cells (Ziring et al., 2006). The CB 2 receptor is also required for regulation of bone mass (Ofek et al., 2006) and evidence of a regulatory role in neuropathic pain is emerging (Zhang et al., 2003; Beltramo et al., 2006). Although CB 1 and CB 2 share a relatively low level of se- quence identity (44% amino acid identity in humans; Munro et al., 1993), they are more closely related to each other than to any other protein encoded in the human genome and therefore must have evolved from a common ancestral molecule as a Gene 399 (2007) 65 – 71 www.elsevier.com/locate/gene Abbreviations: bp, base pair(s); BLAST, Basic Local Alignment Search Tool; CB 1 , cannabinoid receptor 1; CB 2 , cannabinoid receptor 2; BfCBR, Branchiostoma floridae cannabinoid receptor; CiCBR, Ciona intestinalis cannabinoid receptor; Mb, megabase(s); PCR, polymerase chain reaction. ⁎ Tel.: +44 20 7882 5290; fax: +44 20 8983 0973. E-mail address: M.R.Elphick@qmul.ac.uk. 0378-1119/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.gene.2007.04.025