The invertebrate ancestry of endocannabinoid signalling: an orthologue of vertebrate cannabinoid receptors in the urochordate Ciona intestinalis
Elphick MR, Satou Y, Satoh N.
School of Biological Sciences, Queen Mary,
University of London, E1 4NS, London, UK
Gene 2003 Jan 2;302(1-2):95-101
ABSTRACTThe G-protein coupled cannabinoid receptors CB(1) and CB(2) are activated by Delta(9)-tetrahydrocannabinol, the psychoactive ingredient of cannabis, and mediate physiological effects of endogenous cannabinoids ('endocannabinoids'). CB(1) genes have been identified in mammals, birds, amphibians and fish, whilst CB(2) genes have been identified in mammals and in the puffer fish Fugu rubripes. Therefore, both CB(1) and CB(2) receptors probably occur throughout the vertebrates. However, cannabinoid receptor genes have yet to be identified in any invertebrate species and the evolutionary origin of cannabinoid receptors is unknown. Here we report the identification of CiCBR, a G-protein coupled receptor in a deuterostomian invertebrate - the urochordate Ciona intestinalis - that is orthologous to vertebrate cannabinoid receptors. The CiCBR cDNA encodes a protein with a predicted length (423 amino-acids) that is the intermediate of human CB(1) (472 amino-acids) and human CB(2) (360-amino-acid) receptors. Interestingly, the protein-coding region of the CiCBR gene is interrupted by seven introns, unlike in vertebrate cannabinoid receptor genes where the protein-coding region is typically intronless. Phylogenetic analysis revealed that CiCBR forms a clade with vertebrate cannabinoid receptors but is positioned outside the CB(1) and CB(2) clades of a phylogenetic tree, indicating that the common ancestor of CiCBR and vertebrate cannabinoid receptors predates a gene (genome) duplication event that gave rise to CB(1)- and CB(2)-type receptors in vertebrates. Importantly, the discovery of CiCBR and the absence of orthologues of CiCBR in protostomian invertebrates such as Drosophila melanogaster and Caenorhabditis elegans indicate that the ancestor of vertebrate CB(1) and CB(2) cannabinoid receptors originated in a deuterostomian invertebrate.CB1
Stoned as a newt?
The nectar of delight
Cannabis and schizophrenia
Cannabinoid receptor subtypes
Distribution of the cannabis receptors
01 02 03 04 05 06 07 08 09 10 11 12 13 14 15
The Hedonistic Imperative
When Is It Best To Take Crack Cocaine?
The Good Drug Guide
The Responsible Parent's Guide
To Healthy Mood Boosters For All The Family