Localization of CiCBR in the invertebrate chordate Ciona intestinalis: evidence of an ancient role for cannabinoid receptors as axonal regulators of neuronal signalling.
CiCBR is a G-protein-coupled receptor in the sea-squirt Ciona intestinalis and the first ortholog of vertebrate CB(1) and CB(2) cannabinoid receptors to be identified in an invertebrate (Elphick et al. [2003] Gene 302:95-101). Here we have used Western blotting and immunocytochemistry to examine expression of CiCBR in adult Ciona, employing novel antibodies to the C-terminal tail of CiCBR. Consistent with the expected mass for CiCBR, a approximately 47-kDa band was detected in Ciona membranes, and immunocytochemical analysis of serial sections of Ciona revealed intense immunoreactivity in the cerebral ganglion localised in a dense meshwork of fibers in the neuropile. Accordingly, Western blot analysis of neural complex homogenates revealed the presence of a approximately 47-kDa band. CiCBR immunoreactivity was also observed in axons exiting the ganglion in the anterior and posterior nerves, and analysis of whole-mount preparations revealed that these axons project over the interior surface of the oral and atrial siphons. Isolated CiCBR-immunoreactive axons not associated with the anterior and posterior nerves were observed projecting through the cortical layer of the cerebral ganglion. Central and peripheral CiCBR-immunoreactive fibers were studded with intensely stained varicosities, indicative of a role for CiCBR in regulation of axonal release of neurotransmitters, neuromodulators, or neurohormones. Collectively, our data suggest that the well-established role that the CB(1) receptor has as an axonal regulator of neurotransmitter release in mammals may have originated with ancestral-type cannabinoid receptors in invertebrate chordates before the emergence of CB(1)- and CB(2)-type receptors in vertebrates.
Egertová
Michaela
M
School of Biological and Chemical Sciences, Queen Mary, University of London, London E1 4NS, United Kingdom.
Elphick
Maurice R
MR
D000818:Animals; D000918:Antibody Specificity; D001369:Axons / Q000378:metabolism* / Q000648:ultrastructure; D001921:Brain / Q000033:anatomy & histology / Q000378:metabolism; D063385:Cannabinoid Receptor Modulators / Q000378:metabolism*; D043344:Chordata / Q000033:anatomy & histology / Q000378:metabolism; D002938:Ciona intestinalis / Q000033:anatomy & histology / Q000378:metabolism*; D019143:Evolution, Molecular; D017952:Ganglia, Invertebrate / Q000033:anatomy & histology / Q000378:metabolism; D007150:Immunohistochemistry; D009420:Nervous System / Q000033:anatomy & histology / Q000378:metabolism*; D010525:Peripheral Nerves / Q000033:anatomy & histology / Q000378:metabolism; D010802:Phylogeny; D017729:Presynaptic Terminals / Q000378:metabolism / Q000648:ultrastructure; D043882:Receptors, Cannabinoid / Q000378:metabolism*; D013045:Species Specificity; D009435:Synaptic Transmission / Q000502:physiology*
D063385:Cannabinoid Receptor Modulators; D043882:Receptors, Cannabinoid