Genomic Study of Dopamine Receptor Ligand Binding Sites of the Bivalve Crassostrea virginica

Abstract

Gill lateral cells of Crassostrea virginica are innervated by dopamine (DA) and serotonin nerves. DA slows down lateral cell cilia beating rates and serotonin accelerates them. DA receptors are classified as D1R and D2R. Physiology and cell biology work of our lab found the DA receptors involved in gill lateral cell cilia inhibition are D2R‐like in the gill cells and D1R‐like in the cerebral and visceral ganglia. Our HPLC studies found DA in various tissues, including gill, cerebral and visceral ganglia of Crassostrea virginica. Using immunofluorescence techniques, we showed the presence of DA neurons in cerebral and visceral ganglia as well as D2R‐like postsynaptic receptors in gill lateral cells and D1R‐like postsynaptic receptors in cerebral and visceral ganglia. Recently the genomes of C. virginica and other bivalves have begun to be mapped. By conducting searches of the NCBI (National Center for Biotechnology Information) database using DNA and protein sequences of C. virginica and other invertebrate and mammalian species we found matches for D1R genes on chromosomes 4 and 5, and D2R genes on chromosomes 3 and 5 of C. virginica. BLASTS of the receptors found matches with very low Expect Values (E values) and high Percent Identity of the D1R and D2R receptors to those in other bivalves, gastropods, insects, mice, rats and humans. Various invertebrates had Percent Identity above 60%, while humans and mice had Percent Identity of 30 ‐ 40%. We hypothesize that the ligand binding sites (LBS) for D1R and D2R receptors in C. virginica are evolutionarily conserved and will closely match those of other animals. To study this, we searched the NCBI database for D1R and D2R LBS of C. virginica and compared them to other animals. We found D2R LBS contained 17 amino acids (W, D, V, S, F, T, L, S, S, S, W, F, F, N, F, T, Y) with very highly conserved (70 ‐ 100%) to LBS of other bivalves, gastropods, insects, mice, rats and humans. D1R LBS have not yet been identified in C. virginica, nor in the other animals we searched for, except for humans where it contained 17 amino acids (W, D, I, S, T, S, A, S, S, S, W, F, F, N, F, V, W). The study complements our physiology and cell biology studies demonstrating the presence and function for DA in C. virginica, and shows the genome of C. virginica contains genes to produce DA receptor LBS that are similar to those of other animals. This new information is valuable as it shows that the simple nervous system of C. virginica can be used to expand studies on DA neurotransmission.