Histamine is a biogenic amine found in a wide variety of invertebrates . Histamine is particularly well studied in arthropods and gastropods where it is involved in local immune responses as well as regulating physiological functions in the gut. Histamine also functions as a neurotransmitter, especially for sensory systems. Previous physiology work of our lab found that histamine activates the sensory system of Crassostraea virginica , eliciting a motor response in the gill. Our earlier cell biology and immunofluorescence work also showed the presence of histamine receptors in ganglia and mantle of C. virginica . Recently the genome of C. virginica and other bivalves have begun to be mapped. By conducting BLAST 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 histamine receptor H1R genes on chromosome 8; H2R on chromosomes 1, 2, 5 and 10; and H3R on chromosome 3. BLASTS of other invertebrates and mammals found matches with very low Expect Values (E Values) and moderately high Percent Identity, signifying similarities of H1R, H2R and H3R of C. virginica to those of other bivalves, gastropods, insects, mice, rats and humans. We hypothesize that the ligand binding sites (LBS) for H1R, H2R and H3R receptors in C. virginica are evolutionarily conserved and will closely match those of other animals. To study this, we conducted searches of the NCBI database for H1R, H2R and H3R receptors LBS of C. virginica and compared them to other animals. We found the LBS for H2R in C. virginica was identified and match some other invertebrates well, but did not match humans of other mammals very well. The LBS for H3R matched some other bivalves, invertebrates as well as humans and other mammals well. The LBS for H1R in C. virginica and other invertebrates we looked at has not yet been identified. The LBS for H1R in humans and other mammals is very highly conserved. This study complements our earlier physiology and cell biology studies demonstrating the presence and function for histamine in C. virginica , and shows that the genome of C. virginica contains genes to produce histamine receptor LBS that are similar to those of other animals where it has been identified. This new information is valuable as it shows that the simple nervous system of histamine can be used to expand studies on histamine neurotransmission.
This work was supported in part by grant 2R25GM06003 of the Bridge Program of NIGMS, NIH grant K12GM093854-07A1 IRACDA Program of Rutgers University and PSC-CUNY grants 62344-00 50 and 63434-00 51.