ABSTRACT
A number of polymorphic tandem repeats in human dopamine D4 receptor (DRD4) have been identified in the exons, including a 12-bp repeat in the first exon and a 48-bp repeat in exon III located in the third cytoplasmic loop. However, to determine whether the tandem repeats is specific to humans or not, we have identified and characterized dopamine receptor D4 (DRD4) Exon III tandem repeats in public available nucleotide sequences from 13 different non mammalian species. We found that the tandem repeat was composed of 21-bp modules in sequences from the Mycobacterium smegmatis str. MC2 155, Salinibacter ruber DSM 13855, Danio rerio, Parus major, Corvus macrorhynchos, and Coturnix japonica. A tandem repeat consisting of 30-bp modules was identified in sequence from Melopsittacus undulates while in the Phalacrocorax capillatus and Numida meleagris we identified tandem repeats composed of 3-bp modules. Tandem repeats could not be identified in sequences from Carassius auratus, Phasianus colchicus and Gallus gallus. To understand the evolutionary history of the Exon I region of DRD4—which in humans contains a polymorphic 12bp tandem duplication, a polymorphic 13bp deletion, and other rare variants—we examined the homologous exon in these different species. There was a low degree of similarity between the sequences of bacterial species and those from members of the piscean and avian and with human sequence. We identified transmembrane domain of DRD4 gene and signature of G-protein coupled receptors in the amino acid sequences. The number of transmembrane segments varied pronouncedly between species from 0 to 7 and signature of G-protein coupled receptors was found only in piscean species and was also identified in one avian species (parus major). These findings suggest that an association between Drd4 gene polymorphisms and animal personality variation predates the divergence of the non mammalian and mammalian lineages. Furthermore, the analysis of Drd4 polymorphisms within and among populations may provide information for elucidating the phylogenetic relationship and such data may also provide a clue toward understanding the relation between the genetic variation and behavioral variation in animals.