Journal of Heredity Advance Access originally published online on February 22, 2006
Journal of Heredity 2006 97(3):279-284; doi:10.1093/jhered/esj024
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Brief Communications |
Identification and Characterization of a Tandem Repeat in Exon III of the Dopamine Receptor D4 (DRD4) Gene in Cetaceans
From the Research Institute of Biological Psychiatry, H:S Sct. Hans Hospital, Copenhagen University, 2 Boserupvej, DK-4000 Roskilde, Denmark; and CC Konsult, 35 Falkoner Allé, DK-2000 Frederiksberg, Denmark
Address correspondence to H. B. Rasmussen at the address above, or e-mail: henrik.berg.rasmussen{at}shh.hosp.dk.
A large number of mammalian species harbor a tandem repeat in exon III of the gene encoding dopamine receptor D4 (DRD4), a receptor associated with cognitive functions. In this study, a DRD4 gene exon III tandem repeat from the order Cetacea was identified and characterized. Included in our study were samples from 10 white-beaked dolphins (Lagenorhynchus albirostris), 10 harbor porpoises (Phocoena phocoena), eight sperm whales (Physeter macrocephalus), and five minke whales (Balaenoptera acutorostrata). Using enzymatic amplification followed by sequencing of amplified fragments, a tandem repeat composed of 18-bp basic units was detected in all of these species. The tandem repeats in white-beaked dolphin and harbor porpoise were both monomorphic and consisted of 11 and 12 basic units, respectively. In contrast, the sperm whale harbored a polymorphic tandem repeat with size variants composed of three, four, and five basic units. Also the tandem repeat in minke whale was polymorphic; size variants composed of 6 or 11 basic units were found in this species. The consensus sequences of the basic units were identical in the closely related white-beaked dolphin and harbor porpoise, and these sequences differed by a maximum of two changes when compared to the remaining species. There was a high degree of similarity between the cetacean basic unit consensus sequences and those from members of the horse family and domestic cow, which also harbor a tandem repeat composed of 18-bp basic units in exon III of their DRD4 gene. Consequently, the 18-bp tandem repeat appears to have originated prior to the differentiation of hoofed mammals into odd-toed and even-toed ungulates. The composition of the tandem repeat in cetaceans differed markedly from that in primates, which is composed of 48-bp repeat basic units.
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