Identification and Characterization of a Tandem Repeat in Exon III of the Dopamine Receptor D4 (DRD4) Gene in Cetaceans

• Published in: Journal of Heredity
• Main Authors: Mogensen, Line, Kinze, Carl Christian, Werge, Thomas, Rasmussen, Henrik Berg
• Format: Text
• Language: English
• Published: Oxford University Press 2006
• Subjects: Brief Communications; Balaenoptera acutorostrata; Lagenorhynchus albirostris; minke whale; Phocoena phocoena; Physeter macrocephalus; Sperm whale; White-beaked dolphin
• Online Access: http://jhered.oxfordjournals.org/cgi/content/short/97/3/279; https://doi.org/10.1093/jhered/esj024

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.