Identification and characterization of a tandem repeat in exon III of the dopamine receptor D4 (DRD4) gene in cetaceans.
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.
Research Institute of Biological Psychiatry, H:S Sct. Hans Hospital, Copenhagen University, 2 Boserupvej, DK-4000 Roskilde, Denmark.
Line
L
Mogensen
Carl Christian
CC
Kinze
Thomas
T
Werge
Henrik Berg
HB
Rasmussen
D000818:Animals; D001483:Base Sequence; D002591:Cetacea / Q000235:genetics*; D017931:DNA Primers; D005091:Exons; D050638:Receptors, Dopamine D4 / Q000235:genetics*; D020080:Tandem Repeat Sequences
D017931:DNA Primers; D050638:Receptors, Dopamine D4