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

Abstract

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.

The relationship between DRD4 polymorphisms and phenotypic correlations of behaviors in the collared flycatcher

“…The gene product is an important component of the dopaminergic system, and its function is linked to many neurological and psychiatric disorders but also contributes to the guidance of normal behaviors such as novelty seeking in humans, although some evidence is at conflict with this general suggestion (Kluger et al 2002;Schinka et al 2002;Reif and Lesch 2003;Ebstein 2006). Moreover, recent studies in other model species, such as different mammals and birds, revealed that polymorphism in the DRD4 gene is associated with novelty seeking, exploration, and escape behavior (Momozawa et al 2005;Mogensen et al 2006;Bailey et al 2007;Fidler et al 2007;Hejjas et al 2007;Gutierrez-Gil et al 2008;Kluen et al 2012). Passerine birds appear particularly important targets for such research, as high degree of mutation rate and codon bias indicates that this genomic region is under strong selection (Abe et al 2011).…”

Drd4 gene polymorphisms are associated with personality variation in a passerine bird

“…Different breeds of domesticated animals (chickens (Gallus gallus), Sugiyama et al 2004; dogs (Canis familiaris), Ito et al 2004) have been found to have differing frequencies of Drd4 alleles, while studies of both domesticated horses (Equus caballus) and captive monkeys (Cercopithecus aethiops) have reported associations between personality parameters and Drd4 gene polymorphisms (Momozawa et al 2005;Bailey et al 2007). Furthermore, Drd4 gene polymorphisms have been reported for free-living species (Mogensen et al 2006), but studies associating this variation with behaviour are absent.…”

Genetic polymorphism as a background of animal behavior

“…2007a,b). Also, the polymorphism of DRD4 has been reported in cetaceans such as sperm whales ( Physeter macrocephalus ) and minke whales ( Balaenoptera acutorostrata ) (Mogensen et al . 2006).…”

“…Further SNP detection of candidate genes and development of anxiety-related parameters using an isolation test in combination with a questionnaire has been conducted by the same group (Momozawa et al 2007a,b). Also, the polymorphism of DRD4 has been reported in cetaceans such as sperm whales (Physeter macrocephalus) and minke whales (Balaenoptera acutorostrata) (Mogensen et al 2006). It is interesting that no similar genetic variation in DRD4 has been found in rodents such as mice or rats (O'Malley et al 1992).…”