Molecular evolution and genetic variation of exon 3 inside the dopamine receptor D4 (DRD4) gene sequences among the non-human primates

Abstract

The accessibility of genetic sequences of different genes among the non-human primates, the progressive and advanced knowledge of molecular phylogenetics and the advent of various types of molecular evolutionary genetic analysis softwares have tremendously developed the field of primate evolutionary genetics. Primates bear an extremely enlarged brain and display varieties of behavioural and psychological features for their social interactions with other individuals, so studying a gene like dopamine receptor D4 which has effect on mental activities will be helpful for the interpretation of primate and human evolution. Dopamine is an imperative catecholamine neurotransmitter. Dopamine receptors which are essential membrane proteins, arbitrate the work of dopamine. These receptors perform essential functions inside the brain by way of controlling motor and endocrine functions, expression of emotion, behavioural homeostasis, cognition, memory, sleep, learning, feeding, reward and release of neuroendocrine. These dopamine receptors also accomplish essential functions in cardiovascular function, hormonal regulation, olfaction and renal function among others. The study of the dopamine receptor D4 (DRD4) gene is essential among the other five dopamine receptors because of its extremely polymorphic nature. These polymorphism are expressed through the number of repeat units of the 48-base pairs (bp) sequence coding for 16 amino acids situated inside the 3rd cytoplasmic loop of the dopamine D4 receptor. The dopamine receptor D4 gene repeat unit sequences and its polymorphic expressions have been monitored in several non-human primates and also in humans, signifying that the primary configuration of the dopamine receptor D4 gene has been retained from non-human primate evolution to human evolution. Research on DRD4 gene on non-human primates also have revealed that the number of repeat unit sequences also have enhanced in haplorhines rather than strepsirrhines. It can also be depicted from the research on DRD4 gene among non-human primates that the DRD4 gene found inside humans arose before the branch out of the predecessors of the lineages of New World monkeys from the Old World monkeys and apes.