Publication Date:
2013-03-21
Description:
The receptors of the dopamine neurotransmitter belong to two unrelated classes named D 1 and D 2 . For the D 1 receptor class, only two subtypes are found in mammals, the D 1A and D 1B, receptors, whereas additional subtypes, named D 1C , D 1D , and D 1X , have been found in other vertebrate species. Here, we analyzed molecular phylogeny, gene synteny, and gene expression pattern of the D 1 receptor subtypes in a large range of vertebrate species, which leads us to propose a new view of the evolution of D 1 dopamine receptor genes. First, we show that D 1 C and D 1 D receptor sequences are encoded by orthologous genes. Second, the previously identified Cypriniform D 1 X sequence is a teleost-specific paralog of the D 1 B sequences found in all groups of jawed vertebrates. Third, zebrafish and several sauropsid species possess an additional D 1 -like gene, which is likely to form another orthology group of vertebrate ancestral genes, which we propose to name D 1 E . Ancestral jawed vertebrates are thus likely to have possessed four classes of D 1 receptor genes— D 1 A , D 1 B(X) , D 1 C(D) , and D 1 E —which arose from large-scale gene duplications. The D 1 C receptor gene would have been secondarily lost in the mammalian lineage, whereas the D 1 E receptor gene would have been lost independently in several lineages of modern vertebrates. The D 1 A receptors are well conserved throughout jawed vertebrates, whereas sauropsid D 1 C receptors have rapidly diverged, to the point that they were misidentified as D 1 D . The functional significance of the D 1 C receptor loss is not known. It is possible that the function may have been substituted with D 1 A or D 1 B receptors in mammals, following the disappearance of D 1 C receptors in these species.
Print ISSN:
0737-4038
Electronic ISSN:
1537-1719
Topics:
Biology
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