Phylogeny and expression divergence of metabotropic glutamate receptor genes in the brain of zebrafish (Danio rerio).

Glutamate, the most abundant excitatory neurotransmitter of the central nervous system, modulates synaptic transmission and neuronal excitability via metabotropic glutamate receptors (mGluRs). These receptors are essential components for diverse cognitive functions and they represent potential drug targets for the treatment of a number of neurological and psychiatric disorders. Here we describe the phylogenetic relation and mRNA distribution of zebrafish mGluRs. In comparison to the eight mglurs present in the mammalian genome, we identified 13 different mglur genes in the zebrafish genome. In situ hybridization experiments in zebrafish revealed widespread expression patterns for the different mglurs in the central nervous system, implicating their significance in diverse neuronal functions. Prominent mglur expression is found in the olfactory bulb, the optic tectum, the hypothalamus, the cerebellum, and the retina. We show that expression pattern of paralogs generated by the teleost-specific whole genome duplication is overlapping in some brain regions but complementary in others, suggesting sub- and/or neofunctionalization in the latter. Group I mglurs are similarly expressed in brain areas of both larval and adult zebrafish, suggesting that their functions are comparable during these stages.