Lack of functional promoter polymorphisms in genes involved in glutamate neurotransmission

The regulation of genes involved in glutamatergic function is thought to be a critical for many central nervous system processes including memory, learning, synaptic maintenance, and many pathological states. As part of a larger survey into the key regulatory elements in genes of neuro-psychiatric interest, we sought to identify the promoter regions of genes in this broad family, and to identify sequence variants that alter gene expression.

Mutation analysis was carried out on the promoters of 20 genes encoding 13 glutamate receptor subunits, four transporters and three metabolizing enzymes using denaturing high performance liquid chromatography. Thirty-nine different promoter haplotypes were cloned into a luciferase reporter gene vector and tested for differences in their ability to drive transcription in both HEK293t and TE671 cell lines.

We have identified a total of 48 sequence variants in six glutamate receptor subunits, four glutamate transporters and two enzymes. Interestingly, seven promoter sequences gave three or more haplotypes from a single individual, indicating gene duplication. No differences in expression greater than 1.35-fold were found between haplotypes originating from the same or paralogous genes.

The lack of common functional polymorphisms in any of these promoters indicates that expression of glutamate receptors and transporters is unusually tightly controlled, and suggests the possibility that non-coding polymorphisms in these genes are rare and may be unlikely to contribute in a major way to neuro-psychiatric phenotypes. This study represents the world's largest survey of the any group of promoters yet performed for any gene system.