Levels of expression of the red, green and green-red hybrid pigment genes in the human retina

Abstract

Correlations between the genotype at the X-chromosome-linked red/green pigment genes and the colour vision phenotype will be aided by considering the relative levels of expression of these genes into mRNA and protein in the retina. The red and green pigment genes exist in head-to-tail arrays: one red pigment gene is found 5′ upstream of one or more green pigment genes. In addition to normal red and green pigment genes, 5′green-red3′ hybrid genes, typically associated with deuteranomaly, may also be found in subjects with normal colour vision. A locus control region (LCR), located 5′ upstream of the red pigment gene, is shown to be required for expression of the pigment genes in cone photoreceptors. We hypothesize that the expression of any pigment gene in an array is inversely proportional to its distance from this LCR. Green-red hybrid genes that occupy proximal positions in the array are more likely to be expressed and cause deuteranomaly, whereas those that occupy distal positions are less likely to be expressed, and do not result in defective colour vision.The ratios of expression of the red and green pigment genes in human retinas of donors who have only normal red and green pigment genes shows a wide distribution with a mean of 4:1