An insertion/deletion TEX28 polymorphism and its application to analysis of red/green visual pigment gene arrays

Abstract

TEX28 gene (fTEX) is present immediately downstream of the red/green visual pigment gene array on the human X chromosome. Its pseudogene (pTEX) that lacks exon 1 is present within the array between pigment genes. We found that both fTEX and pTEX genes had a 697 bp insertion/deletion polymorphism in their introns 3. In color-normal male subjects, the frequency of the 697 bp region was 43% (40/94) in pTEX and 97% (91/94) in fTEX in the array of Red-pTEXGreen-fTEX and 10% (9/94) in pTEX and 87% (41/47) in fTEX in the array of Red-pTEX-Green-pTEX-GreenfTEX. These results suggest that normal arrays with multiple green genes may have arisen through gene duplication rather than unequal homologous crossover. In color-vision-deficient male subjects with a single-gene array, the frequency of the 697 bp region was 83% (25/ 30) in the array of Green-fTEX and 66% (74/112) in the array of Red-fTEX. In color-vision-deficient male subjects with a 2-gene array, the frequency of the region was 44% (16/36) in pTEX and 97% (35/36) in fTEX in the array of Green-pTEX-Green-fTEX and 75% (18/24) in pTEX and 92% (22/24) in fTEX in the array of Red-pTEX-Red-fTEX. These results suggest that 2-green-gene arrays have arisen through unequal homologous crossover between a normal 2-gene array and a single-green-gene array. With data from a longrange PCR method using the insertion/deletion polymorphism, we proposed a structure of the second gene of 3-gene arrays, Green-pTEX-Green-pTEXGreen-fTEX and Red-pTEX-Red-pTEX-Red-fTEX, in color-vision-deficient subjects.

Evaluation of the X-Linked High-Grade Myopia Locus (MYP1) with Cone Dysfunction and Color Vision Deficiencies

“…Few studies on TEX28 have been published, 9–11 and the expression studies we performed revealed that TEX28 is expressed in blood, kidney, and testis at the mRNA level. Although the expression in testis is consistent with previous findings, Chen et al 29 did not report expression in kidney and did not test for expression in blood.…”

“…The realtime assay targeted on the opsin genes confirmed previous predicted findings of opsin gene numbers in the Minnesota pedigree. 4 Only three copies of TEX28 have been reported within the opsin gene array, 9,11 though the real-time assay targeted on the TEX28 gene indicated that the affected male subjects had up to four copies of TEX28 in the BED and five copies in the Minnesota phenotypes in contrast to the 3 copies in the unaffected males. Two families from the United Kingdom showed either fewer (one) or greater (four) number of copies in the affected samples when compared with the unaffected samples.…”

“…Few studies of TEX28 have been reported in the literature, and its involvement in the X-linked myopia phenotypes is unknown. 10,11 The reported number of normal repetitive copies of TEX28 is three, intercalated within and translated in the opposite (3′ to 5′) direction from the opsin gene array. 9 …”

Exploring the association between glucose-6-phosphate dehydrogenase deficiency and color blindness in Southeast Asia

“…For the same reason, relationships observed in one population are unlikely to apply to others. For example, the 697 bp deletion in TEX28 within the opsin locus was associated with red-green color blindness in Japanese [20]. Kanjanawadee et al used this deletion as a molecular marker to study the association between color blindness and G6PD gene in Karen populations from central Thailand.…”

Molecular Genetics of Human Myopia: An Update

“…(87) There are minimal studies on CXorf2 in the literature, and only 3 copies of CXorf2 have been reported within the opsin gene array. (156,157) Figure 3a shows quantification of opsin gene expression by real-time PCR. Expression pattern follows the number of copies previously reported by Young et al (84) Figure 3b shows quantification of CXorf2 gene expression by real-time PCR.…”