Molecular Genetics of X-Linked Cataracts: Quantitative Expression of Xcat Candidate Genes

Abstract

Abstract: : Nance-Horan syndrome (NHS; MIM302350) also called cataract-dental syndrome, is a rare X-linked disease characterized by severe bilateral congenital cataracts, microphthalmia, microcornea and dental and bone anomalies. Linkage studies have refined the NHS disease locus to a 3.5 cM interval on human Xp22.2. The Xcat mouse is a model for human NHS because 1) the mice display X-linked cataracts and 2)the Xcat locus has been localized between markers DXMit20 and DXMit121, a region syntenic with human Xp22.2. Purpose: We examined the expression and sequence of retinoic acid inducible gene 2 (RAI2) in Xcat neonate eyes. The mouse RAI2 gene maps between markers DXMit121 and DXMit20 and is therefore an Xcat candidate gene. Methods: RNA was isolated from neonate (P0) eyes, reverse transcribed and the cDNA was used as templates for quantitative real time PCR using ABI Prism TaqMan reagents. The PCR was performed on an ABI Prism 7900HT sequence detection system. In addition, the RAI2 gene was PCR amplified from Xcat genomic DNA using RAI2 specific primers. These PCR products were then sequenced to detect the presence of mutations. Results: Within the RAI2 coding region, the DNA sequences in normal and Xcat mice were identical. We found that the RAI2 transcript was expressed in both normal and Xcat neonate eyes. The expression level of RAI2 in Xcat eyes was indistinguishable from normal mouse eyes. Conclusions: The sequence and transcript level of RAI2 was normal in Xcat mice. These results indicate that mutations in the RAI2 regulatory or coding regions are not causative of the congenital cataract phenotype in Xcat mice.

Keywords: gene mapping • cataract • animal model