Abstract
Purpose :
Transmembrane protein 135 (TMEM135) is a key protein involved in retinal pigmented epithelium (RPE) health. For instance, mice with overexpression of Tmem135 (Tmem135 TG) exhibit RPE degeneration. Intriguingly, RPE degeneration caused by overexpression of Tmem135 is influenced by the genetic background of mice, indicating the presence of genetic modifiers. For example, Tmem135 TG mice congenic on the C57BL/6J (B6) background develop RPE degeneration whereas Tmem135 TG mice congenic on the FVB/NJ (FVB) background do not develop RPE degeneration. In this study, we sought to identify major quantitative trait loci (QTLs) that affect RPE degeneration induced by Tmem135 overexpression in mice.
Methods :
RPE flat mounts of 120 N2 progeny mice from F1 B6xFVB Tmem135 TG X B6 WT backcrosses were scored from 0 to 4 based on the severity of their RPE degeneration. DNA samples from these mice were genotyped using the Mouse Universal Genotyping Array (Neogen GeneSeek) where 2,694 single nucleotide polymorphisms were used for the QTL analysis that distinguished between B6 and FVB backgrounds. QTL analysis was performed using the R/qtl analysis package.
Results :
We have identified one significant modifier locus on chromosome 1 (peak LOD score=3.58, P=0.023 by permutation test). We named this modifier on chromosome 1 the modifier of Tmem135 RPE degeneration 1(Mtmrd1). Remarkably, the analysis of genetic interaction by R-qtl revealed a significant epistatic interaction between loci on chromosome 1 and 16 (peak LOD score=6.16). 78.2% of mice carrying heterozygous B6/FVB alleles on both chromosomes 1 and 16 show normal RPE, while only 16.6% of mice carrying homozygous B6 alleles at both loci show normal RPE. We also named the modifier on chromosome 16 the modifier of Tmem135 RPE degeneration 2 (Mtmrd2).
Conclusions :
Our QTL analysis revealed two interacting genetic modifiers (Mtmrd1 and Mtmrd2) responsible for the RPE phenotypic differences between Tmem135 TG mice on the B6 and FVB backgrounds. Further bioinformatic analysis and identification of these two genetic loci will provide multiple novel entry points into the molecular pathways through which Tmem135 overexpression leads to RPE degeneration in mice.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.