Mapping Data

Experiment

• Experiment
  TEXT-Congenic
• Chromosome
  15
• Reference
  J:245519 Li BI, et al., Congenital Cataract in Gpr161vl/vl Mice Is Modified by Proximal Chromosome 15. PLoS One. 2017;12(1):e0170724
• ID
  MGI:6115337

Genes

Gene	Assay Type
Modvl4	visible phenotype
Cdh6
Ank
Trio

Notes

• Experiment
  The current study presents a multigenic mouse model of congenital cataract.
  
  To understand the causes of congenital cataract, the vacuolated lens (vl) mouse mutant has been studied. The vl mutation arose spontaneously on the C3H/HeSnJ (C3H) inbred background. The vl locus was positionally cloned to an 8 bp deletion in the orphan G-protein coupled receptor, Gpr161. The deletion shifts the open reading frame, which truncates the receptor at the C-terminal intracellular domain. The truncation causes reduced steady state protein levels and a disruption of receptor mediated endocytosis, suggesting that the Gpr161^vl allele is a hypomorphic mutation. Consistent with the cataract phenotype, Gpr161 is expressed throughout lens development.
  
  Homozygous C3H-Gpr161^vl mice display congenital cataract with 100% penetrance. Of post-weaning adults, more than 95% show visible bilateral cataracts whereas the remaining show unilateral cataract. In addition, homozygous vl/vl mutants display neural tube defects (NTDs, 100% penetrance), embryonic lethality (~36% penetrance) and belly spot phenotype (<5% penetrance). Interestingly, genetic background modifies the homozygous Gpr161^vl mutant phenotypes. In homozygous F2 progeny of a previous intersubspecific cross between Gpr161^vl and MOLF/EiJ the incidence of congenital cataract was decreased by 85%, along with a total rescue of embryonic lethality and 40% increased incidence of belly spot phenotype. [J:131929].
  
  In the current study, the previously identified QTL, Modvl4 (Chr15; LOD = 4.4) was characterized [J:14556]. Genotyping and morphological analyses demonstrated that the MOLF/EiJ-Modlv4 QTL allele partially rescues the homozygous Gpr161^vl congenital cataract. To further delimit the modifying region, three subcongenic lines were generated which narrowed down the interval to 18 protein-coding genes and 2 miRNAs.
  
  A C3.MOLF-Gpr161^vlModvl4^MOLF/EiJ congenic was generated. To narrow down the interval, Modvl4 congenics, C3.MOLF-Modvl4^MOLF/EiJ mice were further backcrossed to C3H isogenic mice. Subcongenic progeny with recombination breakpoints within the Modvl4 95% CI were selected by genotyping 14 SSLP markers spanning Modvl4.
  
  Three subcongenic lines were generated:
  Sub1, C3.MOLF-(D15Mit81-D15Mit204)^MOLF/EiJ;
  Sub2, C3.MOLF-(D15Mit51-D15Mit204)^MOLF/EiJ; and
  Sub3, C3.MOLF-(D15Mit204-D15Mit257)^MOLF/EiJ.
  
  Two of them (Sub1 and Sub2) contained the MOLF background for proximal Modvl4 but differed in the proximal breakpoint, whereas the third line (Sub3) contained the MOLF background for distal Modvl4. [S1]. Both of the Sub1 and Sub2 homozygotes rescued the cataract phenotype while the Sub3 congenic had no effect, indicating that the MOLF background within either Sub1 or Sub2 was sufficient to partially rescue Gpr161^vl/vl associated cataract in a recessive manner. Because Sub1^MOLF was smaller than Sub2^MOLF and had the same rescuing effect as Sub2^MOLF, subsequent analyses focused on Sub1^MOLF.
  
  To more precisely define the position of the recombination breakpoints, genomic DNA of the two subcongenic lines was genotyped for 11 additional SSLP and SNP markers. The analysis demonstrated that the proximal border was between Chr15: 13062568-13100445 while the distal border was between Chr15: 27443957 28269407. Therefore, the modifier interval that rescued the cataract phenotype was delimited to a 15 Mb region between Chr15:13062568 and Chr15:28269407 [Fig 3B].
  
  The interval 15:13062568-28269407 was searched in UCSC Genome Browser (http:// genome.ucsc.edu/cgi-bin/hgGateway; GRCm38/mm10 assembly) and Ensembl Genome Browser (http://www.ensembl.org; Build 75). Interestingly, a large part of the 15 Mb interval, flanked by rs45839473 and rs32933300, fell into a gene desert and only 20 genes were annotated for both genome browsers (Fig 3C; Also see Table 1 for descriptions of each gene).
  
  Next, to identify the candidate genes and genetic variations from the 20 genes that could be responsible for rescuing the lens fiber and cataract phenotypes, four criteria were used: expression analysis, biological relevancy to lens development and Gpr161 signaling, SNP and Indel analysis and published functional studies. Among all 20 genes situated in the region, three genes, Cdh6, Ank and Trio, were determined candidate genes by the multiple criteria analysis.