UBC Theses and Dissertations
Genetic and epigenetic factors in a mouse model for multifactorial cleft lip Plamondon, Jenna Ashley
Cleft lip (CL/P) is a human birth defect with complex genetic etiology. Two loci are involved in CL/P in the A/WySn mouse model: Wnt9b on Chromosome 11 and clf2 on Chromosome 13. There are two known mutant alleles at Wnt9b; clf1 is a spontaneous recessive mutation caused by an insertion of an IAP transposon near the gene Wnt9b and the second allele is a Wnt9b knock out. Clf2 is the second locus required for the CL/P phenotype. Quantitative PCR was used to investigate expression of other genes that might be affected by the absence of Wnt9b expression. Expression levels of Bmp4, Dkk1, Msx1, Msx2, Raldh3, Sox11, Wnt3, Wnt4 and β-catenin were examined. This experiment detected a significant decrease in expression levels of β-catenin in Wnt9bNull/Null embryos. The clf2 gene has not yet been identified and the function was unknown. Segregants from multi-generation crosses using the Wnt9b knockout, “Cross 1” and “Cross 2”, were examined for CL/P and genotype at polymorphic markers linked to Wnt9b and clf2 to ask whether clf2 modifies the frequency of CL in the Wnt9b null homozygotes. I also used recombinants from a congenic stock, consulted the mouse genome assembly and examined ancestral haplotypes in a strain survey to define the clf2 candidate region and examined mouse genome databases to develop a candidate gene list. My studies have reduced the clf2 candidate region to a 3.0 mb region between Cntnap3 and Ak029746. This region contains 48 genes and a majority of them encode zinc finger proteins. The specific crosses gave unexpected results that interfered with the ability to study the effect of clf2 genotype on penetrance of CL/P; the limited data suggested that clf2 does not affect penetrance of CL/P in the Wnt9b null embryos. However, Cross 2 provided an inverse way to address the role of clf2: to test whether clf2 modifies the methylation of the IAP transposon at Wnt9b in the clf1 mutant allele. Using the COBRA technique we studied the methylation levels of the IAP in Wnt9bclf1/Null embryos segregating at clf2. The results indicated that clf2 modifies the methylation status of the IAP.
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