The A/WySn mouse strain with 15 to 20% penetrance of cleft lip and palate (CLP) is an animal model for human multifactorial CLP. The CLP is due to two unlinked genes that interact epistatically, Wnt9bclf1 and clf2, plus a maternal effect. The Wnt9bclf1 mutation is an IAP transposon insertion. The clf2 gene, with unknown function, was located in a 13.6 Mb region of chromosome 13 containing 145 genes.
To reduce the clf2 candidate region, 1146 mice segregating for A/WySn and C57BL/6J alleles at clf2 were screened for recombinants by simple sequence-length polymorphism haplotypes; recombinants' testcross progeny were typed for CLP and simple-sequence length polymorphisms. To identify the function of clf2, the effect of clf2 genotype on risk of CLP was tested in Wnt9bnull/null knockouts and in compound mutants (Wnt9bclf1/null), and the methylation of the IAP at Wnt9b was assayed in the Wnt9bclf1/null mutants by combined bisulfite restriction analysis.
The location of clf2 was redefined to 3.0 Mb between Cntnap3 and AK029746 containing 48 genes, of which 30 are Zfp genes. The clf2 genotype had no detectable effect on Wnt9bnull/null embryos, but strongly affected risk of CLP and methylation of the IAP in Wnt9bclf1/null embryos. CLP was associated with low levels of methylation of the IAP.
The clf2 gene is the first identified polymorphism that affects the epigenetic methylation and silencing of IAP retrotransposons. This CLP model raises the question of whether parallel epigenetic factors are involved in risk and environmental sensitivity of human CLP. Birth Defects Research (Part A), 2011. © 2011 Wiley-Liss, Inc.