The severity of numerous developmental abnormalities can vary widely despite shared genetic causes. Mice deficient in Twisted gastrulation (Twsg1-/-) display such phenotypic variation, developing a wide range of craniofacial malformations on an isogenic C57BL/6 strain background. To examine the molecular basis for this reduced penetrance and variable expressivity, we used exon microarrays to analyze gene expression in mandibular arches from several distinct, morphologically defined classes of Twsg1-/- and wild type (WT) embryos. Hierarchical clustering analysis of transcript levels identified numerous differentially expressed genes, clearly distinguishing severely affected and unaffected Twsg1-/- mutants from WT embryos. Several genes that play well-known roles in craniofacial development were upregulated in unaffected Twsg1-/- mutant embryos, suggesting that they may compensate for the loss of TWSG1. Imprinted genes were overrepresented among genes that were differentially expressed particularly between affected and unaffected mutants. The most severely affected embryos demonstrated increased p53 signaling and increased expression of its target, Trp53inp1. The frequency of craniofacial defects significantly decreased with a reduction of p53 gene dosage from 44% in Twsg1-/-p53+/+ pups (N=675) to 30% in Twsg1-/-p53+/- (N=47, p=0.04) and 15% in Twsg1-/-p53-/- littermates (N=39, p=0.001). In summary, these results demonstrate that phenotypic variability in Twsg1-/- mice is associated with differential expression of certain developmentally regulated genes, and that craniofacial defects can be partially rescued by reduced p53 levels. We postulate that variable responses to stress may contribute to variable craniofacial phenotypes by triggering differential expression of genes and variable cellular apoptosis.
Bibliographical noteFunding Information:
The authors thank Dr. Michael O'Connor, Dr. York Marahrens, Dr. Nathan Springer, and Dr. ChangWon Park for helpful discussions, and Dr. Erik Carlson for advice on Q-PCR. Sox10Cre mice were generously provided by Dr. William Richardson (University College London). This project was supported by R01 DE016601 to A.P., Minnesota Medical Foundation grant #3532-9227-05 to A.P., Undergraduate Research Opportunities Program (UROP) to B.N., a Musculoskeletal Training Grant NIH-NIAMS , T32 AR050938 to C.J.B., and the Ohio State University Comprehensive Cancer Center.
- Neural crest
- Phenotypic variation