An autosomal dominant mutation of facial development in a transgenic mouse

We have created a transgenic mouse which showed an autosomal dominant mutation of facial development. This facial malformation was characterized by a short snout and a twisted upper jaw. All offspring showing the dysmorphic phenotype carried the injected gene. In order to analyze the primary cause of this mutation, newborn mice and embryos were examined. The outcome was that the malformation of nasal and premaxillary bone was not the primary defect but was a secondary event. The primary cause of this dysmorphism was a developmental defect in the first branchial arch. Genomic DNA fragments flanking the insertion site of this mutant mouse were cloned. Using these fragments, we have assigned the integration site to chromosome 13. The gene responsible for a previously reported mutant mouse, one which also has a short snout, is also reported to be on chromosome 13. In the fragments flanking the insertion site of the transgenic mouse, at least one fragment was highly conserved in mammals. These results indicate that this malformation is due to the insertional disruption of a host gene. However, the possibility that this mutation is caused by an inappropriate expression of the injected gene still remains to be investigated.