A new allele of Gli3 and a new mutation, circletail (Crc), resulting from a single transgenic experiment.

While generating transgenic lines, transgene-linked mutations can occur, which are caused by an insertional mutation at a given locus. More rarely, mutations unlinked to the transgene insertion site are observed. In the process of generating a mouse overexpressing the enzyme tyrosinase, we have obtained one transgenic line that appears to carry a semidominant insertional mutation at the Gli3 (extra toes) locus, characterized by polydactyly and skeletal malformations. Additionally, the transgenic line contained a second mutation, Crc (circletail), which appears to be unlinked to the transgene insertion site. Heterozygous Crc mice are incompletely penetrant for a circled-tail phenotype, while all homozygous Crc/Crc mice die at birth of a severe neural tube defect (craniorachischisis). Anatomical evidence from a Crc/Crc; Gli3/+ fetus indicates that these two genes may interact.