Insertion of Cre into the Pax3 locus creates a new allele of Splotch and identifies unexpected Pax3 derivatives

Pax3 is a transcription factor expressed in the dorsal neural tube and somite of the developing embryo. It plays critical roles in premigratory neural crest cells and in myogenic precursors of skeletal muscle. Pax3-deficient Splotch embryos display neural tube and neural crest defects and lack hypaxial muscles. We have created a new allele of Splotch by replacing the first coding exon with a gene encoding Cre recombinase. This functions as a null allele and no Pax3 protein is detected in homozygous embryos. Heterozygous Pax3(Crer/+) mice display a white belly spot, as do Splotch heterozygotes. Homozygous Pax3(Cre/Cre) embryos are embryonic lethal. We have used Pax3(Cre/+), mice to fate-map Pax3 derivatives in the developing mouse. As expected, neural crest and some somitic derivatives are identified. However, we also detect previously unappreciated derivatives of Pax3-expressing precursors in the colonic epithelium of the hindgut and within the urogenital system. (c) 2005 Elsevier Inc. All rights reserved.