INSERTIONAL MUTATION OF THE MOUSE MSX1 HOMEOBOX GENE BY AN NLACZ REPORTER GENE

We have generated a null allele of the mouse Msx1 homeobox gene by ins ertion of an nlacZ reporter gene into its homeobox. The sensitivity of beta-galactosidase detection permitted us to reveal novel aspects of Msx1 gene expression in heterozygous embryos, in particular in ectoder m and mesoderm during gastrulation, and in migrating neural crest cell s. Homozygous mutant mice die at birth with facial defects (see Satoka ta, I, and Maas, R. (1994) Msx1 deficient mice exhibit cleft palate an d abnormalities of craniofacial and tooth development. Nat. Genet. 6, 348-356). To investigate the reason for this limited phenotype, we com pared the pattern of Msx1 expression with that of the closely related Msx2 gene in wild type embryos and in Msx1(-/-) mutants. Notably, wher eas the expression of Msx1 and Msx2 overlap in the developing limb, th is is not the case in the facial regions most affected in the mutant. (C) 1997 Elsevier Science Ireland Ltd.