A 2.2 kb region of the gene including exons 1 and 2 and part of the promoter region was replaced with a neo resistance cassette via homologous recombination. Absence of gene expression in homozygous mutant animals was verified by Western blot analysis of heart, adipose, and lung tissue, and also of mouse embryonic fibroblasts cultured from E13.5 homozygous mutant embryos. (J:75193)