Exons 2-3 and part of exon 4 (encoding the ectodomain and 3 putative glycosaminoglycan attachment sites) were replaced with a neo-derived cassette via homologous recombination. Absence of gene expression in homozygous mutant animals was confirmed by Northern blot and Western blot analysis of total kidney RNA and fibroblast lysates, respectively. (J:60596)