The locus was disrupted by the insertion of a construct, containing a floxed neo gene and a lacZ gene fused to the transmembrane domain of the mouse Ntrk2 gene. The insertion was made just downstream of the sequences encoding the signal peptide. RT-PCR analysis confirmed the absence of transcript in homozygous mutant mice. Staining of heterozygous embyros showed expression of beta-galactosidase.