Cre recombinase, a synthetic intron, woodchuck hepatitis virus post-transcriptional regulatory element (WPRE), bovine growth hormone polyA (bGH pA) and an FRT-flanked PGK-neomycin cassette replace sequences of the mouse Tenm3 gene immediately 3' of the ATG transcriptional start site in exon 1 via homologous recombination in embryonic stem cells. The neomycin cassette was retained.The mutation functions as a Tenm3 null allele lacking protein expression. (J:257337)