This allele was generated from Sema3atm1Tyag by transient Cre expression in TT-2 cells. Recombination produced three alleles, Sema3atm1.1Tyag, Sema3atm1.2Tyag and Sema3atm1.3Tyag. The Sema3atm1.3Tyag allele has the first exon deleted and replaced by a lacZ-neo construct flanked by loxP sites.