This allele is a derivative of Sema3ctm1Jra in which the neomycin resistance gene was removed by Cre mediated recombination by crossing mice that carry the Sema3c allele to mice that express Cre recombinase in the germ cell. mRNA in homozygous mutant E12.5 embryos was barely detectable by in situ hybridization. RT-PCR analysis of these embryos detected transcript from regions 5' and 3' of the targeted sequences, but did not detect transcript from a region internal to the targeted sequences.