A gene trap vector inserted into intron 1. RT-PCR analysis of spinal cord RNA confirmed that no detectable full length transcript is expressed from this allele. Reverse transcriptase-PCR amplification of spinal cord RNA identified a Lix1 alternative transcript beginning in intron 4 and containing exons 5 and 6. The alternative transcript appeared to be rodent specific, and its expression was not disrupted in homozygous KO mice.