A single nucleotide G-to-A substitution at chr18:5592148 (GRCm38) is located 181 bp downstream of Zeb1 exon 1 and 12 bp downstream of exon 1 of overlapping lncRNA Gm10125 on the opposite strand. This mutation does not affect the adjacent splicing site but does disrupt a predicted Myb binding site. An electrophoretic mobility shift assay demonstrated that a probe carrying this mutation does not interfere with Myb binding, unlike a probe with the wild-type sequence. RT-PCR analysis showed that expression of transcripts containing exons 1a and 2 and exons 2 and 3 were increased compared to wild-type controls.