A series of ENU-induced single-base substitutions in a long-range cis-element altering Sonic hedgehog expression in the developing mouse limb bud

Mammal-fish-conserved-sequence 1 (MFCS1) is a highly conserved sequence that acts as a limb-specific cis-acting regulator of Sonic hedgehog (Shh) expression, residing 1 Mb away from the Shh coding sequence in mouse. Using gene-driven screening of an ENU-mutagenized mouse archive, we obtained mice with three new point mutations in MFCS 1: M101116, M10111 7, and M101192. Phenotype analysis revealed that M101116 mice exhibit preaxial polydactyly and ectopic Shh expression at the anterior margin of the limb buds like a previously identified mutant, M100081. In contrast, M10111 7 and M101192 show no marked abnon-nalities in limb morphology. Furthermore, transgenic analysis revealed that the M101116 and MI00081 sequences drive ectopic reporter gene expression at the anterior margin of the limb bud, in addition to the normal posterior expression. Such ectopic expression was not observed in the embryos carrying a reporter transgeDe driven by M101117. These results suggest that M101116 and M100081 affect the negative regulatory activity of MFCSI, which suppresses anterior Shh expression in developing limb buds. Thus, this study shows that gene-driven screening for ENU-induced mutations is an effective approach for exploring the function of conserved, noncoding sequences and potential cis-regulatory elements. (c) 2006 Elsevier Inc. All rights reserved.