These mice express Cre recombinase under the control of the mouse homeobox B6 (Hoxb6) lateral plate mesoderm (LPM) enhancer region. HOXB6 is a transcription factor that regulates anterior-posterior axis positioning during development. Hoxb6-Cre is expressed throughout the lateral plate mesoderm at E8.5, in mesoderm of the hindlimb bud at E9.5, and in the entire hindlimb by E11.5. In the forelimb, Cre activity is detected at the posterior end during limb initiation and then extends anterior until nearly the entire limb bud is positive by E11.5. Homozygotes are viable and fertile. When crossed with a strain containing a loxP site-flanked sequence, Cre-mediated recombination results in deletion of the flanked sequence in Cre-expressing tissues of the offspring.
For example, when bred to a strain expressing a floxed-fibroblast growth factor receptor 1 (Fgfr1) gene, the resulting mice exhibit malformed hindlimbs and abnormal posterior portions of the forelimbs. The limb buds display reduced proximal-distal height and increased dorsal-ventral length.
