A Cre knock-in mouse line on the Sickle tail locus induces recombination in the notochord and intervertebral disks.

Sickle tail (Skt) was originally identified by gene trap mutagenesis in mice, and the trapped gene is highly expressed in the notochord, intervertebral discs (IVD), and mesonephros. Here, we report the generation of Skt(cre) mice expressing Cre recombinase in the IVD due to target insertion of the cre gene into the Skt locus by recombinase-mediated cassette exchange. Crossing a conditional lacZ Reporter (R26R), Cre expression from the Skt(cre) allele specifically activates β-galactosidase expression in the whole notochord from E9.5 onwards. In E15.5 Skt(cre);R26R embryos, reporter activity was detected in the nucleus pulposus and in a portion of the annulus fibrosus, resulting in expansion of Cre-expressing cells in the adult IVD. Reporter activity was also seen in the Skt(cre);R26R mesonephros at E15.5. These results suggest that Skt(cre) mice are useful for exploring the fate specification of notochordal cells and creating models for IVD-related skeletal diseases.