[Establishment of osteoblast-specific Cre transgenic mice]

An osteoblast-specific Cre transgenic construct (pOC-Cre) containing the osteocalcin promoter, Cre recombinase gene and polyA of human growth hormone gene was generated. The 4.6 kb DNA fragment of OC-Cre was introduced into fertilized zygotes by microinjection. 2 out of 16 offspring were identified as founders carrying the transgene by PCR and Southern blot analysis, and the integration efficiency is 12.5 %. To check the tissue distribution of the OC-Cre, the OC-Cre transgenic founder mice were bred with the mice carrying Smad4 conditional alleles. PCR results showed that the genomic DNA fragments after Cre mediated recombination could be only amplified from bone tissues of the transgenic mice. LacZ staining of OC-Cre; ROSA26 double transgenic mice revealed that Cre recombinase expressed in osteoblasts and mediated DNA recombination between LoxP sites at the ROSA26 locus. All these data indicated that the Cre recombinase was ex-pressed in the osteoblasts of the OC-Cre transgenic mice and could mediate DNA recombination between LoxP sites. The OC-Cre transgenic mice we generated in this study could serve as a useful tool for generating osteoblast specific gene-knockout mice.