Transgenic mice that express Cre recombinasein hypertrophic chondrocytes

In order to investigate the physiological control of hypertrophic chondrocytes which present the terminally differentiated form of chondrocytes, we generated a mouse line expressing the Cre recombinase under the control of the mouse type X collagen (Col10a1) promoter. In situ hybridization analysis demonstrated the expression of Col10a1‐Cre transgene in hypertrophic chondrocytes of femur at postnatal day 2 (P2). In order to test the excision activity of the Cre recombinase, the Col10a1‐Cre transgenic line was crossed with the mouse strain carrying the Smad4 conditional alleles (Smad4co/co) and the reporter line ROSA26. Multiple tissue PCR of Col10a1‐Cre;Smad4co/+ mice revealed the restricted Cre activity in tissues containing hypertrophic chondrocytes. LacZ staining revealed that the Cre activity was observed in the cartilage primordia of ribs at E14.5 and only detected in the lower hypertrophic region of ribs at P1. These data suggest that the Col10a1‐Cre mouse line described here could be used to achieve conditional gene targeting in hypertrophic chondrocytes. genesis 42:33–36, 2005. © 2005 Wiley‐Liss, Inc.