Kinetics of tamoxifen‐regulated Cre activity in mice using a cartilage‐specific CreER^T to assay temporal activity windows along the proximodistal limb skeleton

Abstract

Cartilage differentiation occurs over a broad time range from early embryonic development, when the mesenchymal condensations that give rise to cartilage models for future bone first appear, and continuing through adult life, when there is ongoing maintenance of articular joint surfaces and re-activation of cartilage formation after fracture. The chondrogenic response also figures in the pathogenesis of degenerative and inflammatory joint diseases. We have generated a transgenic line expressing tamoxifendependent Cre recombinase that gives efficient recombination in the chondrogenic lineage, both during embryogenesis and postnatally, and provides a valuable tool for analysis of gene function selectively in chondrogenic cells using conditional genetic approaches. Because the cartilage model of the limb skeleton forms progressively in a proximodistal order during discrete, well-defined time periods, evaluation of the spatial extent of tamoxifen-induced recombination along the limb axis during these time windows has also enabled us to examine the pharmacokinetics of single-dose tamoxifen injections during pregnancy.

A mouse model of chondrocyte-specific somatic mutation reveals a role for Ext1 loss of heterozygosity in multiple hereditary exostoses

“…It has been reported that transgenic Col2a1 promoters tend to be expressed not only in chondrocytes but also in early perichondrial progenitors (30). However, activation of the Col2a1-Cre ERT transgene used in this study in perichondrial cells does not occur unless the transgene is induced with tamoxifen before E13 when chondrogenic and perichondrial precursors are not yet segregated (25). Indeed, we have never observed lacZ + labeling in the perichondrium of R26R;Col2-Cre ERT mice (see Results).…”

“…The Col2-Cre ERT transgene used in this study has been reported to exhibit a low-level leakiness (25). Thus, we hypothesized that the phenotypes observed in Ext1-SKO mice are caused by leaky Cre activity.…”

“…To test the hypothesis that inactivation of Ext1 occurring in a small fraction of chondrocytes is the pathogenic mechanism of MHE, we used a method of stochastic inactivation of loxPflanked Ext1 alleles (Ext1 F ) using a tamoxifen-dependent Cre transgene driven by the Col2a1 promoter (Col2-Cre ERT ) (25). We originally intended to control the level of recombination using different doses of tamoxifen.…”

Characterization of a novel Fibroblast growth factor 10 (Fgf10) knock-in mouse line to target mesenchymal progenitors during embryonic development

“…This is because Fgf10-positive cells are exclusively labeled upon tamoxifen injection, after which labeled cells can be traced and characterized. A previous report has shown that intraperitoneally administered tamoxifen reaches effective levels in the embryonic circulation within 12 hours, after which it is cleared from the pregnant female within 12 hours [18]. This 24-hour time frame allows accurate labeling of Fgf10-positive cells.…”

Indian Hedgehog produced by postnatal chondrocytes is essential for maintaining a growth plate and trabecular bone

“…Cre recombinase fused to a mutated estrogen receptor protein was driven by the col2␣1 promoter were generated as reported earlier (21) and are described in Materials and Methods and shown schematically in Fig. 1A.…”