Co-expression of collagen types II and X mRNAs in newly formed hypertrophic chondrocytes of the embryonic chick vertebral body demonstrated by double-fluorescence in situ hybridization.

Collagen types II and X mRNAs have been demonstrated simultaneously in newly formed hypertrophic chondrocytes of embryonic chick vertebral cartilage using a double-fluorescence in situ hybridization technique. Digoxigenin- and biotin-labelled type-specific collagen II and X cDNA probes were used. In the embryonic chick vertebra at stage 45, two different fluorescence signals (Fluorescein isothiocyanate and Rhodamine)--one for collagen type II mRNA, the other for type X mRNA--showed differential distribution of the two collagen mRNAs in the proliferating and hypertrophic chondrocyte zones. Several layers of newly formed hypertrophic chondrocytes expressing both collagen types II and X genes were identified in the same section as two different fluorescent colour signals. Low levels of fluorescent signals for collagen type II mRNA were also detected in the hypertrophic chondrocyte zone. Cytological identification of maturing chondrocyte phenotypes, expressing collagen mRNAs, is easier in sections processed by non-radioactive in situ hybridization than in those subjected to radioactive in situ hybridization using 3H-labelled cDNA probes. This study demonstrates that double-fluorescence in situ hybridization is a useful tool for simultaneously detecting the expression of two collagen genes in the same chondrocyte population.