Expression of Fibroblast Growth Factor Receptors atDifferent Stages of Differentiation inChick Embryo Chondrocytes

Purpose:Proliferative chondrocytes and prehypertrophic chondrocytes secrete significant amounts of type II collagen in an extracellular matrix. In contrast, hypertrophic chondrocytes secrete type X collagen. In addition, fibroblast growth factors (FGFs) and fibroblast growth factor receptors (FGFRs) also appear to play an important role during differentiation. Accordingly, the current study identified and characterized the chondrocytes and FGFR mRNA expressed at different stages of differentiation. Methods:Chondrocytes were isolated from the caudal one-third portion (LS) of the sterna, peripheral regions (USP) and central core regions (USC) of the cephalic portion of the sterna, and the lower portion of the proximal tibial growth plate (Ti). Chondrocytes from the LS, USP, USC, and Ti of 17-day-old chick embryo sterna and tibia were cultured and type II and type X collagen mRNA and FGFR1, FGFR2, and FGFR3 mRNA were isolated and analyzed by Northern blotting. Results:Generally, the cells were larger in size after two days of culture than after seven days of culture and the cells from the USC and Ti were larger and more mature than those from the LS and USP. Type II collagen genes were found to be expressed in all the chondrocyte types, while type X collagen was strongly expressed in the USC and Ti. Therefore, the LS was identified as a resting or proliferative zone, the USP as a postproliferative or prehypertrophic zone, and the USC or Ti as a hypertrophic zone. FGFR1 was expressed only in hypertrophic chondrocytes in proportion to the culture time, FGFR2 was not expressed in any of the chondrocyte types, and FGFR3 was expressed in all the chondrocyte types. Conclusion:As such, it is possible that the different receptors play distinct roles during chondrocyte differentiation. (Korean J Pediatr 2004;47:439-447)