Stabilization of the mRNA follows transcriptional activation of type II collagen gene in differentiating chicken chondrocyte

The differentiation of chicken endochondral chondrocyte can be induced in vitro by transferring to suspension culture dedifferentiated chondrocytes grown as adherent cells. During the differentiation process, the synthesis of type I collagen is repressed while the genes encoding type II, IX, and X collagens are gradually activated. The changes in the steady-state levels of the mRNAs for type I, IX, and X collagens were shown to be fully accounted for by proportional modifications in the rates of specific gene transcription (Castagnola, P., Dozin, B., Moro, G., and Cancedda, R. (1988) J. Cell Biol. 106, 461-467). In the present report, we demonstrate that the cellular accumulation of type II collagen mRNA in differentiating chondrocyte is regulated not only at the transcription level but also through a stabilization of the RNA transcript as shown by the enhanced half-life of the mRNA in differentiated cells treated with actinomycin D. We also give evidence that this additional mechanism: 1) is specific for type II collagen, 2) does not occur at an early stage of differentiation when type II collagen mRNA starts accumulating, 3) affects only the cytoplasmic form of the RNA transcript.