Changes in the Nuclear and Cytoplasmic Levels of Type I and Type I1 Collagen RNAs during Growth of Chondrocytes

Chick embryo chondrocytes were grown in cell culture in the presence of 5-bromo-Z’-deoxyuridine. Under these conditions, the cells attached to the tissue culture plates and became polygonal in shape and concurrently shifted their synthesis of collagen from type I1 to type I subunits. The changes in the levels of the corresponding collagen RNAs in the nucleus and cytoplasm were examined during this shift by dot blot and Northern blot analyses. It was found that the expression of the cartilage collagen gene, al(II), was controlled at the transcriptional level. While the type I collagen genes may also be partially controlled at the transcriptional level, both genes appear to be transcribed in chondrocyte nuclei although chondrocytes do not synthesize type I collagen. In these chondrocytes, the transcripts of the &(I) gene are polyadenylated and are apparently exported to the cytoplasm but are not translated.