c-Krox binds to several sites in the promoter of both mouse type I collagen genes. Structure/function study and developmental expression analysis.

We have previously shown that c-Krox is a zinc finger protein that can increases the transcriptional activity of the mouse alpha1(I) collagen promoter through its binding to two GC-rich sequences (Galéra, P., Musso, M., Ducy, P., and Karsenty, G. (1994) Proc. Natl. Acad. Sci. U. S. A. 91, 9372-9376). In this report we show that c-Krox can bind to an additional site in the promoter of the alpha1(I) collagen gene and to three sites in the promoter of the alpha2(I) collagen gene, the other gene coding for type I collagen. One of the binding sites present in both promoters is adjacent to the CCAAT box. We have performed a structure/function analysis of c-Krox locating the transactivation domain in the zinc finger and C-terminal domains and the dimerization domain in the C-terminal end of the protein. We also demonstrate that c-Krox is an early response gene, whose expression is detectable as early as 9.5-day postcoitum in mouse embryos. Whole-mount in situ hybridization shows that c-Krox is expressed in dermatomes, the somite derivatives that generate dermis, and section in situ hybridization shows that c-Krox and alpha1(I) collagen mRNAs colocalized in skin but not in bone during development. This result is consistent with the predominant expression of c-Krox in skin in postnatal life. Thus, our findings suggest that c-Krox is one transcription factor controlling the coordinated expression of the two type I collagen genes in skin.