A 30-base-pair element in them first intron of SOX9 acts as an enhancer inATDC5

SOX9 is a transcription factor that is essential for chondrogenesis and tes tis differentiation, and haplo-insufficiency of SOX9 causes campomelic dysp lasia, severe skeletal malformation syndrome with variably, penetrant XY se x reversal. Here we demonstrate that in several cell lines that express SOX 9, 30-bp element in the first intron of human SOX9 gene act as a potential enhancer in the ATDC5 chondroprogenitor cell line, despite the apparent abs ence of cell-specific regulatory elements within a 5.5-kb promoter region. Deletion and site-specific mutational analyses reveal that the last 12 bp o f the 30-bp element are critical for transcriptional activity, while 5'-hal f sequences are necessary for full transactivation. Gel retardation assays indicate the possible involvement of several binding factors along the leng th of this element., These results suggest that functionally interdependent elements in the 30-bp enhancer region of the first intron account for basa l expression levels of Sox9 in ATDC5. (C) 2001 Academic Press.