TISSUE-SPECIFIC EXPRESSION OF THE GENE FOR TYPE-I PROCOLLAGEN (COL1A1) IN TRANSGENIC MICE - ONLY 476 BASE-PAIRS OF THE PROMOTER ARE REQUIRED IF COLLAGEN GENES ARE USED AS REPORTERS

Inconsistent data have been reported on the size of the promoter that is necessary for high levels of tissue-specific expression of the COL1 A1 gene for type I procollagen. Some of the inconsistencies may be tra ced to the use of reporter gene constructs. Therefore, we prepared tra nsgenic mice with modifications of the intact gene engineered so that the level of expression of the transgene could be assayed both as mRNA and protein that were similar to the products from the endogenous COL 1A1 gene. The results with a mini-COL1A1 gene lacking 41 internal exon s and introns indicated that the first intron and 90% of the 3'-untran slated region were not essential for tissue-specific expression. In a hybrid COL1A1/COL2A1 construct, a 1,9-kilobase 5'-fragment from the CO L1A1 gene that contained only 476 of the promoter was linked to a prom oterless 29.5 kilobase fragment of the human COL2A1 gene for type II p rocollagen. The hybrid COL1A1/COL2A1 construct was expressed as both m RNA and protein in tissues that normally synthesize type I procollagen but not type II procollagen. Apparently, 476 base pairs of the promot er are sufficient to drive tissue-specific expression of the COL1A1 ge ne and totally inappropriate expression of the COL2A1 gene.