TISSUE-SPECIFIC AND DEVELOPMENT-SPECIFIC EXPRESSION IN TRANSGENIC MICE OF A TYPE-I PROCOLLAGEN (COL1A1) MINIGENE CONSTRUCT WITH 2.3 KB OF THE PROMOTER REGION AND 2 KB OF THE 3'-FLANKING REGION - SPECIFICITY IS INDEPENDENT OF THE PUTATIVE REGULATORY SEQUENCES IN THE 1ST INTRON

Previous reports have provided inconsistent data as to the cis-regulatory elements that are essential for correct expression of the gene for the proalpha1 (I) chain of type I procollagen (COL1A1) in the many tissues in which the protein is synthesized. Here, two internally deleted minigene versions of the human COL1A1 gene were used to prepare transgenic mice. The constructs made it possible to test regulatory sequences in the normal context of the gene. Also, in contrast to the reporter genes used in previous experiments, the constructs made it possible to assay quantitatively expression of the exogenous genes relative to expression of the endogenous COL1A1 gene, both as mRNA and as protein. The average level of expression of the minigenes varied among three transgenic lines, but the ratio of expression of the minigenes to expression of the endogenous gene was the same in all transgenic mice of a given line. Within the same line, the ratio of expression was essentially the same in nine or more tissues in which expression of the endogenous gene varied widely. Also, the ratio of expression within a given line was the same in 15-day-old embryos and in mice ranging in age from 4 days to 4 months. In addition, the ratio remained constant during repair of a surgical wound. The results demonstrated, therefore, that the minigene constructs with about 2.3 kb of the promoter region and about 2 kb of the 3'-flanking region contained all of the sequences necessary for correct expression of the genes in a tissue-specific and development-specific manner. Assays of a line of transgenic mice expressing the minigene with the deletion in the first intron demonstrated that the first intron of the COL1A1 gene had no discernible effect on the specificity of expression. Therefore, the results did not support previous data suggesting that the relatively large first intron of the gene contains important regulatory sequences.