UPSTREAM REGULATORY ELEMENTS NECESSARY FOR EXPRESSION OF THE RAT COL1A1 PROMOTER IN TRANSGENIC MICE

The activity of fusion genes containing fragments of the COL1A1 promot er was measured in tissues from 6- to 8-day-old transgenic mice. ColCA T3.6 contains approximately 3.6 kb (-3521 to 115 bp) of the rat COL1A1 gene, the chloramphenicol acetyltransferase (CAT) reporter gene, and the SV40 splice and polyadenylation sequences. ColCAT2.3 and ColCAT1.7 are deletion constructs that contain 2296 and 1667 bp of COL1A1 upstr eam from the RNA start site, respectively. For each transgene, up to s ix lines of mice were characterized. Both ColCAT3.6 and ColCAT2.3 had similar activity in bone and tooth; ColCAT1.7 was inactive. In transge nic calvariae, levels of transgene mRNA paralleled levels of CAT activ ity. In tendon, the activity of ColCAT2.3 was 3- to 4-fold lower than that of ColCAT3.6, and the activity ColCAT1.7 was 16-fold lower than t hat of ColCAT2.3. There was little activity of the ColCAT constructs i n liver and brain. These data show that DNA sequnces between -2.3 and -1.7 kb are required for COL1A1 promoter expression in bone and tooth; sequences that control expression in tendon are distributed between - 3.5 and -1.7 kb of the promoter, with sequences downstream of -1.7 kb still capable of directing expression to this tissue. The cis elements that govern basal expression of COL1A1 in transgenic calvariae appear to be different from those required for optimal expression of the COL 1A1 promoter in stably transfected osteoblastic cells.