A 182 BP FRAGMENT OF THE MOUSE PRO-ALPHA-1(II) COLLAGEN GENE IS SUFFICIENT TO DIRECT CHONDROCYTE EXPRESSION IN TRANSGENIC MICE

Type II collagen is a major chondrocyte-specific component of the cart ilage extracellular matrix and it represents a typical differentiation marker of mature chondrocytes, In order to delineate cis-acting eleme nts of the mouse pro alpha 1(II) collagen gene that control chondrocyt e-specific expression in intact mouse embryos, we generated transgenic mice harboring chimeric constructions in which varying lengths of the promoter and intron 1 sequences were linked to a beta-galactosidase r eporter gene, A construction containing a 3,000 bp promoter and a 3,02 0 bp intron 1 fragment directed high levels of beta-galactosidase expr ession specifically to chondrocytes, Expression of the transgene coinc ided with the temporal expression of the endogenous gene at all stages of embryonic development. Successive deletions of intron 1 delineated a 182 bp fragment which targeted beta-galactosidase expression to cho ndrocytes with the same specificity as the larger intron 1 fragment, T ransgenic mice harboring a 309 bp Col2a1 promoter lacking intron 1 tes ter sequences showed no beta-galactosidase expression in chondrocytes, Reduction of the 182 bp fragment to a 73 bp subfragment surrounding a decamer sequence previously reported to be involved in chondrocyte sp ecificity, resulted in loss of transgene expression in chondrocytes, W hen the Col2a1 promoter was replaced with a minimal beta-globin promot er, the 182 bp intron 1 sequence was still able to target expression o f the transgene to chondrocytes, We conclude that a 182 bp intron 1 DN A segment of the mouse Col2a1 gene contains the necessary information to confer high-level, temporally correct, chondrocyte expression on a reporter gene in intact mouse embryos and that Col2a1 promoter sequenc es are dispensable for chondrocyte expression.