Analysis of transcription of the Col6a1 gene in a specific set of tissues suggests a new variant of enhancer region

The region extending from -5.4 to -3.9 kilobase pairs from the transcriptio n start site of the Col6a1 gene has been previously shown to contain sequen ces activating tissue-specific transcription in articular cartilage, interv ertebral disks, subepidermal, and vibrissae mesenchyme and peripheral nervo us system (Braghetta, P., Fabbro, C., Piccolo, S., Marvulli, D., Bonaldo, P ., Volpin, D., and Bressan, G. M. (1996) J, Cell Biol. 135, 1163-1177). Ana lysis of expression of deletions of this region in transgenic mice has iden tified the 383-base pair fragment E-L as the most active sequence of the re gion. Linker-scanning mutagenesis analysis of segment E-J, which spans the 5' 245 base pairs of E-L and is sufficient for high frequency expression in articular cartilage, showed that all the mutations reduced transcription c onsiderably, suggesting that the integrity of the entire cluster of element s is necessary for enhancer activity. Electrophoretic mobility shift assays with nuclear extracts derived from various sources showed that fragment E- J binds numerous transcription factors (at least 22). These factors are pre sent in most cells, expressing and nonexpressing alpha 1(VI) collagen mRNA, but in different relative proportions, and none of them appears to be cell type-specific. Several lines of evidence indicate that sequence elements o f the enhancer may have different functional roles in various cells. The da ta configure the -5.4/-3.9 region of the Col6a1 gene as a new type of tissu e-specific enhancer, characterized by a variety of tissues supporting its a ctivation and by the dependence of its function only on ubiquitous transcri ption factors. This type of enhancer is postulated to be particularly impor tant for genes such as those of the extracellular matrix, which are often e xpressed with broad tissue specificity.