Regulation of vimentin gene expression in the ocular lens

Vimentin expression in the lens is striking due to the reported mesenchymal preference of vimentin and the epithelial origin of the lens. The amount of chicken vimentin mRNA levels determined by Northern blot analysis increased 3-fold from 7 to 14 days of embryonic lens development and then decreased 10-fold at 16 days of development, suggesting that post-transcriptional processes may contribute to the level of cytoplasmic vimentin mRNA during lens development. To analyze the mechanisms governing vimentin gene expression in the lens at the level of transcription, a series of chicken vimentin 5'-flanking region deletions were fused to the bacterial CAT gene and transfected into fibroblasts and lens cultures derived from three species. The -160 to +1 sequence conferred equal promoter activity in cultured chicken lens epithelial cells and fibroblasts. The -321 to -160 sequences increased promoter activity in all cultures, but more strongly in fibroblasts than in lens cells. Sequence elements in the region -608 to -321 repressed promoter activity in lens cells and fibroblasts. Promoter activity was partially restored in fibroblasts but not in lens cells by -767 to -608 sequences. Vimentin gene expression in the lens thus appears to be controlled by multiple positive- and negative-acting elements in its 5'-flanking sequence.