Enhancer-independent promoter activity of the mouse alpha B-crystallin/small heat shock protein gene in the lens and cornea of transgenic mice

The alpha B-crystallin/small heat shock protein gene is expressed very high ly in the mouse eye lens and to a lesser extent in many other nonocular tis sues, including the heart, skeletal muscle and brain. Previously we showed in transgenic mice that lens-specific alpha B-crystallin promoter activity is directed by a proximal promoter fragment (-164/+44) and that non-lens pr omoter activity depends on an upstream enhancer (-427/-259) composed of at least 5 cis-control elements. Here we have used truncated alpha B-crystalli n promoter-CAT transgenes to test by biphasic CAT assays and/or histochemis try for specific expression in the cornea and lens. Deletion either of 87 b p (-427/-340) from the 5' end of the alpha B-crystallin enhancer or of the whole enhancer (-427/-258) abolished alpha B-crystallin promoter activity i n all tissues except the lens and corneal epithelium when examined by the b iphasic CAT assay in 4-5-week-old transgenic mice. These truncations also l owered promoter strength in the lens. The -426/+444-CAT, - 339/+44-CAT and - 164/+44-CAT (previously thought to be lens-specific in transgenic mice) t ransgenes were all expressed in the 4-6-week-old corneal epithelium when ex amined histochemically. Immunohistochemical staining confirmed the presence of endogenous alpha B-crystallin in the mature corneal epithelial cells. C AT gene expression driven by the alpha B-crystallin promoter with or withou t the enhancer was evident in the embryonic and 4-6-week-old lens. By contr ast, activity of the alpha B-crystallin promoter/enhancer-CAT transgene was not detectable in the corneal epithelium before birth. Taken together, the se results indicate that the intact enhancer of the alpha B-crystallin/smal l heat shock protein gene is required for promoter activity in all tissues tested except the lens and cornea. (C) 2000 Elsevier Science Ireland Ltd. A ll rights reserved.