BIOCHEMICAL-IDENTIFICATION AND TISSUE-SPECIFIC EXPRESSION PATTERNS OFKERATINS IN THE ZEBRAFISH DANIO-RERIO

We have identified a number of type I and type II keratins in the zebr afish Danio rerio by two-dimensional polyacrylamide gel electrophoresi s, complementary keratin blot-binding assay and immunoblotting. These keratins range from 56 kDa to 46 kDa in molecular mass and from pH 6.6 to pH 5.2 in isoelectric point. Type II zebrafish keratins exhibit si gnificantly higher molecular masses (56-52 kDa) compared with the type I keratins (50-48 kDa), but the isoelectric points show no significan t difference between the two keratin subclasses (type II: pH 6.0-5.5; type I: pH 6.1-5.2). According to their occurrence in various zebrafis h tissues, the identified keratins can be classified into ''E'' (epide rmal) and ''S'' (simple epithelial) proteins. A panel of monoclonal an ti-keratin antibodies has been used for immunoblotting of zebrafish cy toskeletal preparations and immunofluorescence microscopy of frozen ti ssue sections. These antibodies have revealed differential cytoplasmic expression of keratins; this not only includes epithelia, but also a variety of mesenchymally derived cells and tissues. Thus, previously d etected fundamental differences in keratin expression patterns between higher vertebrates and a salmonid, the rainbow trout Oncorhynchus myk iss, also apply between vertebrates and the zebrafish, a cyprinid. How ever, in spite of notable similarities, trout and zebrafish keratins d iffer from each other in many details. The present data provide a firm basis from which the application of keratins as cell differentiation markers in the well-established genetic model organism, the zebrafish, can be developed.