Ependymins from the cerebrospinal fluid of salmonid fish: gene structure and molecular characterization

Abstract

So far, ependymins (Epds) have been sequenced only from cypriniform fish, and in the past all attempts have failed to characterize, on a molecular level, homologous Epd proteins in higher vertebrates. Therefore, rainbow trout (Oncorhynchus mykiss) Epds, which represent the predominant proteins of the cerebrospinal fluid, have been N-terminally sequenced and the encoding cDNA subsequently cloned using the polymerase chain reaction. Surprisingly, only 40-42% of the amino acids are identical with the corresponding sequences from goldfish (Carassius auratus), and no convincing immunological cross-reactivity is observed with an antiserum raised against purified Epds from C. auratus. O. mykiss possesses two highly homologous genes encoding Epds (Om-I, Om-II), a feature typical of a quasi-tetraploid species. Western analysis, using two specific antibodies against Epds from O. mykiss, revealed a variety of different glycosylation variants. In contrast to C. auratus, Epds from O. mykiss probably do not form disulfide-linked dimers. The structure of one Epd gene and its flanking regions have been determined for the Atlantic salmon (Salmo salar). Six exons were deduced by comparison with the corresponding cDNA sequence from O. mykiss (almost 98% homology with Om-II).