Partial characterization of the 5'-flanking region of trout IP: A Po-like gene containing a PLP-like promoter

Abstract

The IP gene of trout encodes two Po-like glycoproteins which are expressed by oligodendrocytes in the fish CNS, A 679 bp fragment of its 5'-flanking region was isolated from a genomic library and sequenced. The transcription start point was determined 124 bp upstream the ATG initiator codon by primer extension analysis, Apart from a modified TATA-box and an inverted CCAAT-box located at canonical distances from the transcription start site several eucaryotic cis-acting regulatory elements were identified in the 679 bp upstream region, including an AP-1 binding site, a brain specific Sp1 motif, a cyclic AMP responsive element and a consensus sequence for POU homeodomain protein binding, The occurence of respective DNA-binding proteins for Sp1, AP-1 and POU in the nuclei of trout oligodendrocyte progenitor cells was verified by gel retardation experiments, Functional activity of various subfragments of the 679 bp upstream region was demonstrated by CAT reporter gene analysis, A computer-assisted sequence alignment of the trout IP 5'-flanking end with the corresponding region of the mammalian PLP gene promoter revealed four sites of high homology, while similarity with the mammalian Po gene promotor was low. The results are discussed with respect to the phylogenetic shift from Po-like proteins to PLP during evolution of the vertebrate CNS myelin sheath. (C) 1997 Wiley-Liss, Inc.