TISSUE LIPOPROTEINS REVISITED - NEW PROTEOLIPID PROTEIN GENE FAMILY MEMBERS IN ELASMOBRANCHS

The proteolipids (PLPs) are abundant components of mammalian CNS myeli n. Recombinant DNA methodologies have enabled us to search for evoluti onary antecedents of PLP/DM20. Polymerase chain reactions of Torpedo a nd Squalus brain cDNA were performed with degenerate primers designed according to the mammalian PLP/DM2D sequence. Three DM20-related produ cts (DM(alpha), DM(beta), and DM(gamma)) were amplified; no cDNAs cont aining the PLP-specific segment were found. Regions of the DM(alpha) a nd DM(gamma) are similar to the pore-forming segments of certain ligan d-gated channels. In embryonic Squalus CNS, DM(alpha) and DM(gamma) ap pear to be co-expressed with Po. Antiserum raised against Torpedo DM(a lpha) recognizes a protein in mouse CNS myelin, demonstrating that at least one of the newly recognized fish DMs is also in mammals. Our dat a, as well as that of other laboratories, supports the existence of a ubiquitously expressed proteolipid gene family.