CYTOSKELETAL AND NUCLEAR-LOCALIZATION OF MYELIN OLIGODENDROCYTIC BASIC-PROTEIN ISOFORMS

The recently described single copy Myelin-associated Oligodendrocytic Basic Protein (Mobp) gene is expressed exclusively in the central nerv ous system (CNS). The gene encodes a family of small highly basic poly peptides with predicted amino acid lengths of 69, 71, 81, 99 and 170, all of which share a 68 residue amino terminal. Here we report on the subcellular distribution of two of these polypeptides termed MOBP81 an d MOBP170 in transiently transfected Cos7 cells using an antibody rais ed against a region common to all isoforms of MOBP, Additionally, we d escribe MOBP trafficking in cultured mouse spinal cord oligodendrocyte s. Immunostaining for MOBP81 is intense in the perinuclear region and extends throughout the cytoplasm colocalizing with the microtubular cy toskeletal network. Consistent with this we demonstrate that MOBP part itions with the cytoskeletal fraction prepared from myelin. In contras t, although MOBP170 is present in the cytoplasm it does not colocalize with the cytoskeleton and displays a greater variation in distributio n. In the majority of transfectants immunostaining is present througho ut the karyoplasm but with increased intensity around the nucleolus. W ithin mouse primary oligodendrocytes endogenous MOBP is present in the cell body and processes colocalizing with the microtubular network, I mmunoreactivity is not detectable in the nucleus in these mature oligo dendrocytes. These significant differences in MOBP81 and MOBP170 prote in kinesis coupled to different expression profiles of their respectiv e message populations may be indicative of both myelin structural and cellular/regulatory functions, respectively, for these polypeptides.