CYTOPLASMIC AND NUCLEAR-LOCALIZATION OF MYELIN BASIC-PROTEINS REVEALSHETEROGENEITY AMONG OLIGODENDROCYTES

Myelin basic proteins (MBPs) are major proteins of central nervous sys tem (CNS) myelin, where they facilitate the apposition of cytoplasmic faces of myelin lamellae. Myelin-bearing oligodendrocytes transport MB P mRNA to myelin, where newly translated protein is directly inserted into the myelin sheath, An apparent absence of MBPs in oligodendrocyte perikarya has suggested that MBP localized to the soma is translation ally inert, We now demonstrate by confocal immunofluorescence microsco py that not only are MBPs present in the majority of oligodendrocyte p erikarya but oligodendrocytes are heterogeneous with respect to their localization of MBPs; MBPs are concentrated in some cells at the plasm alemma and distributed in others throughout the cytoplasm and, surpris ingly, the nucleus, MBPs are present in the nuclei of over half of oli godendrocytes in the adult, but in almost all MBP+ oligodendrocytes du ring myelinogenesis, Transport of MBPs into nuclei appears to be a reg ulated process since some cells exhibit robust MBP accumulation in the ir cytoplasm but exclude MBPs from their nuclei, We show that oligoden drocyte nuclei contain all four major MBP isoforms, but that in transg enic mice, the epitope-tagged 14 kD MBP isoform preferentially segrega tes to the plasmalemma, Our data demonstrate that oligodendrocytes are not required to exclude MBPs from their perikarya and suggest that MB Ps have a specific function in the oligodendrocyte perikarya and nucle us. (C) 1996 Wiley-Liss, Inc.