MOLECULAR ANALYSIS OF THE MONOMERIC GTP-BINDING PROTEINS OF OLIGODENDROCYTES

Vesicle transport plays an important role in the formation of myelin. Transport of proteins, including proteolipid protein and myelin associ ated glycoprotein, from their site of synthesis in the endoplasmic ret iculum in the perikaryon of the oligodendrocytes, to myelin, takes pla ce via carrier vesicles. The mechanisms that regulate vesicle transpor t in oligodendrocytes are largely unknown. The presence of monomeric G TP-binding proteins in myelin and oligodendrocytes suggested the hypot hesis that these proteins participate in the regulation of vesicle tra nsport. In an attempt to identify the Rab and Rho GTP-binding proteins present in oligodendrocytes, a cDNA library specific for these protei ns was generated using a reverse transcriptase-polymerase chain reacti on (RT-PCR) approach. Twelve different clones containing sequences tha t coded for members of the Rab and Rho families of GTP-binding protein s were isolated. This group includes Rab1, -1b, -2, -5b, -5c, -7, -8, -12, -14, -23 and Rho A. One additional clone revealed a novel cDNA se quence. Analysis of the effector loop motif indicated that this sequen ce encodes for a member of the Rab family. We refer to this new sequen ce as Rab0. Comparison of Rab0 with the most similar rat Rab sequences , Rab 14 and Rab 22, and with a recently cloned human Rab22b, showed a 71%, 72% and 94% identity, respectively. By RT-PCR analysis the Rab0 mRNA was found to be mainly expressed in oligodendrocytes and to a les ser extent in oligodendrocyte precursors, astrocytes and microglia. Mo reover, the highest levels of Rab0 mRNA were observed in areas of the brain that are heavily myelinated. Rab0 mRNA was also detected in othe r tissues such as kidney, liver, skeletal muscle. These data provide i nitial evidence regarding signal transduction pathways that regulate i ntracellular transport in oligodendrocytes. (C) 1997 Elsevier Science B.V.