EXPRESSION OF THE PROTEOLIPID PROTEIN GENE IN GLIAL-CELLS OF THE POSTNATAL PERIPHERAL NERVOUS-SYSTEM OF RODENTS

The proteolipid protein (PLP) gene encodes for two proteins, PLP and D M-20, which are produced by alternative splicing of exon 3B. PLP is th e major CNS myelin protein and is postulated to play a structural role at the intraperiod line. Its developmental expression mirrors that of CNS myelination. DM-20 predominates in the embryo and prior to myelin ation of the CNS and may be involved in glial cell development. The PL P gene is expressed in the PNS in which DM-20 is the predominant isofo rm at all ages, In this study we describe the localization of the two isoforms in the post-natal rodent PNS using immunostaining and reverse transcriptase PCR. DM-20 is present in relatively high abundance in n on-myelin-forming Schwann cells and within cytoplasmic regions of myel inated internodes, particularly the paranodes and Schmidt-Lanterman in cisures and also the outer Schwann cytoplasm and perinuclear cytoplasm . DM-20 is also located in the perineuronal satellite cells of spinal, cranial and autonomic ganglia and in the ensheathing cells of the olf actory nerve layer of the olfactory bulb. PLP was detected by immunocy tochemistry in the perinuclear region of myelinated internodes; PCR an alysis indicated small amounts of PLP mRNA in the other locations but protein was not detected by immunostaining. Neither protein was identi fied in compact myelin of the PNS. DM-20 is the predominant product of the PLP gene expressed in a wide variety of peripheral glia. Its pres ence is not correlated to a myelin-forming state. Other studies have d emonstrated early embryonic expression of the PLP gene throughout the PNS and all these features support the hypothesis that any putative ro le for DM-20 is unrelated to myelination but may involve glial cell de velopment.