Increased PO glycoprotein gene expression in primary and transfected rat Schwann cells after treatment with axolemma‐enriched fraction

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Abstract
To elucidate the role of axonal plasma membrane factors in the differentiation of Schwann cells, we investigated the effect of an axolemma-enriched fraction (AEF) isolated from myelinated CNS tissue on the expression of PO glycoprotein, the major glycoprotein in peripheral myelin, in primary rat Schwann cells (PSC) isolated from sciatic nerve, as well as in a transfected rat Schwann cell line (TSC). AEF increased PO-mRNA levels in PSC and TSC in a concentration-dependent manner, producing a maximal induction of nearly twofold after 48 hr of treatment. A similar induction of PO mRNA was elicited in TSC by the cAMP-activating agents 8-bromo-cAMP and forskolin, which have been shown to induce myelin proteins in PSC. In addition to inducing PO mRNA, AEF and forskolin also increased the amount of PO protein in TSC, as indicated by increased PO-immunoreactive staining. However, in TSC, axolemma caused no increase in expression of CAT linked to a PO promoter while forskolin caused a marked increase in the expression from the PO promoter. These results suggest that AEF, in contrast to forskolin, does not regulate PO-mRNA expression at the level of transcriptional activity. These in vitro systems may be useful for the study of axolemmal factors that in-duce Schwann cell differentiation.

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