Expression of the POU-domain transcription factors SCIP/Oct-6 and Brn-2 is associated with Schwann cell but not oligodendrocyte remyelination of the CNS

The class III POU-domain transcription factor SCIP/Oct-6 is expressed by promyelinating Schwann cells and, in tissue culture, by oligodendrocyte progenitors (OPs), but is down-regulated in both cells types as they differentiate. Although the expression of SCIP/Oct-6 has been examined in peripheral nerve remyelination, its expression in CNS remyelination has not been addressed. Using a toxin model of demyelination, in which the demyelinated axons are remyelinated in an age-dependent manner by both oligodendrocytes and Schwann cells, we have compared the expression of SCIP/Oct-6 mRNA with that of an OP marker (PDGF-αR), a marker of myelinating oligodendrocytes (PLP), and markers of myelinating Schwann cells (P₀ and Krox-20) by in situ hybridization. We have found that the expression of SCIP/Oct-6 mRNA precedes that of P₀ and Krox-20 mRNA expression, but bears little correlation with the expression profiles of either PDGF-αR or PLP mRNA. Moreover, there is a spatial correlation between the expression SCIP/Oct-6 mRNA and that of P₀ but not of PDGF-αR. These results indicate that SCIP/Oct-6 expression following CNS demyelination is associated with Schwann cell and not oligodendrocyte remyelination. We have also shown that another POU-domain transcription factor, Brn-2, is expressed during CNS remyelination, but that like SCIP/Oct-6, it too has an expression profile indicating that it is associated with the Schwann cell component of remyelination. In addition, we show that Brn-2 expression in Schwann cells is not restricted to CNS remyelination but is also expressed in a similar manner to SCIP/Oct-6 during Schwann cell myelination of neonatal peripheral nerves and regenerating transected adult nerve and in cultured Schwann cells following induction of elevated cAMP levels.