Promyelinating Schwann Cells Express Tst-1/SCIP/Oct-6

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Abstract
Tst-1/SCIP/Oct-6, a POU domain transcription factor, is transiently expressed by developing Schwann cells and is required for their normal development into a myelinating phenotype. Intst-1/scip/oct-6–null sciatic nerves, Schwann cells are transiently arrested at the “promyelinating” stage, when they have a one-to-one relationship with an axon but before they have elaborated a myelin sheath. To determine when Schwann cells express Tst-1/SCIP/Oct-6, we examined β-galactosidase (β-gal) expression in heterozygous tst-1/scip/oct-6 mice, in which one copy of the tst-1/scip/oct-6 gene has been replaced with the LacZ gene. β-Gal expression from the LacZ gene seems to parallel Tst-1/SCIP/Oct-6 expression from the endogenoustst-1/scip/oct-6 gene in developing and regenerating sciatic nerves. Furthermore, electron microscopic examination of 5bromo-4-chloro-3-indolyl-β-d-galactopyranoside– (X-gal) and halogenated indolyl-β-d-galactoside– (Bluo-gal) stained nerves showed that promyelinating Schwann cells express the highest levels of β-gal, both in developing and in regenerating nerves. Thus, the expression of β-gal, a surrogate marker of Tst-1/SCIP/Oct-6, peaks at the same stage of Schwann cell development at which development is arrested intst-1/scip/oct-6–null mice, indicating that Tst-1/SCIP/Oct-6 has a critical role in promyelinating Schwann cells.