Identification of Sox17 as a transcription factor that regulates oligodendrocyte development

Microarray analysis of oligodendrocyte lineage cells purified by fluorescence-activated cell sorting (FACS) from 2′,3′-cyclic nucleotide 3′-phosphodiesterase (CNP)-enhanced green fluorescent protein (EGFP) transgenic mice revealed Sox17 (SRY-box containing gene 17) gene expression to be coordinately regulated with that of four myelin genes during postnatal development. In CNP-EGFP-positive (CNP-EGFP⁺) cells, Sox17 mRNA and protein levels transiently increased between postnatal days 2 and 15, with white matter O4⁺ preoligodendrocytes expressing greater Sox17 levels than Nkx2.2⁺ (NK2 transcription factor related, locus 2) NG2⁺, or GalC⁺ (galactocerebroside) cells. In spinal cord, Sox17 protein expression was undetectable in the primary motor neuron domain between embryonic days 12.5 and 15.5 but was evident in Nkx2.2⁺ and CC1⁺ cells. In cultured oligodendrocyte progenitor cells (OPCs), Sox17 levels were maximal in O4⁺ cells and peaked during the phenotypic conversion from bipolar to multipolar. Parallel increases in Sox17 and p27 occurred before MBP protein expression, and Sox17 upregulation was prevented by conditions inhibiting differentiation. Sox17 downregulation with small interfering RNAs increased OPC proliferation and decreased lineage progression after mitogen withdrawal, whereas Sox17 overexpression in the presence of mitogen had opposite effects. Sox17 overexpression enhanced myelin gene expression in OPCs and directly stimulated MBP gene promoter activity. These findings support important roles for Sox17 in controlling both oligodendrocyte progenitor cell cycle exit and differentiation.