Fig 2: S100B expression in Olig2-null and Myrf conditional knockout mutants. a, b S100B+ cells were dramatically reduced in E18.5 Olig2-null spinal cord in the white matter, but not in the gray matter. c–j The number of S100B+/SOX10+ oligodendrocytes was significantly reduced in the white matter of spinal cord and forebrain (corpus callosum) in Myrf conditional knockout mutants. k–l Statistical analysis of the number of S100B+ oligodendrocytes in Olig2 and Myrf mutants. SOX10+/S100B+ cells are represented by white arrows. m Schematic diagram of the time window of S100B expression in differentiating oligodendrocytes and gray matter astrocytes. In oligodendrocyte lineage, S100B expression is slightly earlier than that of MYRF, and gradually down-regulated in ASPA+ mature oligodendrocytes. In astrocyte lineage, S100B is gradually up-regulated and maintained in adulthood. sc spinal cord, WM white matter, GM gray matter, CC corpus callosum, OLs oligodendrocytes, OPCs oligodendrocyte progenitor cells, RGCs radial glial cells. n = 3, *p < 0.05, **p < 0.01. Bar, 100 µm

Fig 3: The specificity of S100B antibodies. a–d Sections of P0 mouse spinal cord were subject to anti-S100B immunostaining. The mouse-anti-S100B monoclonal antibodies (green) and rabbit-anti-S100B polyclonal antibodies (red) marked the same population of cells. e, f In situ hybridization against S100b mRNA (f) displayed a nearly identical expression pattern to that of immunostaining (e). Bar, 100 µm

Fig 4: S100B is expressed in the differentiating oligodendrocytes. a–k Co-expression of S100B and SOX10 in mouse CNS tissues. Most S100B+ cells in spinal white matter and a few in the gray matter co-express SOX10 (arrows) (a–c). Similarly, nearly all the S100B+ cells are SOX10+ in the corpus callosum, and SOX10+/S100B+ cells are also presented in the cortex region (arrows) (d–k). White arrow heads refer to SOX10–/S100B+ astrocytes. l–o Co-expression of S100B and MYRF in mouse CNS tissues. Nearly all MYRF+ cells express S100B in P4 spinal white matter and P15 corpus callosum (arrows). p, q Co-expression of S100B and ASPA in brain corpus callosum. ASPA+ mature oligodendrocytes that have completely lost S100B expression are represented by blue arrow heads and ASPA–/S100B+ myelinating oligodendrocytes are indicated by white arrow heads. r–w Quantitative analyses of the co-expression of S100B with SOX10, MYRF and ASPA. sc spinal cord, WM white matter, GM gray matter, CC corpus callosum. n = 3, *p < 0.05, **p < 0.01. Bar, 100 µm

Fig 5: S100B is expressed in gray matter astrocytes but not white matter GFAP+ astrocytes. a–i Double labeling of S100B with ALDH1L1 and GFAP in the cortical region (a, c, e, h) and corpus callosum (b, d, f, g, i) of forebrain from P4 to adulthood. j–l Double labeling of S100B with ALDH1L1, GS and GFAP in P4 spinal cord. The arrow heads indicate the S100B+ astrocytes, and S100B+ cells that did not express astrocyte marker are indicated by white arrows. m, n Quantitative analysis of S100B expression in astrocytes. sc spinal cord, WM white matter, GM gray matter, CC corpus callosum. n = 3, *p < 0.05, **p < 0.01. Bar, 100 µm