Postnatal tamoxifen-induced inactivation of SREBP cleavage-activating protein (SCAP) in astrocytes interferes with full myelin membrane synthesis.

<p><b>A)</b> Expression analysis of recombination-reporter protein td-Tomato (tdT, red) in astrocytes (glial fibrillary acidic protein [GFAP], green), oligodendrocytes (Olig2, green), or neurons (NeuN, green) in the corpus callosum of Glast-CreERT2-tdT-SCAP animals (P56) treated with tamoxifen at P15–P17. Arrowheads denote cells that show coexpression of tdT with cell-type specific markers (scale bar, 25 μm). <b>B)</b> Expression of fatty acid synthase (FASN, in green) in astrocytes in tamoxifen-treated control (ctrl, with GFAP in red) or SCAP mutant mice (Mut). Astrocytes are visible by GFAP staining (red, for ctrl mice) or tdT expression (red, Mut). Arrowheads denote FASN+ astrocytes, asterisks denote FASN+ cells that are negative for GFAP or tdT (scale bar, 25 μm). Bar graph shows the number of FASN-positive astrocytes in WT (GFAP⁺FASN⁺ cells) and GFAP-SCAP mice (tdT⁺FASN⁺ cells) or FASN-positive non-astrocyte cells (GFAP^-FASN⁺ or tdT^-FASN⁺ cells). The values are provided as a percentage of the total number of cells expressing GFAP, tdT, or FASN. Data are presented as mean ± SEM. *** = <i>p</i> < 0.001 using <i>t</i> test, <i>n</i> = 3. <b>C)</b> Electron microscopy (EM) analysis of corpus callosum myelination in cross-sections of either tamoxifen-treated control (ctrl) or SCAP mutant mice (Mut) at P56. The relation between axon diameter (x) and g-ratio (y) was y = 0.1308x + 0.6872 for Ctrl and y = 0.1022x + 0.7408 for Mut, with coefficients of determination R² = 0.32986 (Ctrl) and R² = 0.29418 (Mut). <b>D)</b> Bar graph shows the percentage of axons that are myelinated. <b>E)</b> Morphometric analysis of axons on optic nerves of Ctrl and SCAP mutant mice showing g-ratio per class of axonal diameter for myelinated axons, and <b>F)</b> axonal size distribution for both myelinated and nonmyelinated axons. <i>t</i> test * = <i>p</i> < 0.05. ** = <i>p</i> < 0.01, <i>n</i> = 3. The numeric data underlying Fig 7B and C can be found in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002605#pbio.1002605.s006" target="_blank">S1 Data</a>.