Context-dependent Regulation of Notch Signaling in Glial Development and Tumorigenesis [Bulk RNA-seq]

In the mammalian brain, Notch signaling maintains the cortical stem cell pool and regulates the glial cell fate choice and differentiation. However, the function of Notch in regulating glial development and its involvement in tumorigenesis have not been well understood. Here, we show that Notch inactivation by genetic deletion of Rbpj in stem cells decreases astrocytes but increases oligodendrocytes with altered internal states. Interestingly, inhibiting Notch in glial progenitors does not affect cell generation but instead accelerates the growth of Notch-deprived oligodendrocyte progenitor cells (OPCs), and OPC-related glioma. We also identified a crosstalk between oligodendrocytes and astrocytes, with premyelinating oligodendrocytes secreting Bmp4, which is repressed by Notch, to upregulate GFAP expression in adjacent astrocytes. Moreover, Notch inactivation in stem cells causes a glioma subtype shift from astroglia-associated to OPC-correlated patterns, and vice versa. Our study reveals Notch's context-dependent function, promoting astrocytes and astroglia-associated glioma in stem cells and repressing OPCs and related glioma in glial progenitors. Bulk RNA-seq: Mice cortices were sorted and collected at P2 from both control (Olig2-Cre; H2B-GFPF/+) and Rbpj-cko (Olig2-Cre; RbpjF/F; H2B-GFPF/+) mice.在哺乳动物大脑中，Notch信号通路可维持皮层干细胞池的稳态，并调控神经胶质细胞的命运选择与分化过程。然而，Notch在调控胶质细胞发育中的功能，及其参与肿瘤发生的作用尚未被充分阐明。本研究发现，在干细胞中通过基因敲除Rbpj使Notch通路失活后，星形胶质细胞数量减少，而少突胶质细胞数量增加且其内部状态发生改变。有趣的是，在胶质祖细胞中抑制Notch通路并不会影响细胞生成，反而会加速Notch缺陷型少突胶质祖细胞（oligodendrocyte progenitor cells，OPCs）以及OPC相关胶质瘤的生长。我们还鉴定出少突胶质细胞与星形胶质细胞之间存在串扰：髓鞘形成前少突胶质细胞会分泌骨形态发生蛋白4（Bmp4），该因子的表达可被Notch通路抑制，进而上调邻近星形胶质细胞内的胶质纤维酸性蛋白（glial fibrillary acidic protein，GFAP）表达。此外，在干细胞中使Notch通路失活会导致胶质瘤亚型从星形胶质相关模式转向OPC相关模式，反之亦然。本研究揭示了Notch通路的功能具有细胞环境依赖性：在干细胞中，Notch通路可促进星形胶质细胞形成以及星形胶质相关胶质瘤，而在胶质祖细胞中则会抑制OPCs及其相关胶质瘤的发生。整体RNA测序（bulk RNA-seq）实验中，我们于小鼠出生后第2天（postnatal day 2，P2）分选收集对照组（Olig2-Cre; H2B-GFPF/+）与Rbpj条件性敲除小鼠（Olig2-Cre; RbpjF/F; H2B-GFPF/+）的大脑皮层组织。