Transcription factors ASCL1 and OLIG2 drive glioblastoma initiation and co-regulate tumor cell types and migration

Glioblastomas (GBMs) are highly aggressive, infiltrative, and heterogeneous brain tumors driven by complex genetic alterations. The basic-helix-loop-helix (bHLH) transcription factors ASCL1 and OLIG2 are dynamically co-expressed in GBMs; however, their combinatorial roles in regulating the plasticity and heterogeneity of GBM cells are unclear. Here, we show that induction of somatic mutations in subventricular zone (SVZ) progenitor cells leads to the dysregulation of ASCL1 and OLIG2, which then function redundantly and are required for brain tumor formation in a mouse model of GBM. Subsequently, the binding of ASCL1 and OLIG2 to each other's loci and to downstream target genes then determines the cell types and degree of migration of tumor cells. Single-cell RNA sequencing (scRNA-seq) reveals that a high level of ASCL1 is key in specifying highly migratory neural stem cell (NSC)/astrocyte-like tumor cell types, which are marked by upregulation of ribosomal protein, oxidative phosphorylation, cancer metastasis, and therapeutic resistance genes. Overall design: Fluorescently labeled tumors were induced in the brains of immunocompetent transgenic mice. Control tumors had endogenous expression of Ascl1 and experimental tumors overexpressed Ascl1 (Ascl1-OE). Tumor cells were isolated by fluorescence activated cell sorting (FACS) and then analyzed using scRNA-seq.

胶质母细胞瘤（Glioblastomas, GBMs）是一类侵袭性极强、兼具浸润性与异质性的脑肿瘤，其发生由复杂的遗传改变所驱动。碱性螺旋-环-螺旋转录因子（basic-helix-loop-helix, bHLH）家族的ASCL1与OLIG2在GBM中呈动态共表达，但二者在调控GBM细胞可塑性与异质性的协同作用仍不明确。本研究证实，在侧脑室下区（subventricular zone, SVZ）祖细胞中诱导体细胞突变，可导致ASCL1与OLIG2表达失调，二者随后发挥冗余功能，且在GBM小鼠模型中为脑肿瘤形成所必需。后续研究发现，ASCL1与OLIG2可结合彼此的基因位点及下游靶基因，进而决定肿瘤细胞的类型与迁移程度。单细胞RNA测序（single-cell RNA sequencing, scRNA-seq）分析显示，高水平ASCL1是确定高迁移性神经干细胞（neural stem cell, NSC）/星形胶质细胞样肿瘤细胞亚型的关键，该亚型以核糖体蛋白、氧化磷酸化、肿瘤转移及治疗抗性基因的上调为特征。整体实验设计：在免疫健全的转基因小鼠脑内诱导荧光标记的肿瘤，对照组肿瘤为内源表达Ascl1的肿瘤，实验组肿瘤为过表达Ascl1（Ascl1-OE）的肿瘤。通过荧光激活细胞分选（fluorescence activated cell sorting, FACS）分离肿瘤细胞，随后采用scRNA-seq进行分析。