Department of Pediatric Hematology and Oncology, University Medical Center Hamburg-Eppendorf, Hamburg D-20251, Germany.
Research Institute Children's Cancer Center Hamburg, Hamburg D-20251, Germany.
J Neurosci. 2024 Apr 10;44(15):e1605232024. doi: 10.1523/JNEUROSCI.1605-23.2024.
Almost all medulloblastomas (MB) of the Wingless/Int-1 (WNT) type are characterized by hotspot mutations in , and mouse models have convincingly demonstrated the tumor-initiating role of these mutations. Additional alterations in are detected in ∼20% of WNT MB, but their functional role is mostly unknown. We, therefore, amended previously described brain lipid binding protein () mice by the introduction of floxed alleles. Unexpectedly, mutated and thereby stabilized β-catenin on its own induced severe developmental phenotypes in male and female mice in our hands, including a thinned cerebral cortex, hydrocephalus, missing cerebellar layering, and cell accumulations in the brainstem and cerebellum. An additional loss of SMARCA4 even resulted in prenatal death for most mice. Respective mutants (male and female) developed large proliferative lesions in the cerebellum evolving from E13.5 to E16.5. Histological and molecular analysis of these lesions by DNA methylation profiling and single-cell RNA sequencing suggested an origin in early undifferentiated SOX2-positive cerebellar progenitors. Furthermore, upregulated WNT signaling, altered actin/cytoskeleton organization, and reduced neuronal differentiation were evident in mutant cells. In vitro, cells harboring alterations in both and were negatively selected and did not show tumorigenic potential after transplantation in adult female recipient mice. However, in cerebellar explant cultures, mutant cells displayed significantly increased proliferation, suggesting an important role of the embryonic microenvironment in the development of lesions. Altogether, these results represent an important first step toward the unraveling of tumorigenic mechanisms induced by aberrant WNT signaling and SMARCA4 deficiency.
几乎所有的无翅型（Wingless/Int-1，WNT）型髓母细胞瘤（medulloblastoma，MB）的特征是存在热点突变，并且小鼠模型令人信服地证明了这些突变具有引发肿瘤的作用。在大约 20%的 WNT MB 中检测到 中的额外改变，但它们的功能作用大多未知。因此，我们通过引入 floxed 等位基因对先前描述的脑脂质结合蛋白（brain lipid binding protein，BLBP）小鼠进行了修饰。出乎意料的是，在我们手中，突变和由此稳定的 β-连环蛋白自身诱导雄性和雌性 小鼠出现严重的发育表型，包括大脑皮层变薄、脑积水、小脑分层缺失以及脑干和小脑中的细胞堆积。另外丧失 SMARCA4 甚至导致大多数小鼠产前死亡。相应的 突变体（雄性和雌性）在小脑中发展出大的增殖性病变，从 E13.5 到 E16.5 逐渐形成。通过 DNA 甲基化谱和单细胞 RNA 测序对这些病变进行的组织学和分子分析表明，其起源于早期未分化的 SOX2 阳性小脑祖细胞。此外，在突变细胞中可见上调的 WNT 信号、改变的肌动蛋白/细胞骨架组织以及减少的神经元分化。在体外，同时存在 和 改变的细胞被负选择，并且在成年雌性受体小鼠中移植后没有显示出肿瘤发生潜力。然而，在小脑外植体培养物中，突变细胞显示出明显增加的增殖，表明胚胎微环境在病变发展中具有重要作用。总的来说，这些结果代表了阐明异常 WNT 信号和 SMARCA4 缺失诱导的肿瘤发生机制的重要的第一步。
