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SMARCA4 loss and mutated β-catenin induce proliferative lesions in the murine embryonic cerebellum

ABSTRACT: Almost all medulloblastomas (MB) of the Wingless/Int-1 (WNT) subgroup are characterized by hotspot mutations in CTNNB1, and mouse models have convincingly demonstrated the tumor-initiating role of these mutations. Additional alterations in SMARCA4 are detected in around 20 % of WNT MB but their functional role is mostly unknown. We therefore amended previously described Blbp-cre::Ctnnb1(ex3)fl/wt mice by the introduction of a floxed Smarca4 allele. In contrast to existing literature, even mutated β-catenin on its own in our Blbp-cre::Ctnnb1(ex3)fl/wt mice induced severe developmental phenotypes including a thinned cerebral cortex, hydrocephalus, missing cerebellar layering, and non-proliferative cell accumulations in brain stem and cerebellum. An additional homozygous loss of SMARCA4 even resulted in prenatal death for most mice. Interestingly, Blbp-cre::Ctnnb1(ex3)fl/wt::Smarca4fl/fl mutants developed big proliferative lesions in the cerebellum that evolved from E13.5 to E16.5. Histological and molecular analysis of these lesions by DNA methylation analysis and single-cell RNA sequencing suggest an origin in early undifferentiated SOX2-positive cerebellar progenitors. Furthermore, upregulation of WNT signaling and altered actin/cytoskeleton organization and neuronal differentiation were evident in mutant cells. In vitro, cells harboring alterations in both Ctnnb1 and Smarca4 were negatively selected and did not show tumorigenic potential after transplantation in adult recipient mice. However, mutant cells displayed increased proliferation compared to controls in cerebellar explant culture, indicating an important role of the embryonic microenvironment in the development of lesions. Altogether, these results represent an important first step in unravelling tumorigenic mechanisms induced by aberrant WNT signaling and a SMARCA4 deficiency.

ORGANISM(S): Mus musculus

PROVIDER: GSE240627 | GEO | 2024/04/17

REPOSITORIES: GEO

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Project description:We examined the transformation susceptibility of different cerebellar stem/progenitors by developing several new Group3 medulloblastoma murine models using orthotopic transplantation and in utero electroporation (EP)-based in vivo gene transfer with Cre/LoxP-mediated conditional Myc gene activation and loss of Trp53 function. We used microarrays to compared the transcriptome of these novel Group3 medulloblastoma mouse models to existing mouse models of medulloblastoma subgroups and used cross-species analysis to compare these models to human medulloblastoma subgroups This study aimed to investigate the cell of origin of Group3 MB using our orthotopical MYC model followed by a novel electroporation approach. Orthotopic cell-lineage specific MYC tumors were generated by enforced Myc expression in P6 GNPs isolated from P0-1 tamoxifen treated [Atoh1-CreER;Trp53fl/-] and [Prom1-CreER;Trp53fl/-] mice followed by cortical implants in immunocompromised mice. These tumors are referred to as Atoh1ER-MYC [dka072-075], Prom1-CreER [dka077-081]. The first Group3 MB models in which tumors developed in situ were generated by electroporation of plasmids containing Myc and dominant negative Trp53 flanked by loxP sites into the fourth ventricle of E13.5 Blbp-Cre [dka081, 087, 089, 090, 091 and blm121], Gad2-IRES-Cre [blm128-130 and blm134] and Ptf1a-Cre [blm135-137] mouse embryos. The gene expression profile of these tumors were compared to our previously published Group3 MB model as well as SHH and WNT models of medulloblastoma. For SHH subgroup medulloblastoma, [dka001-005, 009, 033 and 034] and [dka050-057], spontaneous medulloblastomas from [Cdkn2c-/-; Trp53Fl/Fl; Nestin-Cre] and [Cdkn2c-/-; Ptch1+/-] (Uziel et al.,2005 Genes Dev) were used, respectively. For Group3 medulloblastomas, [dka013-16, 049 and 065-067], in which Myc was overexpressed in Cdkn2c-/-, Trp53-/- cerebellar cells and implanted into the cortices of immunocompromised nude mice prior to tumor isolation. For WNT subgroup medulloblastomas [pgr003, 016 and 066], spontaneously developed tumors from CTNNB1+/lox (ex3); BLBP-Cre; Trp53Fl/Fl (Gibson et al., 2010, Nature) were removed for RNA extraction.

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SMARCA4 loss and mutated β-catenin induce proliferative lesions in the murine embryonic cerebellum

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