Foxg1 and Emx2 control of cortico-cerebral astrogenesis and Emx2 as a novel tool to suppress glioblastoma multiforme

Cortico--‐cerebral astrogenesis is a tightly regulated process. Astrocytic outputs mainly depend on two factors: progression of multipotent precursors towards the astroglial lineage and sizing of the astrogenic proliferating pool. Uncontrolled proliferation of astroglial cells in adult may give rise to severe pathologies, such as glioblastoma multiforme (GBM), for which no cure is presently available. The aim of this study was to study the role of two transcription factors, Foxg1 and Emx2, in the regulation of mouse corticocerebral astrogenesis and to employ Emx2 as a possible therapeutical tool to counteract GBM. We addressed this issue by combined gain-and loss--of--‐function methods, in vivo as well as in primary cultures of cortico—cerebral precursors and of patients’ GBM cell lines. We found that Foxg1antagonizes the commitment of early neural stem cells toward glial fate, while Emx2 suppress the proliferation of astrocyte—committed progenitors. We showed that Foxg1 inhibits the transcription of the well-‐known glial gene Gfap, possibly by impacting the regulation of the gliogenic transactive pathways. Then, we found that Emx2 overexpression in cortico--‐cerebral stem cells shrunk the proliferating astrogenic pool, resulting in a severe reduction of the astroglial outcome. We showed that this was caused by EgfR and Fgf9 downregulation and that both phenomena originated from exaggerated Bmp signaling and Sox2 repression. Furthermore, we provided evidence that in vivo temporal progression of Emx2 levels in cortico--‐cerebral multipotent precursors contributes to confine the bulk of astrogenesis to postnatal life. Finally, we translated our findings on Emx2 role in the normal astrogenesis to a possible gene therapy to suppress glioblastoma multiforme tumor. As for this last part of the study, we investigated the impact of Emx2 overexpression on patient malignant cells in vitro as well as upon transplantation into mouse recipient brains. We discovered that Emx2 overexpression induced the collapse of seven out of seven in vitro tested glioblastoma cell lines. Moreover, it suppressed four out of four of these lines in vivo in short--‐term approaches and it also increased the survival of GBM--‐transplanted mice in a long--‐term experiment. As proven by dedicated rescue assays, the anti--‐oncogenic activity of Emx2 originated from its impact on at least six metabolic nodes, which accounts for the robustness of its effect. Finally, in two out of two tested lines, the tumor culture collapse was also achieved when Emx2 was driven by a neural stem cell--‐specific promoter, likely active within tumor--‐initiating cells. All that points to Emx2 as a novel, promising tool for therapy of glioblastoma and prevention of its recurrencies.