Specialized cellular microenvironments, or ‘niches’, modulate stem cell properties, including cell number, self-renewal and fate decisions1,2. In the adult brain, niches that maintain a source of neural stem cells (NSCs) and neural progenitor cells (NPCs) are the subventricular zone (SVZ) of the lateral ventricle and the dentate gyrus of the hippocampus3,4,5. The size of the NSC population of the SVZ at any time is the result of several ongoing processes, including self-renewal, cell differentiation, and cell death. Maintaining the balance between NSCs and NPCs in the SVZ niche is critical to supply the brain with specific neural populations, both under normal conditions or after injury. A fundamental question relevant to both normal development and to cell-based repair strategies in the central nervous system is how the balance of different NSC and NPC populations is maintained in the niche. EGFR (epidermal growth factor receptor) and Notch signalling pathways have fundamental roles during development of multicellular organisms6. In Drosophila and in Caenorhabditis elegans these pathways may have either cooperative or antagonistic functions7,8,9. In the SVZ, Notch regulates NSC identity and self-renewal, whereas EGFR specifically affects NPC proliferation and migration10,11,12,13. This suggests that interplay of these two pathways may maintain the balance between NSC and NPC numbers. Here we show that functional cell–cell interaction between NPCs and NSCs through EGFR and Notch signalling has a crucial role in maintaining the balance between these cell populations in the SVZ. Enhanced EGFR signalling in vivo results in the expansion of the NPC pool, and reduces NSC number and self-renewal. This occurs through a non-cell-autonomous mechanism involving EGFR-mediated regulation of Notch signalling. Our findings define a novel interaction between EGFR and Notch pathways in the adult SVZ, and thus provide a mechanism for NSC and NPC pool maintenance.
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We thank N. Ratner for the Cnp–hEGFR mice. We are thankful to T. Hawley for technical advice in all FACS sorting experiments. We are grateful to J. Corbin and T. Haydar for critically reading this manuscript, and to all our colleagues at the Center for Neuroscience Research for discussion and support. We are thankful to N. Gaiano for discussion, for providing reagents and for his continuous advice on this project. We thank G. Corfas, A. Israel, C. L. Cepko, R. Kopan, R. Grosschedl, N. Gaiano and R. Kageyama for the gift of CBF-1, Hes1–GFP, Hes1-dsRED, Notch constructs, Dll–GFP, CBFRE–EGFP and Hes5–GFP, respectively. This work was supported by NIH R01NS045702 and R01NS056427 (V.G.), K99NS057944 (A.A.), ROO NS057944-03 (A.A.) and by NIH IDDRC P30HD40677 (V.G.). Electron microscopy was performed at the University of Connecticut, Department of Physiology and Neurobiology, with funding from NIH R01DC006881 to M.E.R., and from NSF DBI-0420580 for funds to purchase the Tecnai 12 Biotwin electron microscope.
The authors declare no competing financial interests.
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Aguirre, A., Rubio, M. & Gallo, V. Notch and EGFR pathway interaction regulates neural stem cell number and self-renewal. Nature 467, 323–327 (2010). https://doi.org/10.1038/nature09347