Additional supporting information available online.

STEM_00119_sm_suppfig1.tif6168KSupporting Information Figure 1. NG2 and PDGFRα expression after the 7-day EGF infusions. Upon the growth factor infusions a higher expression of NG2 (A - B) and PDGFRα (C - D) is found around of the lateral ventricles and dorsal SVZ as compared to saline-infused controls. The EM picture shows an EIP (see text) process close to a blood vessel (BV), but do not contact the endotelium (E). Inset shows a higher magnification of the squared area. Ribosomes (r), mitochondria (m), 1 = endothelial cell cytoplasm, 2 = basal lamina, 3 = astrocyte process and 4 = EIP process. V: Ventricle. Scale bar in A – D = 20 μm; E = 2 μm.
STEM_00119_sm_suppfig2.tif4208KSupporting Information Figure 2. EGF infusion does not activated parenchymal astrocytes. EGF was infused in the lateral ventricle and RCAS-GFP was injected in different brain regions (see methods). A: The 7-day EGF infusion induces an over-expression of Olig2 around the ventricle, but the progeny of RCAS-labeled astrocytes remains close to the needle track (arrowheads). Similar findings were found in corpus callosum (B) and cortex (C). No GFP+ cells were found when virus was injected onto brain surface. Sep: Septum, Str: Striatum. V: Ventricle. Scale bar = 200 μm.
STEM_00119_sm_suppfig3.tif18273KSupporting Information Figure 3. EIPs' differentiation in the gray matter upon EGF pump removal. The table shows the quantification of several markers in brain parenchyma. In the saline-infused animals a limited number of SVZ-derived are incorporated into brain parenchyma as compared to EGF-infused mice. Asterisks indicate differences statistically significant (P < 0.05; Student “t” test). A - C: GFP+ cell co-expressing GFAP/S100β. D: Pre-embedding immunogold EM of a highly branched GFP+ cell that has a number of intermediate filaments (arrowheads). Insets: Top left, the same cell under the light microscope; top right, semi-thin section of the GFP+ cell; bottom right, intermediate filaments and silver-enhanced precipitates. E: A subset of GFP+ cells showed few ramifications, non-bushy morphology and expressed NG2. Scale bars: C and E = 10 μm; D = 2 μm; inset = 0.5 μm.
STEM_00119_sm_suppfig4.tif4912KSupporting Information Figure 4. Ectopic migration chains. Upon EGF pump removal, several ectopic chains of migrating neuroblast are commonly found in the brain parenchyma. Arrows show doublecortin+ (A) and PSA-NCAM+ cell chains (B) in septum (Sep). Nuclei are counterstained with DAPI (blue). CC: Corpus callosum; Str: Striatum; dSVZ: Dorsal subventricular zone. Scale bars = 20 μm.
STEM_00119_sm_suppfig5.tif3455KSupporting Information Figure 5. Olig 2 expression after a vehicle or EGF infusion onto brain surface. As found for intraventricular EGF infusions (figure 1 of this report), many Olig2+ cells are observed around the SVZ in animals infused with EGF on the surface of the brain. This was not observed in mice that received vehicle onto the brain surface. Nuclei are counterstained with DAPI (blue). CC: Corpus callosum; Str: Striatum; V: Ventricle. Scale bar = 20 μm.

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