A,B: Illustration of the migration of grafted NSPCs along the cingulum (in green) and BrdU-labeled cells (in red) that migrated from the SVZ. C,D and H,I: SVZ-derived BrdU-labeled cells migrate along the RMS and are recruited in the CC (arrows) of mice grafted with control (C,H) or Reelin-secreting cells (D,I). E: Quantification of SVZ-derived BrdU-labeled cells recruited in the corpus callosum 7 days after NSPC graft in the cingulum. F,G: Illustration of HEK cells secreting Reelin grafted in the ventricle. J: Quantification of SVZ-derived cells recruited in the CC 7 days after HEK cell graft in the ventricle. Reelin increases the recruitment of SVZ-derived cells toward CC independently of the location of the Reelin source (in the corpus callosum (A–E) or in the ventricle (F–J)). CC: corpus callosum; Cx: cortex; s: striatum. V: ventricle. Scale bars  = 50 µm.

Reelin triggers cell detachment from the chains of migrating progenitors and increases migration speed. A: Schematic diagram of SVZ explant cultures in the presence or absence of a focal source of Reelin. Aggregates of HEK cells stably expressing Reelin (or DsRed for controls) were placed in close proximity to SVZ explants. The length of chains formed by cells migrating out of the explants was measured in 3 independent points proximally and distally to the HEK aggregate. B: Quantification of individual cells detached from the chains. C–F: Migration pattern in the absence (C,D) and presence (E,F) of Reelin. D, F: Magnification of white rectangle in C and E respectively. A large number of isolated cells migrating outside the chains can be seen in the presence of Reelin. G: Chain length proximal and distal to HEK aggregates producing Reelin. No difference can be observed between proximal and distal chain length, thereby arguing against a chemoattractant effect of Reelin. H: Chain length in Reelin versus DsRed conditions, showing a significant lengthening in the presence of Reelin. I,J: video time-lapse recording of individual migrating cells in the absence (I) or presence (J) of Reelin, with trajectory colored (blue to red along 9 h). K: Quantification of migration speed (average of more than 200 cells from 3 independent experiments). Scale bar in C,E  = 100 µm; in D,F,I,J  = 50 µm.

A, B: BrdU labeling evidencing SVZ-derived NSPCs migrating in the RMS and recruited toward the demyelination lesion delineated by white doted line, in wild-type (C) and Dab1−/− mice (D). C, D: Quantification of BrdU-positive SVZ-derived cells within the lesion site showing a significant decrease in cell recruitment in mice lacking the Dab1 adaptor required for Reelin signaling (C) as well as in Wt mice treated with Reelin blocking antibody CR50 (D). Scale bars: 50 µm.

A–B: Western blot and semi-quantitative analysis of Reelin expression in peri-lesional areas 1 to 3 days (D1, D2, D3) after unilateral cortical ischemia (A) or demyelination (B). Reelin expression was normalized to α-tubulin and expressed in percentage of contralateral (unlesioned) side (from 5 or 6 mice). Western blot illustrations in A and B are representative of Reelin expression on day 3. C, D: In situ hybridization (C) and Reelin immunolabeling (D) in the cortex 3 days after lesion revealing higher number of labeled cells in the ipsilateral cortex. E: Cell immunoreactivity is maximal in close proximity to the lesion. The asterisk (*) indicates the core of the thermocoagulation lesion site. F: Reelin-positive cells (green) colocalize with NeuN (red) and GABA-positive (light blue) interneurons in the cortex after demyelination lesion. G: Quantification of Reelin expressing cells (in situ hybridization) and of labeling intensity (immunolabeling) in cortex contralateral or proximal to a thermocoagulation lesion. contra: areas from contralateral side to the lesion; ipsi: areas proximal to the lesion; LPC: lysolecithine demyelinating lesion. Scale bars: C = 100 µm; D = 50 µm; E = 25 µm; F = 10 µm.

The overall RMS structure was revealed by DCX immunofluorescence, and individual cell migration in the RMS was analyzed after graft of GFP+ SVZ cells into the SVZ-RMS corner. A,B: Schematic representation of the graft of GFP+ SVZ cells (in green) in the SVZ/RMS of Wt (A) and transgenic mice overexpressing Reelin (B) (Reelin expression is schematized in yellow). C–G: Migrating neuroblasts (DCX+, in red) in the RMS of Wt (C,E) and TgRln (D,F,G) mice. E and F are enlarged views of the white squares in C and D respectively. Note the disorganization of the RMS in transgenic mice, with interruptions in the RMS (between arrows in D), and neuroblasts escaping the RMS in chains (F) or individually (G) and showing misoriented processes and a complex morphology. H,I: GFP+ SVZ grafted cells (in green) integrate and migrate in the RMS (DCX in red) of control (H) and TgRln (I) mice. J,K: GFP+ SVZ cells reached the olfactory bulb 7 days after grafting in Wt (J) as in TgRln (K) mice. L–O: GFP+ grafted cells remain confined to the RMS in Wt mice (L,N) whereas they tend to be misoriented (arrowheads) or even leave the RMS (arrows) in TgRln mice (M,O). P: Quantification of the proportion of grafted cells that were misoriented (presenting an angle superior to 45° with RMS orientation) or that detached and left the RMS. CC: corpus callosum; ob: olfactory bulb; s: striatum; TgRln: transgenic mice overexpressing Reelin; Wt: Wild-type mice. Scale bars : C, D = 100 µm; E,F,G,L,M  = 50 µm; H,I,N,O  = 20 µm; J,K  = 10 µm.

A: Illustration of lysolecithin-induced demyelination in the corpus callosum. The demyelination lesion is revealed by myelin basic protein (MBP) immunostaining. B: Schematic representation of demyelination lesion induction in the corpus callosum of TgRln mice overexpressing Reelin (yellow) in forebrain structures. C, D: BrdU labeling evidencing SVZ-derived NSPCs migrating in the RMS and recruited toward the demyelination lesion delineated by white doted line, in Wt (C) and TgRln (D) mice. E: Quantification of BrdU+ SVZ-derived cells within the lesion site showing a highly significant increase in cell recruitment in transgenic mice overexpressing Reelin as compared to their Wt littermates. F: Phenotype of SVZ-derived progenitors recruited at the lesion site 7 days after LPC injection. Recruited cells mostly give rise to astrocytes (GFAP-positive) and to cells of the oligodendrocyte lineage (Olig2-positive). Among BrdU/Olig2 labeled cells, a subpopulation also expresses CC1, a marker of mature oligodendrocytes (represented by lighter gray at the upper part of the columns). Only a negligible proportion of recruited cells adopt neuronal fate. Reelin overexpression does not seem to have major impact on the fate of recruited cells. G: Double labeling for BrdU (red) and GFAP (green) in the lesion site. H: Triple labeling for BrdU (red), Olig2 (white) and CC1 (green) in the lesion site. Arrows indicate BrdU-Olig2 co-labeled cells; arrowhead indicates one BrdU-positive cell also labeled with Olig2 and CC1. Small white squares (in G and H) are enlarged at the right side of the picture to show the co-labeling. TgRln: transgenic mice overexpressing Reelin; Wt: Wt mice. Scale bars  = 100 µm.