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Endfoot regeneration restricts radial glial state and prevents translocation into the outer subventricular zone in early mammalian brain development

Abstract

Neural stem cells, called radial glia, maintain epithelial structure during the early neocortical development. The prevailing view claims that when radial glia first proliferate, their symmetric divisions require strict spindle orientation; its perturbation causes precocious neurogenesis and apoptosis. Here, we show that despite this conventional view, radial glia at the proliferative stage undergo normal symmetric divisions by regenerating an apical endfoot even if it is lost by oblique divisions. We found that the Notch–R-Ras–integrin β1 pathway promotes the regeneration of endfeet, whose leading edge bears ectopic adherens junctions and the Par-polarity complex. However, this regeneration ability gradually declines during the subsequent neurogenic stage and hence oblique divisions induce basal translocation of radial glia to form the outer subventricular zone, a hallmark of the development of the convoluted brain. Our study reveals that endfoot regeneration is a temporally changing cryptic property, which controls the radial glial state and its shift is essential for mammalian brain size expansion.

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Fig. 1: LGN knockout causes spindle misorientation and loss of the apical endfoot.
Fig. 2: Spindle misorientation does not impair RG at the proliferative stage.
Fig. 3: RG missing the apical endfoot extend a new process with ectopic adherens junctions.
Fig. 4: Radial glia regenerate the apical endfoot at the early neurogenic stage.
Fig. 5: Regeneration of the apical endfoot depends on the Notch, R-Ras and integrin β1 pathways.
Fig. 6: FRET analysis of R-Ras activity.
Fig. 7: Activation of Notch signalling inhibits oRG generation.
Fig. 8: Apical-endfoot regeneration restricts the timing of oRG generation.

Data availability

Source data are available online for Figs. 18, Extended Data Figs. 1,2,59 and Supplementary Fig. 1. Additional time-lapse movies that support the key findings of this study have been deposited in Figshare (https://figshare.com/projects/Endfoot_Regeneration/71684). All other data supporting the findings of this study are available from the corresponding author on reasonable request.

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Acknowledgements

We thank M. Lin and M. Matsuda for plasmids; T. Miyata, A. Kawaguchi, Y. Tsunekawa and Q. Wu for their technical advice; and M. Takeichi, S. Yonemura and S. Hayashi for critical discussion of the data. Some of the imaging experiments were performed at the RIKEN Kobe Light Microscopy Facility. TEM analysis was supported by the Laboratory for Ultrastructural Research at RIKEN BDR. This work was supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT)/Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research (KAKENHI) grant nos 18H04003, 17H05779 and 24113006 to F.M.; grant nos 16K21627 and 18K14828 to I.F. and grant no. 16K18381 to A.S. In addition, I.F. was a recipient of the RIKEN Special Postdoctoral Researcher Program.

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Contributions

I.F., A.S. and F.M. designed the project. I.F., F.K. and A.S. engaged in and performed all of the experiments. I.F. and F.K. observed the regeneration of RG. A.S. observed the effects of R-Ras and integrin β1. I.F. and T.S. performed the electron-microscopy analyses. T.S., I.F. and A.S. performed the ferret experiments. D.K., T.A. and G.S. generated the LGN-null mutant. D.K., F.K., T.S., I.F. and A.O. analysed the LGN-mutant phenotype in the fixed sections. S.M. and A.S. performed the Notch/NICD experiments. K.K. created the program for calculating spindle orientation. I.F and F.M. wrote the manuscript with input from all authors.

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Correspondence to Fumio Matsuzaki.

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Extended data

Extended Data Fig. 1 Generation of the LGN-null mutant mouse line and analysis of mitosis.

a, Schematic representation of the strategies for the generation of LGN-null mutant mice. The generation of the LGN-∆C allele was previously described16. See Methods for details. The directions of genotyping primers are indicated by arrows. b, A typical result of genotyping PCR for the LGN-null allele using Primers 1–3. Four independent littermates showed similar results, of which unprocessed gel images are indicated in Source data. c, Offspring from LGN-null heterozygous parents. The ratio of genotypes showed no inconsistency with the Mendelian ratio. Two-tailed χ2 test, P = 0.79. d, Cumulative plots of spindle orientations in the WT, LGN-heterozygous and the LGN-homozygous mutants at E11.5, E13.5, and E15.5. The data set is the same as Fig. 1b and n is indicated in Fig. 1b. The uniformly random orientation model is shown with dotted lines. Transparent bands, 95% confidence intervals by Wilson score interval. e, Time-lapse imaging of EGFP-Plekha7 mice at E12.5. Embryos were electroporated with an expression vector for CyRFP at E11.5. Arrows, a mitotic RG and its daughter cells. Arrowheads, the apical endfeet of the cells. A mitotic RG was distinguished from interphase cells by transient expansion of the apical membrane due to mitotic swelling and weakening of the EGFP-Plekha7 signal (10 and 20 min); the weakened signal of EGFP-Plekha7 at mitosis reflects the release of Plekha7 from the adherens junction into the cytoplasm at mitosis in the RG. The cell body split in two at 20 min, followed by apical adhesion belt splitting up to 50 min. Two biologically independent samples showed similar results. Scale bar, 5 µm.

Source data

Extended Data Fig. 2 Analysis of the LGN-mutant phenotypes.

a, Dot plots and box plots of the spindle orientations in WT and LGN-homozygous mutant dorsal cortices at E10.5 (n = 47 and 51 cells, respectively), E11.5 (n = 58 and 62), and E14.5 (n = 95 and 87). Two-tailed Kolmogorov–Smirnov test, P = 5.9 × 10−6 (E10.5), 4.3 × 10–14 (E12.5) and 4.7 × 10–9 (E14.5). b, Cumulative plots of a, as shown in Extended Data Fig. 1d. c, “Non-apical” mitotic RG (Pax6+, Tbr2 and PH3+ cells) residing at a distance of > 30 µm from the ventricular surface but remains in the VZ (arrows) in the LGN mutant dorsal cortex at E14.5. The dotted line indicates the VZ margin. Scale bar, 100 µm. Similar results were observed in two biologically independent experiments. d, e, Percentages of apical and non-apical mitotic RG (Pax6+, Tbr2 and PH3+ cells) in WT (n = 6 embryos) and LGN-heterozygous (n = 13 embryos) mice at E14.5, as shown in Fig. 2d. Two-tailed Mann–Whitney U-test, p = 0.53. f, WT and LGN-homozygous mutant cortices at E10.5 and E12.5 stained with TUNEL, an anti-Pax6 antibody and DAPI. Scale bar, 100 µm. No induction of apoptotic cells was observed in the LGN mutant at either stage. Similar results were observed in two biologically independent experiments. g, h, mInsc overexpression modulates spindle orientations in RG. WT dorsal cortices were electroporated with the control or mInsc overexpression plasmid along with the EGFP marker plasmid at E11.5 and analysed at E12.5. EGFP+ cells at anaphase were analysed as described in Fig. 1b. g, Dot and box plots of the spindle orientation in the control (n = 63 cells from 6 embryos) and mInsc overexpression (n = 59 cells from 7 embryos). Box plots are defined as described in Fig. 1b. Two-tailed Kolmogorov–Smirnov test, P < 2.2 × 10–16. ***P < 0.001. h, Cumulative plot of (g). The uniformly random orientation model is shown with a dotted line. Transparent bands, 95% confidence intervals by Wilson score interval.

Source data

Extended Data Fig. 3 mInsc overexpression causes spindle misorientation, and a resultant off-apical cell extends a new apical process at the early neurogenic stage.

a, b, Time-lapse imaging of control (a) and mInsc-overexpressing (b) RG at E12.5. WT embryos were electroporated with the indicated plasmids at E11.5. The dorsal cortices were sliced at E12.5 and observed from a transverse view. White dotted lines indicate the ventricular surface. Each colour of arrowheads and asterisks indicates an identical apical process and a cell body of each daughter cell. a, In the control, most RG divisions split the apical endfoot into both daughters. 20 out of 20 cells showed similar results in three experiments. b, mInsc overexpression frequently caused bypassing divisions, which generated a basal daughter cell that lost the apical endfoot (yellow asterisk). In most cases of such bypassing divisions, the migrating basal daughter newly extended a process toward the apical endfoot (arrows). 10 out of 11 cells showed similar results in one experiment. c–f, WT dorsal cortices electroporated at E11.5 with plasmids for mInsc overexpression and sparse labelling with mem-EGFP were analysed at E12.5 by immunostaining for Sox2, Plekha7 and EGFP. In a pair of sister RG (Sox2+ and Tbr2, e, f), one sister cell shows an apical extension with Plekha7 accumulation (d, arrows). gm, WT dorsal cortices electroporated by the same condition as in (cf). Cell shapes visualized by mem-EGFP were analysed in every focal plane and overlaid with colours separately (pseudocolor in g, j, k). g, k, Projection images of 20-µm thick sections. hj, l, m, Single focal images. gj, Immunostaining for EGFP, ZO-1 and Pax6, showing a pair of Pax6+ cells (h, i), in which one sister cell (h) extended an apical process detaching from the ventricular surface and contacted the other sister cell at its apical tip, where ZO-1 accumulated (j). km, Immunostaining for EGFP, ZO-1 and Tbr2, showing a pair of Tbr2 and Tbr2+ cells that were assumed to be asymmetric neurogenic division products (l, m). The Tbr2 daughter cell exhibited ZO-1 accumulation at the tip of the apical extension, suggesting that the process with ZO-1 accumulation was derived from RG, but not from IP. Arrows, ZO-1 accumulation at the tips of apically extending processes. Asterisks, background staining of vascular endothelial cells. cm, Similar results were observed in at least two biologically independent samples. Scale bars, 10 µm (ai, km) and 2 µm (j).

Extended Data Fig. 4 Visualization of regenerating apical processes in LGN mutants with EGFP–Plekha7.

a, b, Two-photon imaging of dissected dorsal cortices from (a) LGN-heterozygous and (b) LGN-homozygous EGFP-Plekha7 mice at E10.5. Projection images of en face views and transverse views of the square regions with white dotted lines are shown. The yellow dotted lines indicate the basal edges of the tissues. Arrows, non-apical EGFP-Plekha7 foci. c, Immunostaining of LGN-homozygous EGFP-Plekha7 mice at E11.5 for EGFP, Plekha7 and β-catenin. Arrows, colocalization of EGFP and Plekha7 with β-catenin. Scale bar, 10 µm. d, Time-lapse imaging of EGFP-Plekha7 in the LGN-homozygous mutant at E11.5. Max projection images from en face and transverse views are shown. Arrows, a non-apical EGFP-Plekha7 focus; arrowhead, a newly emerged apical endfoot. e, Schematic image of the three-dimensional analysis of EGFP-Plekha7 foci. Images were taken from the apical side (en face view). The x- and y-axes are parallel to the apical surface, and the z-axis is parallel to the apico-basal axis of the tissue. Kymographs were generated by projecting signals in a defined volume, as indicated by the yellow box. See Methods for details. f, Kymographs and en face view of EGFP-Plekha7 during delamination in LGN-heterozygous or homozygous mice at E13.5. Delaminating apical endfeet were coloured by green. Only a faint EGFP-Plekha7 signal was observed during delamination (arrowheads), which occurred most likely due to cell differentiation. Each data was obtained from at least two biologically independent samples with similar results. Scale bars, 50 µm (a, b), 10 µm (ce), and 5 µm (f).

Extended Data Fig. 5 Quantification of adhesion plaques in the LGN mutant and WT.

a, Schematic illustration of the analysis of EGFP-Plekha7 foci in the LGN mutant. The dynamics of each individual focus were analysed by using three-dimensional positions every 10 minutes. b, c, Trajectories and angles of EGFP-Plekha7 foci in the LGN mutant at E11.5. b, Trajectories were analysed along the z-axis as depicted in (a). c, Angles were analysed for every 10 minutes. 90 and –90 degrees represent movements toward the apical and basal sides of a tissue, respectively. n = 128 displacements in 10 min of 8 plaques from 2 embryos. d, e, Trajectories and angles of EGFP-Plekha7 foci in the LGN mutant at E13.5. Note that E13.5 data were obtained every 5 minutes but the analysis in (e) was performed every 10 minutes. n = 146 displacements in 10 min of 9 plaques from 2 embryos. Two-tailed Kolmogorov–Smirnov test comparing (c) and (e), P = 9.7×10–13. f, Extension of the apical process at E14.5 under mInsc overexpression. WT dorsal cortices were electroporated with the indicated plasmids at E13.5 and analysed from transverse view at E14.5. Left, a kymograph of EGFP-ZO-1. Right, images of a bypassing division (1 h 40 min) and its progenies (green and blue asterisks) at the indicated time points. The arrowheads indicate adhesion plaques. The arrow indicates weak signal of a delaminating endfoot (as shown in Extended Data Fig. 4f). The descending rate of the apical process at E14.5 was approximately 0.2-fold of that in E11.5 (compare with Fig. 4b). Two independent experiments showed similar results. g, h, Inheritance (g) and origin (h) of the apical endfeet in the WT background at E11.5, E13.5, and E15.5. Data from 4 (E11.5), 4 (E13.5), and 5 (E15.5) embryos. g, n = 620 (E11.5), 465 (E13.5), and 360 (E15.5) cells. h, n = 1,323 (E11.5), 857 (E13.5), and 960 (E15.5) cells. h, Two-tailed Fisher's exact test between E11.5 and E13.5 or E15.5, P = 5.5×10–3 or 4.9×10–4, respectively. *P < 0.05, **P < 0.01. Error bars, 95% confidence intervals.

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Extended Data Fig. 6 Regeneration of the apical endfoot in the LGE.

af, Immunostaining of LGE (a, b, e, f) and MGE (c, d) in WT (e), LGN-heterozygous (a, c) or LGN-homozygous (b, d, f) mutants for PH3, Sox2 and Ascl1, at E11.5 (ad) and E14.5 (e, f). Arrows indicates Sox2+ Ascl1 PH3+ cells outside the VZ. Scale bars, 100 µm. g, Kymographs of EGFP-Plekha7 in the E11.5 LGE of LGN-heterozygous and LGN-homozygous mutants. Arrowheads indicate adhesion plaques moving away from the apical surface. Scale Bar, 10 µm. h, i, Inheritance (h) and origin (i) of the apical endfeet in the LGE of LGN-heterozygous and LGN-homozygous mutants at E11.5 and E14.5. Analyses were performed over 13.5 h (E11.5) or 24 h (E14.5). Data of LGN-heterozygous and LGN-homozygous mutants were obtained respectively from 2 and 3 (E11.5), or 1 and 3 (E14.5) embryos. Sample sizes of LGN-heterozygous and LGN-homozygous are respectively, 263 and 409 cells (h, E11.5); 124 and 192 cells (h, E14.5); 528 and 731 cells (i, E11.5); 412 and 1,215 cells (i, E14.5). Two-tailed Fisher's exact test, h, P < 2.2×10–16 (E11.5) and P = 2.8×10–6 (E14.5); i, p = 1×10–6 (E11.5) and 1 (E14.5), respectively. ***P < 0.001; n.s., P ≥ 0.05.

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Extended Data Fig. 7 Regeneration of the apical endfoot in the thalamus.

a, Immunostaining of the developing thalamus in LGN-heterozygous or LGN-homozygous mutants for PH3, Sox2 and Ascl1 at E11.5. Scale bar, 100 µm. Two independent experiments showed the similar results. b, c, Inheritance (b) and origin (c) of apical endfeet in the thalamus of LGN-heterozygous and LGN-homozygous mutants at E11.5. Analyses were performed over 13.5 h. b, n = 226 (LGN-heterozygous) and 161 (LGN-homozygous) cells from 2 and 3 embryos, respectively. c, n = 252 (LGN-heterozygous) and 417 (LGN-homozygous) cells from 2 and 3 embryos, respectively. Two-tailed Fisher's exact test, b, P < 1×10–15, c, P = 9.4×10–7. ***P < 0.001.

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Extended Data Fig. 8 Effects of NICD overexpression, integrin β1 knockdown and R-Ras knockout on apical-endfoot regeneration.

a, FACS analysis of dorsal cortical cells using pHes1-d2EGFP mice. EGFP+ fraction was defined according to the range outside the WT cell distribution (left). The EGFP+ fraction was separated into EGFP-high and EGFP-low populations based on the peak of the E11.5 distribution. Percentages of EGFP high and low populations are indicated. n = 92,009 (WT, E11.5), 92,155 (pHes1-d2EGFP, E11.5), 94,721 (E13.5), 90,876 (E14.5) and 89,649 (E15.5) cells from 7, 6, 7, 8, and 6 embryos, respectively. ****P <0.0001. Fisher's exact test comparing with E11.5, P < 2.2×10–16. b, Time-lapse imaging of a cell expressing mInsc and NICD at E14.5 from en face and transverse views. Arrows, the tip of an extending process, which finally formed an adhesion belt of EGFP-ZO-1 at the apical surface of the tissue (at 6 h 00 min). Two independent experiments showed similar results. c, Ratio of Pax6 and Pax6+ cells inside or outside the VZ among all EGFP+ cells in the control, mInsc overexpression, NICD expression, and expression of both. The same data set as in Fig. 7a, b. Data are mean ± s.d. of embryos. dd’’, Immunostaining for Rab11 (magenta) and ZO-1 (green) in an LGN-homozygous mutant mouse at E11.5. Rab11 accumulated adjacent to ZO-1 ectopic foci (d’) and the apical adhesion belt (d’’). Two independent experiments showed similar results. Scale bars, 5 µm. e, f, Origin (g) and inheritance (h) of the apical endfeet in Itgb1 knockdown under mInsc overexpression at E14.5. Data from 5 embryos each. e, n = 452 (control) and 628 (Itgb1 knockdown) cells. f, n = 249 (control) and 347 (Itgb1 knockdown) cells. Two-tailed Fisher's exact test, P = 0.18. n.s., P ≥ 0.05.

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Extended Data Fig. 9 FRET analysis of the R-Ras activity.

a, b, The R-Ras activity in the dorsal cortex and LGE. Each WT brain region was electroporated with R-Ras FRET probe at E13.5 and analysed at E14.5. Data are mean ± s.d. of n = 98 (dorsal cortex) and 71 (LGE) cells from one embryo each. Two-tailed Mann–Whitney U-test, P < 1×10–15. c, d, The R-Ras activity in the dorsal cortex under NICD expression. WT brains were electroporated with R-Ras FRET probe and the control or NICD expression plasmids at E13.5 and analysed at E14.5. Data are mean ± s.d. of n = 115 (control) and 166 (NICD expression) cells from two embryos each. Two-tailed Mann–Whitney U-test, P = 8.1×10–6. eh, Effects of Fgf10 in the endfoot regeneration. e, WT brains were electroporated with the control or Fgf10 overexpression plasmids at E11.5 and analysed by immunostaining for BLBP at E12.5. Similar results were observed in two biologically independent samples for each condition. f, g, Inheritance (f) and origin (g) of the apical endfeet in Fgf10 overexpression under mInsc overexpression at E12.5. Data from 6 embryos each. f, n = 170 (control) and 206 (Fgf10 overexpression). g, n = 213 (control) and 277 (Fgf10 overexpression). Two-tailed Fisher's exact test, P = 1. h, FRET analysis of the R-Ras activity under Fgf10 overexpression at E12.5. Data are mean ± s.d of n = 133 (control) and 138 (Fgf10 overexpression) cells from 2 embryos each. Two-tailed Mann–Whitney U-test, P = 0.75. *P < 0.05; ***P < 0.001; n.s., P ≥ 0.05. Scale bars, 10 µm (a, c) and 100 µm (e).

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Supplementary information

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Supplementary Video 1

Apical-endfoot dynamics in the LGN-heterozygous dorsal cortex at E11.5. The E11.5 LGN-heterozygous dorsal cortex was observed at 10-min intervals using EGFP-Plekha7. A z-projection movie of a 30 × 30 µm square region was shown. Two independent experiments showed similar results .

Supplementary Video 2

Apical-endfoot dynamics in the LGN-homozygous dorsal cortex at E11.5. The E11.5 LGN-homozygous dorsal cortex was observed at 10-min intervals using EGFP-Plekha7. A z-projection movie of a 30 × 30 µm square region was shown. Two independent experiments showed similar results .

Supplementary Video 3

Apical-endfoot dynamics in the WT background at E11.5. The E11.5 WT dorsal cortex was observed at 5-min intervals using EGFP-Plekha7. A z-projection and transverse projection movies of a 50.7 × 50.7 µm square region were shown at 5-min intervals. The arrow indicates an adhesion plaque that finally generated a new endfoot (2:50) in the right images. Drifting was adjusted as described in Methods. Four independent experiments showed similar results .

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Fujita, I., Shitamukai, A., Kusumoto, F. et al. Endfoot regeneration restricts radial glial state and prevents translocation into the outer subventricular zone in early mammalian brain development. Nat Cell Biol 22, 26–37 (2020). https://doi.org/10.1038/s41556-019-0436-9

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