QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

First published online 4 July 2007
doi: 10.1242/dev.02869

This Article Summary Full Text Full Text (PDF) Supplementary Material Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Métin, C. Articles by Molnár, Z. Search for Related Content PubMed PubMed Citation Articles by Métin, C. Articles by Molnár, Z.

Conserved pattern of tangential neuronal migration during forebrain development

Christine Métin^1,2,3,, Chantal Alvarez^1,2, David Moudoux⁴, Tania Vitalis^1,2,*, Claude Pieau⁵ and Zoltán Molnár⁴

¹ INSERM, U839, Institut du Fer à Moulin, 17 rue du Fer à Moulin, 75005 Paris, France.
² Université Pierre et Marie Curie-Paris6, UMR-S839, 75005 Paris, France.
³ CNRS UMR 8542, Equipe Régionalisation Nerveuse, Niveau 8, Ecole Normale Supérieure 46, rue d'Ulm, 75230 Paris Cedex 05, France.
⁴ Department of Physiology, Anatomy and Genetics, Le Gros Clark Building, University of Oxford, South Parks Road, Oxford OX1 3QX, UK.
⁵ Institut Jacques Monod, UMR 7592, CNRS et Université Pierre et Marie Curie-Paris6 and Paris7, 75251 Paris, France.

View larger version (88K): [in this window] [in a new window]   Fig. 1. Distribution of GABA and Nkx2.1 immunoreactivity in the developing turtle telencephalon. (A-C) Detection of GABA in coronal sections of embryonic turtle brains from the level close to the optic chiasm region. At stage 14 (A), cells above the VZ of the pallium are GABA immunonegative. By contrast, the VZ of the subpallium shows an intense neuropil labeling and the mantle contains darkly stained cells. At stage 16 (B), tangentially oriented GABA-immunoreactive cells are present throughout the entire pallium with the exception of the dorsal-most sector. (Inset) Enlarged view showing neurites ending with large growth cones (white arrows). By this stage, the density of GABA-positive cells is increased in the VZ of the dorsal and medial ridges (the LGE and MGE, respectively) of the subpallium, which are separated by a slight depression (dashed line). At stage 19 (C), GABA-immunopositive cells distribute more medially in the dorsal pallium. A clear transition in GABA staining occurs at the pallial-subpallial boundary dorsal to the sulcus between the enlarged DVR and LGE (arrowhead). GABA-positive cells still concentrate in the VZ of the LGE. (D-F) Detection of Nkx2.1 in coronal sections of embryonic turtle brains using fluorescent secondary antibodies. The depression or groove (dashed line) separating the LGE and MGE correlates well with the dorsal limit of Nkx2.1 expression in the subpallial VZ (white arrow). Nkx2.1-positive cells distribute in the mantle of the MGE from stage 14 (D), in the mantle of the LGE at stage 17 (E), and in the striatum, DVR and LC at stage 20 (F). (Inset) Enlarged view showing sparse immunopositive cells in the DC. DC, dorsal cortex; DVR, dorsal ventricular ridge; LC, lateral cortex; LGE, lateral ganglionic eminence; m, mantle; MGE, medial ganglionic eminence; P, pallium; SP, subpallium; Str, striatum; VZ, ventricular zone. Scale bars: 500 µm.

View larger version (100K): [in this window] [in a new window]   Fig. 2. Regionalized expression of Nkx2.1, Tbr1, Pax6 and Darpp-32 in the telencephalon of turtle embryos. Nkx2.1 (A-C,M), Tbr1 (D-F,K), Pax6 (G-I) and Darpp-32 (J,L). (A-I) Coronal sections of stage 14 turtle embryos at three distinct rostrocaudal levels. (J-M) Stage 16 (J,K) and stage 18 (L,M) coronal sections. (J,L) Darpp-32-immunoreactive cells form a compact region in the embryonic striatum (mantle zone of the LGE) and distribute under the pia in the presumptive lateral cortex (arrows in L). Scale bars: 500 µm. (N) Drawings of the rostrocaudal series of thick (200-300 µm) coronal sections of a stage 16 turtle telencephalon showing limits of the presumptive MGE, LGE, LC and DVR (LC/DVR) and DC. The Darpp-32-positive area is indicated in gray.

View larger version (92K): [in this window] [in a new window]   Fig. 3. CMFDA tracer injections into the subpallium and pallial-subpallial boundary (PSB) label cells in the pallium. (A-D'') Four coronal slices from stage 15 turtle embryos were labeled from the VZ of the PSB (A), LGE (B) or MGE (C, rostral and D, caudal) with CMFDA-coated bamboo fibers (black or white stars), cultured for 5 days, fixed in PAF and immunoreacted with Darpp-32 antibodies (A',B',C',D'). (A'',B'',C'',D'') Merged images (CMDFA, green; Darpp-32, red). (A) A PSB injection ventral to the DVR and dorsal to the Darpp-32-positive LGE area (A') labeled cells in the DVR and LC but not in the DC. (B) Tracer placement into the LGE labeled numerous cells oriented radially in the Darpp-32-positive area (B') and few cells in the pallium. (C,D) MGE injections ventral to the Darpp-32-positive area (C',D') labeled cells between the Darpp-32-positive LGE and DVR, in the LC and along the VZ of the DVR (C'',D''). A few labeled cells are present in the DC. Scale bar: 200 µm. (E-H') Four coronal slices from turtle embryos at stage 17 (E-G') or 19 (H,H') were labeled with CMDFA-coated bamboo fibers (black or white stars) placed into the VZ of the PSB (E,H), LGE (F) or MGE (G) and stained for Darpp-32 (E'-G') or calbindin (H') immunoreactivity after fixation. PSB placements labeled a very large number of cells in the PSB (E,H), and labeled scattered cells in the DVR and cortex (LC, DC). LGE placements at stage 17 (F) labeled numerous cells in the pallium, at the PSB and along the pallial VZ. By contrast, MGE placements (G) no longer labeled cells in the pallium, and labeled few cells along the PSB. Scale bars: 200 µm in E-G'; 500 µm in H,H'.

View larger version (39K): [in this window] [in a new window]   Fig. 4. Summary of migration patterns from different sectors in embryonic turtle forebrain at various stages. CMDFA placement sites are represented by a color code (see A). In labeled and cultured slices, the density of labeled cells was evaluated in sectors (as defined in B). The dotted line in the DVR, LGE and MGE separates the VZ and postmitotic areas that were analyzed separately. Gray and striped areas show the location of Darpp-32-positive cells in the LGE and the lateral cortex, respectively. Each scheme summarizes the mean distribution of labeled cells as observed in a number (n) of slices labeled from the same area at same stage. Injection sites are arranged into rows and stages are arranged in columns with the stages indicated at the bottom. The analysis was semi-quantitative: in each sector of each injected slice, the number of labeled cells was evaluated as: +++, high; ++, medium; +, low; (+), half that of low. The mean number of labeled cells in each area was multiplied by two and translated into a color code proportional to the cell density (see text).

View larger version (62K): [in this window] [in a new window]   Fig. 5. Morphology and migration properties of cells released from the PSB or MGE explants in culture. (A-G) Cell migration and axonal outgrowth from stage 14 (A), 16 (B) and 18 (C) telencephalic turtle explants cultured on a laminin substrate. Explants prepared from the DC, DVR, PSB, LGE or MGE were cultured for 2 days and stained for GABA or ß-tubulin (TuJ1). Large numbers of GABAergic neurons migrated from MGE explants at stage 14 and 16, and from LGE explants at stage 18. PSB explants released a significant number of cells from stage 14 to 18. Cells around the DVR and cortical explants were always few in number. Long and dense axons were only observed around pallial explants. At high magnification, cells released from PSB (D) explants show longer neurites and larger somas than cells released from MGE (E) explants, which show large growth cones. (F) Summary of semi-quantitative analysis of the cell migration and axonal outgrowth (by the method explained in Fig. 4 legend). At least six explants of the same origin were analyzed at each stage. (G) Diagrams showing lateral views of stage 16 and 18 hemispheres summarizing the origin of explants that released migrating cells in vitro. Regions in dark gray released high cell densities, those in light gray released few cells. As development proceeds, LGE and PSB explants produce more cells, whereas this capacity decreased in the MGE. (H-I'') CMFDA placement (asterisk) in the PSB (H) of a stage 16 slice labeled cells with thick leading neurites and frequent bifurcations (H', arrows). Placement in the MGE (I) of a stage 16 slice labeled densely packed cells that showed simpler and thinner neurites (I'). GABA immunostaining (red in H'',I'') revealed numerous processes and cell bodies in slices. In optical sections obtained with confocal microscopy at the surface of each slice (H'',I''), a significant proportion of cells labeled from the PSB or MGE with CMFDA are GABA-immunopositive (arrowheads). Scale bars: 50 µm in C,D,H-I''; 100 µm in E.

View larger version (51K): [in this window] [in a new window]   Fig. 6. Mouse-turtle interspecies grafting experiments reveal conserved guidance mechanisms in mammals and reptiles. (A-B') When DiI-labeled explants of PSB and MGE of stage 16 to 18 turtle embryos were grafted into E13.5 mouse forebrain slices, the released labeled cells (red) migrated within the host tissue. Cells from PSB explants grafted into the corticostriatal boundary (A) migrated along the corticostriatal boundary and accumulated ventrally (arrow), whereas MGE cells grafted into the basal telencephalon (B,B') migrated in the orthogonal direction, across the corticostriatal boundary. Turtle MGE cells dispersed and migrated as individuals to colonize the mouse cortex (B') and some developed branched neurites in the host tissue (B''). (C-F) GFP-expressing MGE explants from E12.5 mouse embryos grafted into stage 16 turtle slices (C) or into stage 17 telencephalic vesicles in ovo (D) were no longer visible after a few days. Individual GFP-positive mouse MGE cells migrated long distances within the telencephalon of turtle embryos, colonized the entire slice (C), or the pallium in the in ovo experiments (D). By contrast, cortical explants (E,F) still formed a compact mass of tissue several days after grafting and released very few cells. The few cells that were released did not migrate very far, either in grafted slice (E) or grafted hemisphere (F). Scale bars: 500 µm in A,B,C-F; 200 µm in B'; 40 µm in B''.