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First published online 30 August 2006
doi: 10.1242/dev.02560

Development 133, 3895-3905 (2006)
Published by The Company of Biologists 2006
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N-cadherin is required for the polarized cell behaviors that drive neurulation in the zebrafish

Elim Hong and Rachel Brewster*

Department of Biological Sciences, University of Maryland Baltimore County, Baltimore, MD 21250, USA.


Figure 1
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  		Fig. 1. Analysis of cell behaviors in wild-type embryos. (A-H) Cross sections through the anterior neuroepithelium of mGFP (green) and DAPI (blue) labeled embryos. Dorsal is towards the top in all panels; developmental stages are indicated in the upper right corner. C is a composite of multiple focal planes. All other panels are single frames. The insets in C and D are higher magnifications of the boxed in areas. s, superficial cells; d, deep cells; lat, lateral region; med, medial region. Double arrowheads indicate the angular orientation of cells, the dotted red line in C indicates the midline of the neural keel and the dotted white line in D outlines the neural keel. Scale bar: 20 µm.

 

Figure 2
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  		Fig. 2. The neural plate is multi-layered. Cross sections through the anterior lateral neural plate at the tailbud-1 som stage; dorsal is towards the top. (A) TEM micrograph, in which superficial cells are pseudocolored in blue, deep cells in red and the EVL in green. (B) Embryo double labeled with {alpha}-ß-cat (red) and {alpha}-Sox3C (green). (C) Embryo double labeled with {alpha}-ß-cat (red) and {alpha}-PH3 (green). Abbreviations are as in Fig. 1. Scale bars: in A, 5 µm; in B, 20 µm for B,C.

 

Figure 3
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  		Fig. 3. Time-lapse imaging of wild-type cells. (A,B) Selected frames from time-lapse confocal movies are shown for a deep (A) and two superficial (B) cells. Time elapsed (in minutes) from the first frame is indicated in the upper right corner. mGFP-labeled embryos were imaged in the hindbrain region, from a dorsal view, beginning at approximately 2-3 som and extending through 6-7 som. Dotted red lines indicate the midline of the neural keel/rod, white lines mark the edges of the neural keel/tube, arrows and numbers indicate individual cells identified in multiple frames, asterisks in A indicate two daughter cells derived from a recent cell division, and the box in B' shows interdigitation of cells at the midline. Scale bar: 100 µm.

 

Figure 4
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  		Fig. 4. Analysis of junctional marker expression during neurulation. (A-P) Cross sections through the anterior neuroepithelium of wild-type (A,C,E,G,I,K,M,O), N-cad MO-injected (B,P) and N-cadp79emcf mutant (D,F,H,J,L,N) embryos. Developmental stages are indicated in the upper right corner; dorsal is towards the top in all panels. Embryos were labeled with {alpha}-ß-cat (A-J), {alpha}-ZO-1 (K,L), {alpha}-aPKC (M,N), DAPI (A-N) and Alexa-488-phalloidin (O,P). Insets in A-D show higher magnifications of cells. Asterisk in I indicates the position of the forming ventricle, arrowheads point to midline apical labeling, arrows in N point to apical {alpha}-aPKC labeling, arrows in P show rosettes, and the dotted line in P indicates apical localization of phalloidin. Scale bar: 20 µm.

 

Figure 5
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  		Fig. 5. Neural tube morphogenesis is blocked at the neural keel stage in N-cad mutants. (A-D) Dorsal view of embryos labeled by in situ hybridization with a dlx3 riboprobe. Anterior is to the left; developmental stages are indicated in the upper right corner. (A,B) Representative embryos from a cross between two N-cadp79emcf heterozygote parents. (C) Wild-type sibling; (D) N-cadp79emcf mutant. Double arrowheads indicate the width of the dorsal neural rod.

 

Figure 6
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  		Fig. 6. Analysis of cell behaviors in N-cad-depleted embryos. (A-H) Cross sections through the anterior neuroepithelium of mGFP and DAPI-labeled MO-injected (A,C,E,G,H) and mutant (B,D,F) embryos. Dorsal is towards the top in all panels; developmental stages are indicated in the upper right corner. C,D and E are composites of multiple focal planes. All other panels are single frames. The insets in F-H are images of wild-type embryos at comparable stages. Abbreviations and symbols are as in Fig. 1. Scale bar: 20 µm.

 

Figure 7
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  		Fig. 7. Time-lapse imaging of N-cad-depleted cells. (A,B) Selected frames from time-lapse confocal movies are shown for deep (A) and superficial (B) cells. Time elapsed (in minutes) from the first frame is indicated in the upper right corner. mGFP-labeled embryos were imaged in the hindbrain region, from a dorsal view, beginning at approximately 2-3 som and extending through 6-7 som. Symbols are as in Fig. 4. Scale bar: 100 µm.

 

Figure 8
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  		Fig. 8. The protrusive activity in N-cad-depleted embryos is unstable. (A,B) Single frames from time-lapse imaging are shown for wild-type (A) and N-cad-depleted (B) superficial cells. Time elapsed (in minutes) from the first frame is indicated in the upper right corner. mGFP-labeled embryos were imaged from a dorsal view, beginning at approximately the 3 som stage and extending through 4-5 som. Asterisks indicate individual cells identified in multiple frames; double arrowheads indicate the orientation of the mediolateral (ML) axis. Scale bar in A: 10 µm.

 

Figure 9
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  		Fig. 9. Model for neurulation in wild-type and N-cad embryos. (A,B) Models for neurulation in wild type (A) and N-cad mutants (B). Superficial cells are in dark yellow, deep cells in light yellow and the EVL is in blue. The dotted red line reveals the midline of the neural keel/rod; green dots represent junctional complexes.

 

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© The Company of Biologists Ltd 2006