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Adherens junction-dependent and -independent steps in the establishment of epithelial cell polarity in Drosophila.

Harris TJ, Peifer M - J. Cell Biol. (2004)

Bottom Line: We found apical accumulation of both Drosophila E-Cadherin (DE-Cad) and the apical cue Bazooka (Baz) as cells first form.Some epithelial structures are retained, however.These structures maintain apical Baz, accumulate apical Crumbs, and organize polarized cytoskeletons, but display abnormal cell morphology and fail to segregate the basolateral cue Discs large from the apical domain.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.

ABSTRACT
Adherens junctions (AJs) are thought to be key landmarks for establishing epithelial cell polarity, but the origin of epithelial polarity in Drosophila remains unclear. Thus, we examined epithelial polarity establishment during early Drosophila development. We found apical accumulation of both Drosophila E-Cadherin (DE-Cad) and the apical cue Bazooka (Baz) as cells first form. Mutant analyses revealed that apical Baz accumulations can be established in the absence of AJs, whereas assembly of apical DE-Cad complexes requires Baz. Thus, Baz acts upstream of AJs during epithelial polarity establishment. During gastrulation the absence of AJs results in widespread cell dissociation and depolarization. Some epithelial structures are retained, however. These structures maintain apical Baz, accumulate apical Crumbs, and organize polarized cytoskeletons, but display abnormal cell morphology and fail to segregate the basolateral cue Discs large from the apical domain. Thus, although epithelial polarity develops in the absence of AJs, AJs play specific roles in maintaining epithelial architecture and segregating basolateral cues.

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Cytoskeletal polarity in armm/z mutant epithelia. (A–C) WT cross sections, stage 9. (A) Actin (green) accumulates near apical Baz (red). (B) Centrosomes (γ-tubulin; green) are between nuclei and apical Baz (red). (C) MTs (green) form an apical basket. (D–L) Early armm/z folds (D, E, G, H, J, and K) and later rosettes (F, I, and L). (D–F, arrowheads) Actin (green) colocalizes with apical Baz (red). (F, arrows) Dissociated cells have nonpolarized cortical actin. (G–I, arrowheads) Centrosomes (green) are between nuclei and apical Baz (red). (J–L, arrowheads) MTs (green) are enriched near Baz (red). (M) WT epithelium, stage 9. Apical MT meshwork. (N) Sub-apical section. Lateral MT bundles in cross section (N, arrowhead). (O–Q) Dissociated armm/z cells. Apical and sub-apical sections. Note nonpolarized MT networks. Bars, 5 μm.
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fig8: Cytoskeletal polarity in armm/z mutant epithelia. (A–C) WT cross sections, stage 9. (A) Actin (green) accumulates near apical Baz (red). (B) Centrosomes (γ-tubulin; green) are between nuclei and apical Baz (red). (C) MTs (green) form an apical basket. (D–L) Early armm/z folds (D, E, G, H, J, and K) and later rosettes (F, I, and L). (D–F, arrowheads) Actin (green) colocalizes with apical Baz (red). (F, arrows) Dissociated cells have nonpolarized cortical actin. (G–I, arrowheads) Centrosomes (green) are between nuclei and apical Baz (red). (J–L, arrowheads) MTs (green) are enriched near Baz (red). (M) WT epithelium, stage 9. Apical MT meshwork. (N) Sub-apical section. Lateral MT bundles in cross section (N, arrowhead). (O–Q) Dissociated armm/z cells. Apical and sub-apical sections. Note nonpolarized MT networks. Bars, 5 μm.

Mentions: WT epithelia also have cytoskeletal polarity. Actin is enriched around the apical cortex (Fig. 8 A), where it binds AJs via α-cat and is in close proximity to Baz (Fig. 8 A). Centrosomes localize above the nuclei (Fig. 8 B), whereas MTs form an apical meshwork (Fig. 8 M) and run down the lateral membrane (Fig. 8, C and N, arrowhead). To assess the role of AJs in organizing cytoskeletal polarity we examined armm/z mutants.


Adherens junction-dependent and -independent steps in the establishment of epithelial cell polarity in Drosophila.

Harris TJ, Peifer M - J. Cell Biol. (2004)

Cytoskeletal polarity in armm/z mutant epithelia. (A–C) WT cross sections, stage 9. (A) Actin (green) accumulates near apical Baz (red). (B) Centrosomes (γ-tubulin; green) are between nuclei and apical Baz (red). (C) MTs (green) form an apical basket. (D–L) Early armm/z folds (D, E, G, H, J, and K) and later rosettes (F, I, and L). (D–F, arrowheads) Actin (green) colocalizes with apical Baz (red). (F, arrows) Dissociated cells have nonpolarized cortical actin. (G–I, arrowheads) Centrosomes (green) are between nuclei and apical Baz (red). (J–L, arrowheads) MTs (green) are enriched near Baz (red). (M) WT epithelium, stage 9. Apical MT meshwork. (N) Sub-apical section. Lateral MT bundles in cross section (N, arrowhead). (O–Q) Dissociated armm/z cells. Apical and sub-apical sections. Note nonpolarized MT networks. Bars, 5 μm.
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Related In: Results  -  Collection

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fig8: Cytoskeletal polarity in armm/z mutant epithelia. (A–C) WT cross sections, stage 9. (A) Actin (green) accumulates near apical Baz (red). (B) Centrosomes (γ-tubulin; green) are between nuclei and apical Baz (red). (C) MTs (green) form an apical basket. (D–L) Early armm/z folds (D, E, G, H, J, and K) and later rosettes (F, I, and L). (D–F, arrowheads) Actin (green) colocalizes with apical Baz (red). (F, arrows) Dissociated cells have nonpolarized cortical actin. (G–I, arrowheads) Centrosomes (green) are between nuclei and apical Baz (red). (J–L, arrowheads) MTs (green) are enriched near Baz (red). (M) WT epithelium, stage 9. Apical MT meshwork. (N) Sub-apical section. Lateral MT bundles in cross section (N, arrowhead). (O–Q) Dissociated armm/z cells. Apical and sub-apical sections. Note nonpolarized MT networks. Bars, 5 μm.
Mentions: WT epithelia also have cytoskeletal polarity. Actin is enriched around the apical cortex (Fig. 8 A), where it binds AJs via α-cat and is in close proximity to Baz (Fig. 8 A). Centrosomes localize above the nuclei (Fig. 8 B), whereas MTs form an apical meshwork (Fig. 8 M) and run down the lateral membrane (Fig. 8, C and N, arrowhead). To assess the role of AJs in organizing cytoskeletal polarity we examined armm/z mutants.

Bottom Line: We found apical accumulation of both Drosophila E-Cadherin (DE-Cad) and the apical cue Bazooka (Baz) as cells first form.Some epithelial structures are retained, however.These structures maintain apical Baz, accumulate apical Crumbs, and organize polarized cytoskeletons, but display abnormal cell morphology and fail to segregate the basolateral cue Discs large from the apical domain.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.

ABSTRACT
Adherens junctions (AJs) are thought to be key landmarks for establishing epithelial cell polarity, but the origin of epithelial polarity in Drosophila remains unclear. Thus, we examined epithelial polarity establishment during early Drosophila development. We found apical accumulation of both Drosophila E-Cadherin (DE-Cad) and the apical cue Bazooka (Baz) as cells first form. Mutant analyses revealed that apical Baz accumulations can be established in the absence of AJs, whereas assembly of apical DE-Cad complexes requires Baz. Thus, Baz acts upstream of AJs during epithelial polarity establishment. During gastrulation the absence of AJs results in widespread cell dissociation and depolarization. Some epithelial structures are retained, however. These structures maintain apical Baz, accumulate apical Crumbs, and organize polarized cytoskeletons, but display abnormal cell morphology and fail to segregate the basolateral cue Discs large from the apical domain. Thus, although epithelial polarity develops in the absence of AJs, AJs play specific roles in maintaining epithelial architecture and segregating basolateral cues.

Show MeSH
Related in: MedlinePlus