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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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Polarity establishment during WT syncytial development and cellularization. (A) Schematic of syncytial nuclear division and (B–D) cellularization. Actin (orange), tubulin (blue). (A′–D′) Baz (red), DE-Cad (green), and Dlg (gray) in cross section (top) and from the embryo surface (bottom) during syncytial nuclear division (A′), and early (B′), mid (C′), and late cellularization (D′). Note intermixed distributions of Baz, DE-Cad, and Dlg along nuclear division and early cellularization furrows (A′ and B′, bracketed) and their early localization to apical microvilli (B′, blue arrowheads). At early to mid cellularization DE-cad is at basal junctions (B′and C′, blue arrows). During mid (C′) and late cellularization (D′) Baz and DE-Cad colocalize in apical accumulations (white arrows) that are likely spot junctions (arrowheads). Dlg shows nonspecific apical enrichment (D′). Bars, 5 μm.
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fig1: Polarity establishment during WT syncytial development and cellularization. (A) Schematic of syncytial nuclear division and (B–D) cellularization. Actin (orange), tubulin (blue). (A′–D′) Baz (red), DE-Cad (green), and Dlg (gray) in cross section (top) and from the embryo surface (bottom) during syncytial nuclear division (A′), and early (B′), mid (C′), and late cellularization (D′). Note intermixed distributions of Baz, DE-Cad, and Dlg along nuclear division and early cellularization furrows (A′ and B′, bracketed) and their early localization to apical microvilli (B′, blue arrowheads). At early to mid cellularization DE-cad is at basal junctions (B′and C′, blue arrows). During mid (C′) and late cellularization (D′) Baz and DE-Cad colocalize in apical accumulations (white arrows) that are likely spot junctions (arrowheads). Dlg shows nonspecific apical enrichment (D′). Bars, 5 μm.

Mentions: During syncytial nuclear divisions, we found that DE-Cad, Baz, and Dlg associate with pseudocleavage furrows (Fig. 1 A′). However, in cross section or embryo surface views, the three proteins only partially overlap and lack consistent colocalization (Fig. 1 A′, brackets). Thus, DE-Cad, Baz, and Dlg do not segregate to specific apical or basal domains during this stage.


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

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

Polarity establishment during WT syncytial development and cellularization. (A) Schematic of syncytial nuclear division and (B–D) cellularization. Actin (orange), tubulin (blue). (A′–D′) Baz (red), DE-Cad (green), and Dlg (gray) in cross section (top) and from the embryo surface (bottom) during syncytial nuclear division (A′), and early (B′), mid (C′), and late cellularization (D′). Note intermixed distributions of Baz, DE-Cad, and Dlg along nuclear division and early cellularization furrows (A′ and B′, bracketed) and their early localization to apical microvilli (B′, blue arrowheads). At early to mid cellularization DE-cad is at basal junctions (B′and C′, blue arrows). During mid (C′) and late cellularization (D′) Baz and DE-Cad colocalize in apical accumulations (white arrows) that are likely spot junctions (arrowheads). Dlg shows nonspecific apical enrichment (D′). Bars, 5 μm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172516&req=5

fig1: Polarity establishment during WT syncytial development and cellularization. (A) Schematic of syncytial nuclear division and (B–D) cellularization. Actin (orange), tubulin (blue). (A′–D′) Baz (red), DE-Cad (green), and Dlg (gray) in cross section (top) and from the embryo surface (bottom) during syncytial nuclear division (A′), and early (B′), mid (C′), and late cellularization (D′). Note intermixed distributions of Baz, DE-Cad, and Dlg along nuclear division and early cellularization furrows (A′ and B′, bracketed) and their early localization to apical microvilli (B′, blue arrowheads). At early to mid cellularization DE-cad is at basal junctions (B′and C′, blue arrows). During mid (C′) and late cellularization (D′) Baz and DE-Cad colocalize in apical accumulations (white arrows) that are likely spot junctions (arrowheads). Dlg shows nonspecific apical enrichment (D′). Bars, 5 μm.
Mentions: During syncytial nuclear divisions, we found that DE-Cad, Baz, and Dlg associate with pseudocleavage furrows (Fig. 1 A′). However, in cross section or embryo surface views, the three proteins only partially overlap and lack consistent colocalization (Fig. 1 A′, brackets). Thus, DE-Cad, Baz, and Dlg do not segregate to specific apical or basal domains during this stage.

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