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The positioning and segregation of apical cues during epithelial polarity establishment in Drosophila.

Harris TJ, Peifer M - J. Cell Biol. (2005)

Bottom Line: Adherens junctions (AJs) often direct this polarity, but we previously found that Bazooka (Baz) acts upstream of AJs as epithelial polarity is first established in Drosophila.Surprisingly, we found that Baz localizes to an apical domain below its typical binding partners atypical protein kinase C (aPKC) and partitioning defective (PAR)-6 as the Drosophila epithelium first forms.These results reveal key steps in the assembly of the apical domain in Drosophila.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA. tonyh@email.unc.edu

ABSTRACT
Cell polarity is critical for epithelial structure and function. Adherens junctions (AJs) often direct this polarity, but we previously found that Bazooka (Baz) acts upstream of AJs as epithelial polarity is first established in Drosophila. This prompted us to ask how Baz is positioned and how downstream polarity is elaborated. Surprisingly, we found that Baz localizes to an apical domain below its typical binding partners atypical protein kinase C (aPKC) and partitioning defective (PAR)-6 as the Drosophila epithelium first forms. In fact, Baz positioning is independent of aPKC and PAR-6 relying instead on cytoskeletal cues, including an apical scaffold and dynein-mediated basal-to-apical transport. AJ assembly is closely coupled to Baz positioning, whereas aPKC and PAR-6 are positioned separately. This forms a stratified apical domain with Baz and AJs localizing basal to aPKC and PAR-6, and we identify specific mechanisms that keep these proteins apart. These results reveal key steps in the assembly of the apical domain in Drosophila.

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Baz and AJs localize below aPKC and PAR-6 during WT epithelial development. (A) Early epithelial development (Dlg-stained embryos and schematics). At cellularization (left), membrane furrows separate each cell. At gastrulation (right), cells form the ectoderm and body compartments, e.g., the PMGI. (B) Cellularization. Baz (red) and DE-Cad (green) colocalize in apical puncta below the top of furrows (Dlg; blue). (C) Gastrulation. Baz (red) and DE-Cad (green) colocalize in apical puncta below the top of lateral membranes (Dlg; blue). (D and E) Cellularization. (D) aPKC (green) enriched above DE-Cad (red). (E) PAR-6 (green) cytoplasmic and along the entire furrow with slight enrichment above Baz (red). (F–H) Gastrulation. (F) aPKC (green) above DE-Cad (red). (G) PAR-6 (green) above Baz (red). (H) aPKC (green) and PAR-6 (blue) colocalize above Arm (red). (I and J) Stages 7 and 8 PMGI. (I) aPKC (green) and PAR-6 (blue) colocalize above Arm (red). (J) PAR-6 (green) above both Baz (red) and Arm (red, right). (K) Stage 14 gut. Baz (red) below PAR-6 (blue), but above Arm (green). (L) Segmental grooves, stage 14 epidermis. Baz (red) below PAR-6 (blue), but above Arm (green). Bars, 5 μm.
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fig1: Baz and AJs localize below aPKC and PAR-6 during WT epithelial development. (A) Early epithelial development (Dlg-stained embryos and schematics). At cellularization (left), membrane furrows separate each cell. At gastrulation (right), cells form the ectoderm and body compartments, e.g., the PMGI. (B) Cellularization. Baz (red) and DE-Cad (green) colocalize in apical puncta below the top of furrows (Dlg; blue). (C) Gastrulation. Baz (red) and DE-Cad (green) colocalize in apical puncta below the top of lateral membranes (Dlg; blue). (D and E) Cellularization. (D) aPKC (green) enriched above DE-Cad (red). (E) PAR-6 (green) cytoplasmic and along the entire furrow with slight enrichment above Baz (red). (F–H) Gastrulation. (F) aPKC (green) above DE-Cad (red). (G) PAR-6 (green) above Baz (red). (H) aPKC (green) and PAR-6 (blue) colocalize above Arm (red). (I and J) Stages 7 and 8 PMGI. (I) aPKC (green) and PAR-6 (blue) colocalize above Arm (red). (J) PAR-6 (green) above both Baz (red) and Arm (red, right). (K) Stage 14 gut. Baz (red) below PAR-6 (blue), but above Arm (green). (L) Segmental grooves, stage 14 epidermis. Baz (red) below PAR-6 (blue), but above Arm (green). Bars, 5 μm.

Mentions: We examined epithelial polarity as it is first established during Drosophila cellularization. Drosophila development begins in a syncytium. After 13 nuclear divisions, furrows form synchronously from the overlying plasma membrane compartmentalizing ∼6,000 nuclei into individual columnar cells (Nelson, 2003; see Fig. 1 A). Cellularization thus forms the first embryonic epithelium, which is then remodeled to drive gastrulation and further morphogenesis (see Fig. 1 A).


The positioning and segregation of apical cues during epithelial polarity establishment in Drosophila.

Harris TJ, Peifer M - J. Cell Biol. (2005)

Baz and AJs localize below aPKC and PAR-6 during WT epithelial development. (A) Early epithelial development (Dlg-stained embryos and schematics). At cellularization (left), membrane furrows separate each cell. At gastrulation (right), cells form the ectoderm and body compartments, e.g., the PMGI. (B) Cellularization. Baz (red) and DE-Cad (green) colocalize in apical puncta below the top of furrows (Dlg; blue). (C) Gastrulation. Baz (red) and DE-Cad (green) colocalize in apical puncta below the top of lateral membranes (Dlg; blue). (D and E) Cellularization. (D) aPKC (green) enriched above DE-Cad (red). (E) PAR-6 (green) cytoplasmic and along the entire furrow with slight enrichment above Baz (red). (F–H) Gastrulation. (F) aPKC (green) above DE-Cad (red). (G) PAR-6 (green) above Baz (red). (H) aPKC (green) and PAR-6 (blue) colocalize above Arm (red). (I and J) Stages 7 and 8 PMGI. (I) aPKC (green) and PAR-6 (blue) colocalize above Arm (red). (J) PAR-6 (green) above both Baz (red) and Arm (red, right). (K) Stage 14 gut. Baz (red) below PAR-6 (blue), but above Arm (green). (L) Segmental grooves, stage 14 epidermis. Baz (red) below PAR-6 (blue), but above Arm (green). Bars, 5 μm.
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fig1: Baz and AJs localize below aPKC and PAR-6 during WT epithelial development. (A) Early epithelial development (Dlg-stained embryos and schematics). At cellularization (left), membrane furrows separate each cell. At gastrulation (right), cells form the ectoderm and body compartments, e.g., the PMGI. (B) Cellularization. Baz (red) and DE-Cad (green) colocalize in apical puncta below the top of furrows (Dlg; blue). (C) Gastrulation. Baz (red) and DE-Cad (green) colocalize in apical puncta below the top of lateral membranes (Dlg; blue). (D and E) Cellularization. (D) aPKC (green) enriched above DE-Cad (red). (E) PAR-6 (green) cytoplasmic and along the entire furrow with slight enrichment above Baz (red). (F–H) Gastrulation. (F) aPKC (green) above DE-Cad (red). (G) PAR-6 (green) above Baz (red). (H) aPKC (green) and PAR-6 (blue) colocalize above Arm (red). (I and J) Stages 7 and 8 PMGI. (I) aPKC (green) and PAR-6 (blue) colocalize above Arm (red). (J) PAR-6 (green) above both Baz (red) and Arm (red, right). (K) Stage 14 gut. Baz (red) below PAR-6 (blue), but above Arm (green). (L) Segmental grooves, stage 14 epidermis. Baz (red) below PAR-6 (blue), but above Arm (green). Bars, 5 μm.
Mentions: We examined epithelial polarity as it is first established during Drosophila cellularization. Drosophila development begins in a syncytium. After 13 nuclear divisions, furrows form synchronously from the overlying plasma membrane compartmentalizing ∼6,000 nuclei into individual columnar cells (Nelson, 2003; see Fig. 1 A). Cellularization thus forms the first embryonic epithelium, which is then remodeled to drive gastrulation and further morphogenesis (see Fig. 1 A).

Bottom Line: Adherens junctions (AJs) often direct this polarity, but we previously found that Bazooka (Baz) acts upstream of AJs as epithelial polarity is first established in Drosophila.Surprisingly, we found that Baz localizes to an apical domain below its typical binding partners atypical protein kinase C (aPKC) and partitioning defective (PAR)-6 as the Drosophila epithelium first forms.These results reveal key steps in the assembly of the apical domain in Drosophila.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA. tonyh@email.unc.edu

ABSTRACT
Cell polarity is critical for epithelial structure and function. Adherens junctions (AJs) often direct this polarity, but we previously found that Bazooka (Baz) acts upstream of AJs as epithelial polarity is first established in Drosophila. This prompted us to ask how Baz is positioned and how downstream polarity is elaborated. Surprisingly, we found that Baz localizes to an apical domain below its typical binding partners atypical protein kinase C (aPKC) and partitioning defective (PAR)-6 as the Drosophila epithelium first forms. In fact, Baz positioning is independent of aPKC and PAR-6 relying instead on cytoskeletal cues, including an apical scaffold and dynein-mediated basal-to-apical transport. AJ assembly is closely coupled to Baz positioning, whereas aPKC and PAR-6 are positioned separately. This forms a stratified apical domain with Baz and AJs localizing basal to aPKC and PAR-6, and we identify specific mechanisms that keep these proteins apart. These results reveal key steps in the assembly of the apical domain in Drosophila.

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