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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 is in proximity to the actin and MT cytoskeletons during WT cellularization. (A) Cross section. Baz (red) at the base of the apical actin meshwork (green; actin decorated with the actin binding domain of moesin fused to GFP). (B) Cross section. Apical Baz (red) next to longitudinal MTs (green). (C) Surface view. Apical Baz (red) has minimal overlap with MTs (green). (D) 10 μm deep cross section. Apical Baz (red) next to centrosomes (γ-tubulin, green). (E) Surface view. Apical Baz (red) next to centrosomes (γ-tubulin, green). (F) Schematic of apical Baz in proximity to cytoskeletal cues. Bars, 5 μm.
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fig3: Baz is in proximity to the actin and MT cytoskeletons during WT cellularization. (A) Cross section. Baz (red) at the base of the apical actin meshwork (green; actin decorated with the actin binding domain of moesin fused to GFP). (B) Cross section. Apical Baz (red) next to longitudinal MTs (green). (C) Surface view. Apical Baz (red) has minimal overlap with MTs (green). (D) 10 μm deep cross section. Apical Baz (red) next to centrosomes (γ-tubulin, green). (E) Surface view. Apical Baz (red) next to centrosomes (γ-tubulin, green). (F) Schematic of apical Baz in proximity to cytoskeletal cues. Bars, 5 μm.

Mentions: Baz is required for positioning AJs and aPKC as polarity is established during cellularization (Harris and Peifer, 2004; Fig. 2), but what upstream cues position Baz? Considering cellularization requires preexisting cytoskeletal polarity, we hypothesized that cytoskeletal cues might position apical Baz. To test this, we first examined Baz localization relative to actin and MTs during WT cellularization. Actin is enriched in furrow canals at the base of invaginating furrows (Fig. 3 A, yellow arrowhead), and in an apical meshwork (Fig. 3 A arrowhead; lower actin levels are along the full furrow length). Baz is not enriched at basal furrow canals, but does overlap with the apical actin meshwork, although only at its basal edge (Fig. 3 A, arrow).


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

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

Baz is in proximity to the actin and MT cytoskeletons during WT cellularization. (A) Cross section. Baz (red) at the base of the apical actin meshwork (green; actin decorated with the actin binding domain of moesin fused to GFP). (B) Cross section. Apical Baz (red) next to longitudinal MTs (green). (C) Surface view. Apical Baz (red) has minimal overlap with MTs (green). (D) 10 μm deep cross section. Apical Baz (red) next to centrosomes (γ-tubulin, green). (E) Surface view. Apical Baz (red) next to centrosomes (γ-tubulin, green). (F) Schematic of apical Baz in proximity to cytoskeletal cues. Bars, 5 μm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2171335&req=5

fig3: Baz is in proximity to the actin and MT cytoskeletons during WT cellularization. (A) Cross section. Baz (red) at the base of the apical actin meshwork (green; actin decorated with the actin binding domain of moesin fused to GFP). (B) Cross section. Apical Baz (red) next to longitudinal MTs (green). (C) Surface view. Apical Baz (red) has minimal overlap with MTs (green). (D) 10 μm deep cross section. Apical Baz (red) next to centrosomes (γ-tubulin, green). (E) Surface view. Apical Baz (red) next to centrosomes (γ-tubulin, green). (F) Schematic of apical Baz in proximity to cytoskeletal cues. Bars, 5 μm.
Mentions: Baz is required for positioning AJs and aPKC as polarity is established during cellularization (Harris and Peifer, 2004; Fig. 2), but what upstream cues position Baz? Considering cellularization requires preexisting cytoskeletal polarity, we hypothesized that cytoskeletal cues might position apical Baz. To test this, we first examined Baz localization relative to actin and MTs during WT cellularization. Actin is enriched in furrow canals at the base of invaginating furrows (Fig. 3 A, yellow arrowhead), and in an apical meshwork (Fig. 3 A arrowhead; lower actin levels are along the full furrow length). Baz is not enriched at basal furrow canals, but does overlap with the apical actin meshwork, although only at its basal edge (Fig. 3 A, arrow).

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.

Show MeSH