Limits...
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.

Show MeSH

Related in: MedlinePlus

Baz acts upstream of aPKC as epithelial polarity is established. (A) WT cellularization. aPKC (red) apical. (B and C) bazm/z mutants. (B) Cellularization. aPKC (red) mislocalized basally. PAR-6 (green) cortical and cytoplasmic. (C) Gastrulation. aPKC (red) still basally mislocalized. PAR-6 (green) has some apical enrichment. (D–F) apkcm/z mutants, cellularization. (D) Cross section. Baz (red) and DE-Cad (green) are apical. (E) Surface view. Baz (red) and DE-Cad (green) colocalize in spot junctions, similar to WT (insets). (F) PAR-6 (green) is cytoplasmic. (G) apkcm/z mutant, stage 8 (late gastrulation). Surface view. Baz (red) and DE-Cad (green) colocalize in discontinuous cortical patches (WT junctions are continuous; insets). Bars, 5 μm.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2171335&req=5

fig2: Baz acts upstream of aPKC as epithelial polarity is established. (A) WT cellularization. aPKC (red) apical. (B and C) bazm/z mutants. (B) Cellularization. aPKC (red) mislocalized basally. PAR-6 (green) cortical and cytoplasmic. (C) Gastrulation. aPKC (red) still basally mislocalized. PAR-6 (green) has some apical enrichment. (D–F) apkcm/z mutants, cellularization. (D) Cross section. Baz (red) and DE-Cad (green) are apical. (E) Surface view. Baz (red) and DE-Cad (green) colocalize in spot junctions, similar to WT (insets). (F) PAR-6 (green) is cytoplasmic. (G) apkcm/z mutant, stage 8 (late gastrulation). Surface view. Baz (red) and DE-Cad (green) colocalize in discontinuous cortical patches (WT junctions are continuous; insets). Bars, 5 μm.

Mentions: Our previous work implicated Baz as a primary apical landmark during cellularization (Harris and Peifer, 2004). Considering both Baz and aPKC localize apically as polarity is established, we wondered whether one functions upstream to position the other. To address this, we first analyzed aPKC localization in cellularizing baz maternal/zygotic (m/z) mutants. In bazm/z mutants, aPKC is mislocalized along the full furrow length (Fig. 2 B, bracket), in contrast to its apical wild-type (WT) localization (Figs. 1 D and 2 A, arrow). Thus, Baz is required for aPKC positioning during cellularization. PAR-6 has a nonpolarized cytoplasmic and cortical distribution in bazm/z mutants (Fig. 2 B), as in WT (Fig. 1 E). As bazm/z mutants begin gastrulation, aPKC remains basally mislocalized (Fig. 2 C, bracket), but PAR-6 shows some apical enrichment (Fig. 2 C, arrows). Thus, although Baz is required for apical aPKC positioning, later PAR-6 positioning may be partially Baz independent.


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

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

Baz acts upstream of aPKC as epithelial polarity is established. (A) WT cellularization. aPKC (red) apical. (B and C) bazm/z mutants. (B) Cellularization. aPKC (red) mislocalized basally. PAR-6 (green) cortical and cytoplasmic. (C) Gastrulation. aPKC (red) still basally mislocalized. PAR-6 (green) has some apical enrichment. (D–F) apkcm/z mutants, cellularization. (D) Cross section. Baz (red) and DE-Cad (green) are apical. (E) Surface view. Baz (red) and DE-Cad (green) colocalize in spot junctions, similar to WT (insets). (F) PAR-6 (green) is cytoplasmic. (G) apkcm/z mutant, stage 8 (late gastrulation). Surface view. Baz (red) and DE-Cad (green) colocalize in discontinuous cortical patches (WT junctions are continuous; insets). Bars, 5 μm.
© Copyright Policy
Related In: Results  -  Collection

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

fig2: Baz acts upstream of aPKC as epithelial polarity is established. (A) WT cellularization. aPKC (red) apical. (B and C) bazm/z mutants. (B) Cellularization. aPKC (red) mislocalized basally. PAR-6 (green) cortical and cytoplasmic. (C) Gastrulation. aPKC (red) still basally mislocalized. PAR-6 (green) has some apical enrichment. (D–F) apkcm/z mutants, cellularization. (D) Cross section. Baz (red) and DE-Cad (green) are apical. (E) Surface view. Baz (red) and DE-Cad (green) colocalize in spot junctions, similar to WT (insets). (F) PAR-6 (green) is cytoplasmic. (G) apkcm/z mutant, stage 8 (late gastrulation). Surface view. Baz (red) and DE-Cad (green) colocalize in discontinuous cortical patches (WT junctions are continuous; insets). Bars, 5 μm.
Mentions: Our previous work implicated Baz as a primary apical landmark during cellularization (Harris and Peifer, 2004). Considering both Baz and aPKC localize apically as polarity is established, we wondered whether one functions upstream to position the other. To address this, we first analyzed aPKC localization in cellularizing baz maternal/zygotic (m/z) mutants. In bazm/z mutants, aPKC is mislocalized along the full furrow length (Fig. 2 B, bracket), in contrast to its apical wild-type (WT) localization (Figs. 1 D and 2 A, arrow). Thus, Baz is required for aPKC positioning during cellularization. PAR-6 has a nonpolarized cytoplasmic and cortical distribution in bazm/z mutants (Fig. 2 B), as in WT (Fig. 1 E). As bazm/z mutants begin gastrulation, aPKC remains basally mislocalized (Fig. 2 C, bracket), but PAR-6 shows some apical enrichment (Fig. 2 C, arrows). Thus, although Baz is required for apical aPKC positioning, later PAR-6 positioning may be partially Baz independent.

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
Related in: MedlinePlus