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Apical, lateral, and basal polarization cues contribute to the development of the follicular epithelium during Drosophila oogenesis.

Tanentzapf G, Smith C, McGlade J, Tepass U - J. Cell Biol. (2000)

Bottom Line: Loss of cadherin-based adherens junctions caused by armadillo (beta-catenin) mutations results in a disruption of the lateral spectrin and actin cytoskeleton.Also Crb and the apical spectrin cytoskeleton are lost from armadillo mutant follicle cells.Together with previous data showing that Crb is required for the formation of a zonula adherens, these findings indicate a mutual dependency of apical and lateral polarization mechanisms.

View Article: PubMed Central - PubMed

Affiliation: Department of Zoology, University of Toronto, Toronto, Ontario, Canada M5S 3G5.

ABSTRACT
Analysis of the mechanisms that control epithelial polarization has revealed that cues for polarization are mediated by transmembrane proteins that operate at the apical, lateral, or basal surface of epithelial cells. Whereas for any given epithelial cell type only one or two polarization systems have been identified to date, we report here that the follicular epithelium in Drosophila ovaries uses three different polarization mechanisms, each operating at one of the three main epithelial surface domains. The follicular epithelium arises through a mesenchymal-epithelial transition. Contact with the basement membrane provides an initial polarization cue that leads to the formation of a basal membrane domain. Moreover, we use mosaic analysis to show that Crumbs (Crb) is required for the formation and maintenance of the follicular epithelium. Crb localizes to the apical membrane of follicle cells that is in contact with germline cells. Contact to the germline is required for the accumulation of Crb in follicle cells. Discs Lost (Dlt), a cytoplasmic PDZ domain protein that was shown to interact with the cytoplasmic tail of Crb, overlaps precisely in its distribution with Crb, as shown by immunoelectron microscopy. Crb localization depends on Dlt, whereas Dlt uses Crb-dependent and -independent mechanisms for apical targeting. Finally, we show that the cadherin-catenin complex is not required for the formation of the follicular epithelium, but only for its maintenance. Loss of cadherin-based adherens junctions caused by armadillo (beta-catenin) mutations results in a disruption of the lateral spectrin and actin cytoskeleton. Also Crb and the apical spectrin cytoskeleton are lost from armadillo mutant follicle cells. Together with previous data showing that Crb is required for the formation of a zonula adherens, these findings indicate a mutual dependency of apical and lateral polarization mechanisms.

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Distribution of F-actin, α-Spectrin (α-Spec) and βHeavy-Spectrin (βH-Spec) in arm mutant follicle cells. (A–C) armXP33 mutant follicle cells (arrowheads point to clone boundary) show a strong reduction at the lateral membrane and an apical accumulation of F-actin (A) and α-Spectrin (B). Normal amounts of βHeavy-Spectrin are associated with the apical membrane in armXP33 mutant cells (C). (D and E) Follicle cells mutant for armXK22 (arrowheads) have a flat cell shape and show a reduction in the size of the lateral membrane domain as indicated by the α-Spectrin staining (arrows). Apical βHeavy-Spectrin is lost from armXK22 mutant follicle cells (E). (F) armYD35 mutant follicle cells (below arrowhead) show squamous cell morphology in this stage 10 follicle. Nuclei are stained blue in E and F.
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Figure 9: Distribution of F-actin, α-Spectrin (α-Spec) and βHeavy-Spectrin (βH-Spec) in arm mutant follicle cells. (A–C) armXP33 mutant follicle cells (arrowheads point to clone boundary) show a strong reduction at the lateral membrane and an apical accumulation of F-actin (A) and α-Spectrin (B). Normal amounts of βHeavy-Spectrin are associated with the apical membrane in armXP33 mutant cells (C). (D and E) Follicle cells mutant for armXK22 (arrowheads) have a flat cell shape and show a reduction in the size of the lateral membrane domain as indicated by the α-Spectrin staining (arrows). Apical βHeavy-Spectrin is lost from armXK22 mutant follicle cells (E). (F) armYD35 mutant follicle cells (below arrowhead) show squamous cell morphology in this stage 10 follicle. Nuclei are stained blue in E and F.

Mentions: We took advantage of the fact that arm mutant cells in the FE are maintained for several days and analyzed their molecular architecture. armXP33 mutant follicle cells (see also Müller 2000), which in most cases have a normal cuboidal to columnar shape, show a decrease of F-actin and α-spectrin at the lateral membrane, and an accumulation of these molecules at the apical cell pole (Fig. 9A and Fig. B). In contrast, the apical marker βHeavy-spectrin shows a normal distribution in armXP33 mutant cells (Fig. 9 C), suggesting that the apical spectrin cytoskeleton is intact. Follicle cells mutant for armXK22 or armYD35 often develop a squamous cell morphology (Fig. 9, D–F) or show a multilayered structure. α-Spectrin remains associated with the narrow lateral membranes in squamous arm mutant cells (Fig. 9 D). βHeavy-Spectrin, on the other hand, is lost from these follicle cells, suggesting that the apical spectrin cytoskeleton is disrupted (Fig. 9 E). To further examine the apical surface domain of arm mutant follicle cells, we studied the distribution of Crb and Dlt in these cells. armXP33 mutant follicle cells show typically a normal apical localization of Crb and Dlt (Fig. 10A and Fig. B). In contrast, Crb is lost from the apical membrane of follicle cells mutant for strong arm alleles, whereas apical Dlt is retained in these cells (Fig. 10, C–E). Similar to dltdre1 mutant cell clones, Dlt forms a cap in the center of the apical membrane of arm mutant follicle cells. These observations suggest that the disruption of adherens junctions leads to a breakdown of the lateral membrane domain, as expected, but also compromises the apical surface domain. The differential behavior of Crb and Dlt in strong arm mutant cell clones again emphasizes that Dlt can rely on a Crb-independent apical targeting mechanism, and shows that apical Dlt can be retained in the absence of an apical spectrin cytoskeleton.


Apical, lateral, and basal polarization cues contribute to the development of the follicular epithelium during Drosophila oogenesis.

Tanentzapf G, Smith C, McGlade J, Tepass U - J. Cell Biol. (2000)

Distribution of F-actin, α-Spectrin (α-Spec) and βHeavy-Spectrin (βH-Spec) in arm mutant follicle cells. (A–C) armXP33 mutant follicle cells (arrowheads point to clone boundary) show a strong reduction at the lateral membrane and an apical accumulation of F-actin (A) and α-Spectrin (B). Normal amounts of βHeavy-Spectrin are associated with the apical membrane in armXP33 mutant cells (C). (D and E) Follicle cells mutant for armXK22 (arrowheads) have a flat cell shape and show a reduction in the size of the lateral membrane domain as indicated by the α-Spectrin staining (arrows). Apical βHeavy-Spectrin is lost from armXK22 mutant follicle cells (E). (F) armYD35 mutant follicle cells (below arrowhead) show squamous cell morphology in this stage 10 follicle. Nuclei are stained blue in E and F.
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Related In: Results  -  Collection

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Figure 9: Distribution of F-actin, α-Spectrin (α-Spec) and βHeavy-Spectrin (βH-Spec) in arm mutant follicle cells. (A–C) armXP33 mutant follicle cells (arrowheads point to clone boundary) show a strong reduction at the lateral membrane and an apical accumulation of F-actin (A) and α-Spectrin (B). Normal amounts of βHeavy-Spectrin are associated with the apical membrane in armXP33 mutant cells (C). (D and E) Follicle cells mutant for armXK22 (arrowheads) have a flat cell shape and show a reduction in the size of the lateral membrane domain as indicated by the α-Spectrin staining (arrows). Apical βHeavy-Spectrin is lost from armXK22 mutant follicle cells (E). (F) armYD35 mutant follicle cells (below arrowhead) show squamous cell morphology in this stage 10 follicle. Nuclei are stained blue in E and F.
Mentions: We took advantage of the fact that arm mutant cells in the FE are maintained for several days and analyzed their molecular architecture. armXP33 mutant follicle cells (see also Müller 2000), which in most cases have a normal cuboidal to columnar shape, show a decrease of F-actin and α-spectrin at the lateral membrane, and an accumulation of these molecules at the apical cell pole (Fig. 9A and Fig. B). In contrast, the apical marker βHeavy-spectrin shows a normal distribution in armXP33 mutant cells (Fig. 9 C), suggesting that the apical spectrin cytoskeleton is intact. Follicle cells mutant for armXK22 or armYD35 often develop a squamous cell morphology (Fig. 9, D–F) or show a multilayered structure. α-Spectrin remains associated with the narrow lateral membranes in squamous arm mutant cells (Fig. 9 D). βHeavy-Spectrin, on the other hand, is lost from these follicle cells, suggesting that the apical spectrin cytoskeleton is disrupted (Fig. 9 E). To further examine the apical surface domain of arm mutant follicle cells, we studied the distribution of Crb and Dlt in these cells. armXP33 mutant follicle cells show typically a normal apical localization of Crb and Dlt (Fig. 10A and Fig. B). In contrast, Crb is lost from the apical membrane of follicle cells mutant for strong arm alleles, whereas apical Dlt is retained in these cells (Fig. 10, C–E). Similar to dltdre1 mutant cell clones, Dlt forms a cap in the center of the apical membrane of arm mutant follicle cells. These observations suggest that the disruption of adherens junctions leads to a breakdown of the lateral membrane domain, as expected, but also compromises the apical surface domain. The differential behavior of Crb and Dlt in strong arm mutant cell clones again emphasizes that Dlt can rely on a Crb-independent apical targeting mechanism, and shows that apical Dlt can be retained in the absence of an apical spectrin cytoskeleton.

Bottom Line: Loss of cadherin-based adherens junctions caused by armadillo (beta-catenin) mutations results in a disruption of the lateral spectrin and actin cytoskeleton.Also Crb and the apical spectrin cytoskeleton are lost from armadillo mutant follicle cells.Together with previous data showing that Crb is required for the formation of a zonula adherens, these findings indicate a mutual dependency of apical and lateral polarization mechanisms.

View Article: PubMed Central - PubMed

Affiliation: Department of Zoology, University of Toronto, Toronto, Ontario, Canada M5S 3G5.

ABSTRACT
Analysis of the mechanisms that control epithelial polarization has revealed that cues for polarization are mediated by transmembrane proteins that operate at the apical, lateral, or basal surface of epithelial cells. Whereas for any given epithelial cell type only one or two polarization systems have been identified to date, we report here that the follicular epithelium in Drosophila ovaries uses three different polarization mechanisms, each operating at one of the three main epithelial surface domains. The follicular epithelium arises through a mesenchymal-epithelial transition. Contact with the basement membrane provides an initial polarization cue that leads to the formation of a basal membrane domain. Moreover, we use mosaic analysis to show that Crumbs (Crb) is required for the formation and maintenance of the follicular epithelium. Crb localizes to the apical membrane of follicle cells that is in contact with germline cells. Contact to the germline is required for the accumulation of Crb in follicle cells. Discs Lost (Dlt), a cytoplasmic PDZ domain protein that was shown to interact with the cytoplasmic tail of Crb, overlaps precisely in its distribution with Crb, as shown by immunoelectron microscopy. Crb localization depends on Dlt, whereas Dlt uses Crb-dependent and -independent mechanisms for apical targeting. Finally, we show that the cadherin-catenin complex is not required for the formation of the follicular epithelium, but only for its maintenance. Loss of cadherin-based adherens junctions caused by armadillo (beta-catenin) mutations results in a disruption of the lateral spectrin and actin cytoskeleton. Also Crb and the apical spectrin cytoskeleton are lost from armadillo mutant follicle cells. Together with previous data showing that Crb is required for the formation of a zonula adherens, these findings indicate a mutual dependency of apical and lateral polarization mechanisms.

Show MeSH