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Cdc42 and Par proteins stabilize dynamic adherens junctions in the Drosophila neuroectoderm through regulation of apical endocytosis.

Harris KP, Tepass U - J. Cell Biol. (2008)

Bottom Line: Loss of Cdc42 function caused an increase in the endocytotic uptake of apical proteins, including apical polarity factors such as Crumbs, which are required for AJ stability.The Par complex acts as an effector for Cdc42 in controlling the endocytosis of apical proteins.This study reveals functional interactions between apical polarity proteins and endocytosis that are critical for stabilizing dynamic basolateral AJs.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell and Systems Biology, University of Toronto, Toronto, Ontario M5S 3G5, Canada.

ABSTRACT
Cell rearrangements require dynamic changes in cell-cell contacts to maintain tissue integrity. We investigated the function of Cdc42 in maintaining adherens junctions (AJs) and apical polarity in the Drosophila melanogaster neuroectodermal epithelium. About one third of cells exit the epithelium through ingression and become neuroblasts. Cdc42-compromised embryos lost AJs in the neuroectoderm during neuroblast ingression. In contrast, when neuroblast formation was suppressed, AJs were maintained despite the loss of Cdc42 function. Loss of Cdc42 function caused an increase in the endocytotic uptake of apical proteins, including apical polarity factors such as Crumbs, which are required for AJ stability. In addition, Cdc42 has a second function in regulating endocytotic trafficking, as it is required for the progression of apical cargo from the early to the late endosome. The Par complex acts as an effector for Cdc42 in controlling the endocytosis of apical proteins. This study reveals functional interactions between apical polarity proteins and endocytosis that are critical for stabilizing dynamic basolateral AJs.

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Activated aPKC rescues defects in Cdc42-DN embryos. (A–C) Wild-type embryo (A), Cdc42-DN embryo (B), and embryo expressing both Cdc42-DN and aPKCCAAXWT under the control of da-Gal4 (C) labeled with DEcad. (D–F) Wild-type (D), Cdc42-DN (E), and Cdc42-DN, aPKCCAAXWT (F) embryos labeled for Crb. (G) The extent of ventral cuticle defects was quantified by counting the number of intact abdominal denticle belts (mean ± SEM [error bars]). For Cdc42-DN, aPKCCAAXWT embryos, the difference in the mean number of intact belts relative to Cdc42-DN embryos is statistically significant (P < 0.001). (H) Ventral cuticle of da-Gal4, Cdc42-DN, aPKCCAAXWT embryo. M, ventral midline; VNE, ventral neuroectoderm; DE, dorsal ectoderm. Bars: (A–G) 20 μm; (H) 100 μm.
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fig9: Activated aPKC rescues defects in Cdc42-DN embryos. (A–C) Wild-type embryo (A), Cdc42-DN embryo (B), and embryo expressing both Cdc42-DN and aPKCCAAXWT under the control of da-Gal4 (C) labeled with DEcad. (D–F) Wild-type (D), Cdc42-DN (E), and Cdc42-DN, aPKCCAAXWT (F) embryos labeled for Crb. (G) The extent of ventral cuticle defects was quantified by counting the number of intact abdominal denticle belts (mean ± SEM [error bars]). For Cdc42-DN, aPKCCAAXWT embryos, the difference in the mean number of intact belts relative to Cdc42-DN embryos is statistically significant (P < 0.001). (H) Ventral cuticle of da-Gal4, Cdc42-DN, aPKCCAAXWT embryo. M, ventral midline; VNE, ventral neuroectoderm; DE, dorsal ectoderm. Bars: (A–G) 20 μm; (H) 100 μm.

Mentions: To test whether the Par complex acts downstream and, thus, most likely as an effector complex of Cdc42 in the regulation of endocytosis, we coexpressed a CA form of aPKC (aPKCCAAXWT; Sotillos et al., 2004) and Cdc42-DN. Expression of aPKCCAAXWT strongly suppresses the phenotype of da>Cdc42-DN embryos; localization of apical proteins, including Crb and DEcad (Fig. 9, A–F), is partially restored, and ventral cuticle defects are ameliorated (Fig. 9, G and H). Moreover, the formation of enlarged endosomes containing an abnormal accumulation of apical cargo is completely abolished (Fig. 9 F and not depicted). We conclude that aPKC acts downstream of Cdc42 in the regulation of apical endocytosis.


Cdc42 and Par proteins stabilize dynamic adherens junctions in the Drosophila neuroectoderm through regulation of apical endocytosis.

Harris KP, Tepass U - J. Cell Biol. (2008)

Activated aPKC rescues defects in Cdc42-DN embryos. (A–C) Wild-type embryo (A), Cdc42-DN embryo (B), and embryo expressing both Cdc42-DN and aPKCCAAXWT under the control of da-Gal4 (C) labeled with DEcad. (D–F) Wild-type (D), Cdc42-DN (E), and Cdc42-DN, aPKCCAAXWT (F) embryos labeled for Crb. (G) The extent of ventral cuticle defects was quantified by counting the number of intact abdominal denticle belts (mean ± SEM [error bars]). For Cdc42-DN, aPKCCAAXWT embryos, the difference in the mean number of intact belts relative to Cdc42-DN embryos is statistically significant (P < 0.001). (H) Ventral cuticle of da-Gal4, Cdc42-DN, aPKCCAAXWT embryo. M, ventral midline; VNE, ventral neuroectoderm; DE, dorsal ectoderm. Bars: (A–G) 20 μm; (H) 100 μm.
© Copyright Policy
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2600741&req=5

fig9: Activated aPKC rescues defects in Cdc42-DN embryos. (A–C) Wild-type embryo (A), Cdc42-DN embryo (B), and embryo expressing both Cdc42-DN and aPKCCAAXWT under the control of da-Gal4 (C) labeled with DEcad. (D–F) Wild-type (D), Cdc42-DN (E), and Cdc42-DN, aPKCCAAXWT (F) embryos labeled for Crb. (G) The extent of ventral cuticle defects was quantified by counting the number of intact abdominal denticle belts (mean ± SEM [error bars]). For Cdc42-DN, aPKCCAAXWT embryos, the difference in the mean number of intact belts relative to Cdc42-DN embryos is statistically significant (P < 0.001). (H) Ventral cuticle of da-Gal4, Cdc42-DN, aPKCCAAXWT embryo. M, ventral midline; VNE, ventral neuroectoderm; DE, dorsal ectoderm. Bars: (A–G) 20 μm; (H) 100 μm.
Mentions: To test whether the Par complex acts downstream and, thus, most likely as an effector complex of Cdc42 in the regulation of endocytosis, we coexpressed a CA form of aPKC (aPKCCAAXWT; Sotillos et al., 2004) and Cdc42-DN. Expression of aPKCCAAXWT strongly suppresses the phenotype of da>Cdc42-DN embryos; localization of apical proteins, including Crb and DEcad (Fig. 9, A–F), is partially restored, and ventral cuticle defects are ameliorated (Fig. 9, G and H). Moreover, the formation of enlarged endosomes containing an abnormal accumulation of apical cargo is completely abolished (Fig. 9 F and not depicted). We conclude that aPKC acts downstream of Cdc42 in the regulation of apical endocytosis.

Bottom Line: Loss of Cdc42 function caused an increase in the endocytotic uptake of apical proteins, including apical polarity factors such as Crumbs, which are required for AJ stability.The Par complex acts as an effector for Cdc42 in controlling the endocytosis of apical proteins.This study reveals functional interactions between apical polarity proteins and endocytosis that are critical for stabilizing dynamic basolateral AJs.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell and Systems Biology, University of Toronto, Toronto, Ontario M5S 3G5, Canada.

ABSTRACT
Cell rearrangements require dynamic changes in cell-cell contacts to maintain tissue integrity. We investigated the function of Cdc42 in maintaining adherens junctions (AJs) and apical polarity in the Drosophila melanogaster neuroectodermal epithelium. About one third of cells exit the epithelium through ingression and become neuroblasts. Cdc42-compromised embryos lost AJs in the neuroectoderm during neuroblast ingression. In contrast, when neuroblast formation was suppressed, AJs were maintained despite the loss of Cdc42 function. Loss of Cdc42 function caused an increase in the endocytotic uptake of apical proteins, including apical polarity factors such as Crumbs, which are required for AJ stability. In addition, Cdc42 has a second function in regulating endocytotic trafficking, as it is required for the progression of apical cargo from the early to the late endosome. The Par complex acts as an effector for Cdc42 in controlling the endocytosis of apical proteins. This study reveals functional interactions between apical polarity proteins and endocytosis that are critical for stabilizing dynamic basolateral AJs.

Show MeSH
Related in: MedlinePlus