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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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Embryos expressing Cdc42-DN lose apical and AJ markers from the ventral neuroectoderm. (A and B) Wild-type embryo (A) and Cdc42-DN embryo (B) labeled for the AJ marker Arm. (C and D) Wild-type embryo (C) and Cdc42-DN embryo (D) labeled for the AJ marker Ed. (E–H) Wild-type embryo (E), Cdc42-DN embryos (F and G), and Cdc42-DN Nintra embryo (H) labeled for the apical marker Crb. Arrows indicate cytoplasmic accumulations of Crb. (I and J) Wild-type embryo (I) and Cdc42-DN embryo (J) labeled for the apical marker Notch (N). Arrows indicate cytoplasmic accumulations of Notch. (K and L) Wild-type embryo (K) and Cdc42-DN embryo (L) labeled for the apical marker Cad87A. Arrows indicate cytoplasmic accumulations of Cad87A. (M and N) Wild-type embryo (M) and Cdc42-DN embryo (N) labeled for the basolateral marker Nrt. (O and P) Wild-type embryo (O) and Cdc42-DN embryo (P) labeled for the basolateral marker Scrib. M, ventral midline; VNE, ventral neuroectoderm; DE, dorsal ectoderm. Bars: (A–F and H–P) 20 μm; (G) 10 μm.
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fig2: Embryos expressing Cdc42-DN lose apical and AJ markers from the ventral neuroectoderm. (A and B) Wild-type embryo (A) and Cdc42-DN embryo (B) labeled for the AJ marker Arm. (C and D) Wild-type embryo (C) and Cdc42-DN embryo (D) labeled for the AJ marker Ed. (E–H) Wild-type embryo (E), Cdc42-DN embryos (F and G), and Cdc42-DN Nintra embryo (H) labeled for the apical marker Crb. Arrows indicate cytoplasmic accumulations of Crb. (I and J) Wild-type embryo (I) and Cdc42-DN embryo (J) labeled for the apical marker Notch (N). Arrows indicate cytoplasmic accumulations of Notch. (K and L) Wild-type embryo (K) and Cdc42-DN embryo (L) labeled for the apical marker Cad87A. Arrows indicate cytoplasmic accumulations of Cad87A. (M and N) Wild-type embryo (M) and Cdc42-DN embryo (N) labeled for the basolateral marker Nrt. (O and P) Wild-type embryo (O) and Cdc42-DN embryo (P) labeled for the basolateral marker Scrib. M, ventral midline; VNE, ventral neuroectoderm; DE, dorsal ectoderm. Bars: (A–F and H–P) 20 μm; (G) 10 μm.

Mentions: To further characterize the neuroectodermal defects in da>Cdc42-DN embryos, we examined additional molecular makers that highlight AJs and the apical and basolateral membrane of neuroectodermal cells. In addition to DEcad (Fig. 1), we found that the AJ markers Armadillo (Arm; Drosophila β-catenin), Echinoid (Ed), and α-catenin were also lost from the apicolateral membrane, confirming the loss of AJs (Fig. 2, A–D; and not depicted). The apical determinant and transmembrane protein Crb and its binding partner Patj, which are enriched in the marginal zone immediately apical to the AJs, were also depleted from the apical membrane of neuroectodermal cells (Fig. 2, E–G; and not depicted). As with AJ markers, we found that the apical localization of Crb was restored in da>Cdc42-DN embryos that express Nintra (Fig. 2 H).


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)

Embryos expressing Cdc42-DN lose apical and AJ markers from the ventral neuroectoderm. (A and B) Wild-type embryo (A) and Cdc42-DN embryo (B) labeled for the AJ marker Arm. (C and D) Wild-type embryo (C) and Cdc42-DN embryo (D) labeled for the AJ marker Ed. (E–H) Wild-type embryo (E), Cdc42-DN embryos (F and G), and Cdc42-DN Nintra embryo (H) labeled for the apical marker Crb. Arrows indicate cytoplasmic accumulations of Crb. (I and J) Wild-type embryo (I) and Cdc42-DN embryo (J) labeled for the apical marker Notch (N). Arrows indicate cytoplasmic accumulations of Notch. (K and L) Wild-type embryo (K) and Cdc42-DN embryo (L) labeled for the apical marker Cad87A. Arrows indicate cytoplasmic accumulations of Cad87A. (M and N) Wild-type embryo (M) and Cdc42-DN embryo (N) labeled for the basolateral marker Nrt. (O and P) Wild-type embryo (O) and Cdc42-DN embryo (P) labeled for the basolateral marker Scrib. M, ventral midline; VNE, ventral neuroectoderm; DE, dorsal ectoderm. Bars: (A–F and H–P) 20 μm; (G) 10 μm.
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fig2: Embryos expressing Cdc42-DN lose apical and AJ markers from the ventral neuroectoderm. (A and B) Wild-type embryo (A) and Cdc42-DN embryo (B) labeled for the AJ marker Arm. (C and D) Wild-type embryo (C) and Cdc42-DN embryo (D) labeled for the AJ marker Ed. (E–H) Wild-type embryo (E), Cdc42-DN embryos (F and G), and Cdc42-DN Nintra embryo (H) labeled for the apical marker Crb. Arrows indicate cytoplasmic accumulations of Crb. (I and J) Wild-type embryo (I) and Cdc42-DN embryo (J) labeled for the apical marker Notch (N). Arrows indicate cytoplasmic accumulations of Notch. (K and L) Wild-type embryo (K) and Cdc42-DN embryo (L) labeled for the apical marker Cad87A. Arrows indicate cytoplasmic accumulations of Cad87A. (M and N) Wild-type embryo (M) and Cdc42-DN embryo (N) labeled for the basolateral marker Nrt. (O and P) Wild-type embryo (O) and Cdc42-DN embryo (P) labeled for the basolateral marker Scrib. M, ventral midline; VNE, ventral neuroectoderm; DE, dorsal ectoderm. Bars: (A–F and H–P) 20 μm; (G) 10 μm.
Mentions: To further characterize the neuroectodermal defects in da>Cdc42-DN embryos, we examined additional molecular makers that highlight AJs and the apical and basolateral membrane of neuroectodermal cells. In addition to DEcad (Fig. 1), we found that the AJ markers Armadillo (Arm; Drosophila β-catenin), Echinoid (Ed), and α-catenin were also lost from the apicolateral membrane, confirming the loss of AJs (Fig. 2, A–D; and not depicted). The apical determinant and transmembrane protein Crb and its binding partner Patj, which are enriched in the marginal zone immediately apical to the AJs, were also depleted from the apical membrane of neuroectodermal cells (Fig. 2, E–G; and not depicted). As with AJ markers, we found that the apical localization of Crb was restored in da>Cdc42-DN embryos that express Nintra (Fig. 2 H).

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