Limits...
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.

Show MeSH

Related in: MedlinePlus

Internalization of FM4-64 in wild-type embryos and embryos expressing Cdc42-DN. (A and B) Neuroectoderm of wild-type (A and A′) and Cdc42-DN (B and B′) embryos labeled for Crb and the vital dye FM4-64. (C) FM4-64 labeling intensity was measured for individual confocal z stacks comprising ∼16 neuroectodermal cells (mean ± SEM [error bars]). Cdc42-DN embryos showed a substantial increase in FM4-64 uptake, as the observed difference in mean pixel intensity relative to the wild-type control is highly significant (P < 0.001). The differences between Cdc42-DN and wild-type embryos are the result of different particle sizes (P < 0.001; C′), whereas the particle number labeled by FM4-64 remained the same (C′′). Bars: (A and B) 10 μm; (A′ and B′) 5 μm.
© Copyright Policy
Related In: Results  -  Collection

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

fig4: Internalization of FM4-64 in wild-type embryos and embryos expressing Cdc42-DN. (A and B) Neuroectoderm of wild-type (A and A′) and Cdc42-DN (B and B′) embryos labeled for Crb and the vital dye FM4-64. (C) FM4-64 labeling intensity was measured for individual confocal z stacks comprising ∼16 neuroectodermal cells (mean ± SEM [error bars]). Cdc42-DN embryos showed a substantial increase in FM4-64 uptake, as the observed difference in mean pixel intensity relative to the wild-type control is highly significant (P < 0.001). The differences between Cdc42-DN and wild-type embryos are the result of different particle sizes (P < 0.001; C′), whereas the particle number labeled by FM4-64 remained the same (C′′). Bars: (A and B) 10 μm; (A′ and B′) 5 μm.

Mentions: Colocalization experiments revealed that the large Cdc42-positive puncta are the same puncta that accumulate apical membrane proteins in da>Cdc42-DN embryos (Fig. 3, J and K) and are therefore likely vesicular compartments in the biosynthetic or endosomal pathways. To determine whether these vesicles are biosynthetic or endosomal, we exposed live da>Cdc42-DN embryos to FM4-64, a dye that is taken up into cells through endocytosis and labels all endocytotic compartments. FM4-64 colocalized with Crb (Fig. 4, A and B) and other apical proteins to the large cytoplasmic vesicles in da>Cdc42-DN embryos, indicating that these are endocytotic compartments. Quantification of FM4-64 labeling intensity in the neuroectoderm of da>Cdc42-DN embryos compared with wild type indicated that endocytotic uptake of FM4-64 in da>Cdc42-DN embryos is significantly increased (Fig. 4 C). Moreover, although the number of FM4-64–labeled vesicles remained the same in mutant versus wild-type embryos, vesicles in da>Cdc42-DN embryos appeared significantly larger, accounting for the overall increase in labeling intensity. These findings suggest that loss of Cdc42 activity increases endocytosis in neuroectodermal cells.


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)

Internalization of FM4-64 in wild-type embryos and embryos expressing Cdc42-DN. (A and B) Neuroectoderm of wild-type (A and A′) and Cdc42-DN (B and B′) embryos labeled for Crb and the vital dye FM4-64. (C) FM4-64 labeling intensity was measured for individual confocal z stacks comprising ∼16 neuroectodermal cells (mean ± SEM [error bars]). Cdc42-DN embryos showed a substantial increase in FM4-64 uptake, as the observed difference in mean pixel intensity relative to the wild-type control is highly significant (P < 0.001). The differences between Cdc42-DN and wild-type embryos are the result of different particle sizes (P < 0.001; C′), whereas the particle number labeled by FM4-64 remained the same (C′′). Bars: (A and B) 10 μm; (A′ and B′) 5 μm.
© Copyright Policy
Related In: Results  -  Collection

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

fig4: Internalization of FM4-64 in wild-type embryos and embryos expressing Cdc42-DN. (A and B) Neuroectoderm of wild-type (A and A′) and Cdc42-DN (B and B′) embryos labeled for Crb and the vital dye FM4-64. (C) FM4-64 labeling intensity was measured for individual confocal z stacks comprising ∼16 neuroectodermal cells (mean ± SEM [error bars]). Cdc42-DN embryos showed a substantial increase in FM4-64 uptake, as the observed difference in mean pixel intensity relative to the wild-type control is highly significant (P < 0.001). The differences between Cdc42-DN and wild-type embryos are the result of different particle sizes (P < 0.001; C′), whereas the particle number labeled by FM4-64 remained the same (C′′). Bars: (A and B) 10 μm; (A′ and B′) 5 μm.
Mentions: Colocalization experiments revealed that the large Cdc42-positive puncta are the same puncta that accumulate apical membrane proteins in da>Cdc42-DN embryos (Fig. 3, J and K) and are therefore likely vesicular compartments in the biosynthetic or endosomal pathways. To determine whether these vesicles are biosynthetic or endosomal, we exposed live da>Cdc42-DN embryos to FM4-64, a dye that is taken up into cells through endocytosis and labels all endocytotic compartments. FM4-64 colocalized with Crb (Fig. 4, A and B) and other apical proteins to the large cytoplasmic vesicles in da>Cdc42-DN embryos, indicating that these are endocytotic compartments. Quantification of FM4-64 labeling intensity in the neuroectoderm of da>Cdc42-DN embryos compared with wild type indicated that endocytotic uptake of FM4-64 in da>Cdc42-DN embryos is significantly increased (Fig. 4 C). Moreover, although the number of FM4-64–labeled vesicles remained the same in mutant versus wild-type embryos, vesicles in da>Cdc42-DN embryos appeared significantly larger, accounting for the overall increase in labeling intensity. These findings suggest that loss of Cdc42 activity increases endocytosis in neuroectodermal cells.

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