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Apical spectrin is essential for epithelial morphogenesis but not apicobasal polarity in Drosophila.

Zarnescu DC, Thomas GH - J. Cell Biol. (1999)

Bottom Line: We report that apical beta(Heavy)-spectrin (beta(H)), a terminal web protein that is also associated with the zonula adherens, is essential for normal epithelial morphogenesis of the Drosophila follicle cell epithelium during oogenesis.Elimination of beta(H) prevents the stable recruitment of alpha-spectrin to the apical domain, but does not result in a loss of apicobasal polarity, as would be predicted from current models describing the role of spectrin in the establishment of cell polarity.These results demonstrate a direct role for apical (alphabeta(H))(2)-spectrin in epithelial morphogenesis driven by apical contraction, and suggest that apical and basolateral spectrin do not play identical roles in the generation of apicobasal polarity.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.

ABSTRACT
Changes in cell shape and position drive morphogenesis in epithelia and depend on the polarized nature of its constituent cells. The spectrin-based membrane skeleton is thought to be a key player in the establishment and/or maintenance of cell shape and polarity. We report that apical beta(Heavy)-spectrin (beta(H)), a terminal web protein that is also associated with the zonula adherens, is essential for normal epithelial morphogenesis of the Drosophila follicle cell epithelium during oogenesis. Elimination of beta(H) by the karst mutation prevents apical constriction of the follicle cells during mid-oogenesis, and is accompanied by a gross breakup of the zonula adherens. We also report that the integrity of the migratory border cell cluster, a group of anterior follicle cells that delaminates from the follicle epithelium, is disrupted. Elimination of beta(H) prevents the stable recruitment of alpha-spectrin to the apical domain, but does not result in a loss of apicobasal polarity, as would be predicted from current models describing the role of spectrin in the establishment of cell polarity. These results demonstrate a direct role for apical (alphabeta(H))(2)-spectrin in epithelial morphogenesis driven by apical contraction, and suggest that apical and basolateral spectrin do not play identical roles in the generation of apicobasal polarity.

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Border cell clusters are disrupted in karst mutant egg chambers. (A and B) Sagittal confocal sections of stage 10A and B mutant egg chambers stained for α-spectrin. Cells separated from the main border cell cluster (arrowheads) migrate either separately (A, arrow) or in a trail (B, arrow). All cells migrating between nurse cell membranes in karst mutant egg chambers express slbo. (C) β-Galactosidase activity staining marks the border cell cluster (black arrowhead) in slbo1/+ marked wild-type ovaries. (D–F) All cells migrating between the nurse cells in slbo1/+; kst ovaries, including the main border cell cluster (black arrowhead) and the separated cells (white arrows), express slbo. White asterisks indicate cells slightly off the focal plane that are shown again in focus in the corresponding marked insets. Insets marked with black asterisks show staining cells completely out of the main focal plane. All chambers are at stage 9 or 10A. β-Galactosidase activity staining was performed simultaneously with DAPI nuclear staining to ensure that all cells penetrating the nurse cell cluster were identified (data not shown). Scale bar represents 50 μm in A and B, 10 μm in D–F.
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Figure 6: Border cell clusters are disrupted in karst mutant egg chambers. (A and B) Sagittal confocal sections of stage 10A and B mutant egg chambers stained for α-spectrin. Cells separated from the main border cell cluster (arrowheads) migrate either separately (A, arrow) or in a trail (B, arrow). All cells migrating between nurse cell membranes in karst mutant egg chambers express slbo. (C) β-Galactosidase activity staining marks the border cell cluster (black arrowhead) in slbo1/+ marked wild-type ovaries. (D–F) All cells migrating between the nurse cells in slbo1/+; kst ovaries, including the main border cell cluster (black arrowhead) and the separated cells (white arrows), express slbo. White asterisks indicate cells slightly off the focal plane that are shown again in focus in the corresponding marked insets. Insets marked with black asterisks show staining cells completely out of the main focal plane. All chambers are at stage 9 or 10A. β-Galactosidase activity staining was performed simultaneously with DAPI nuclear staining to ensure that all cells penetrating the nurse cell cluster were identified (data not shown). Scale bar represents 50 μm in A and B, 10 μm in D–F.

Mentions: The border cell cluster delaminates from the follicle cell epithelium and migrates between the nurse cells to the anterior of the oocyte during stage 9. In ∼10% of karst mutant egg chambers, we observe migratory cells that are well separated from, or trail behind, the main border cell cluster (Fig. 6). The trailing cells upregulate α-spectrin (Fig. 6A and Fig. B) and DE-cadherin (data not shown) in a manner that resembles wild-type clusters, suggesting that they are true border cells. To confirm that these cells have a border cell fate, we looked for the expression of the border cell marker slow border cells (slbo) by introducing the enhancer trapped LacZ gene associated with the slbo1 P-element allele (Montell et al. 1992) into the karst mutant background and staining for β-galactosidase activity. All of the migratory cells in slbo1/+; kst egg chambers express β-galactosidase, although the intensity of staining exhibited by the separated cells is often lower than the main border cell cluster (Fig. 6, D–F). None of the trailing cells express Fasciclin III, indicating that they do not contain polar cells (data not shown; Patel et al. 1987), and thus do not represent second, independently organized, migratory clusters. Furthermore, the total number of β-galactosidase–positive cells ranges from 7 to 11, very close to the normal range in border cell number in wild-type chambers (6–10; Spradling 1993). Together, these data suggest that all of the migratory cells are bona fide border cells and that the normal number of border cells is specified in karst mutants, but that the cluster is unable to remain together as a unit.


Apical spectrin is essential for epithelial morphogenesis but not apicobasal polarity in Drosophila.

Zarnescu DC, Thomas GH - J. Cell Biol. (1999)

Border cell clusters are disrupted in karst mutant egg chambers. (A and B) Sagittal confocal sections of stage 10A and B mutant egg chambers stained for α-spectrin. Cells separated from the main border cell cluster (arrowheads) migrate either separately (A, arrow) or in a trail (B, arrow). All cells migrating between nurse cell membranes in karst mutant egg chambers express slbo. (C) β-Galactosidase activity staining marks the border cell cluster (black arrowhead) in slbo1/+ marked wild-type ovaries. (D–F) All cells migrating between the nurse cells in slbo1/+; kst ovaries, including the main border cell cluster (black arrowhead) and the separated cells (white arrows), express slbo. White asterisks indicate cells slightly off the focal plane that are shown again in focus in the corresponding marked insets. Insets marked with black asterisks show staining cells completely out of the main focal plane. All chambers are at stage 9 or 10A. β-Galactosidase activity staining was performed simultaneously with DAPI nuclear staining to ensure that all cells penetrating the nurse cell cluster were identified (data not shown). Scale bar represents 50 μm in A and B, 10 μm in D–F.
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Figure 6: Border cell clusters are disrupted in karst mutant egg chambers. (A and B) Sagittal confocal sections of stage 10A and B mutant egg chambers stained for α-spectrin. Cells separated from the main border cell cluster (arrowheads) migrate either separately (A, arrow) or in a trail (B, arrow). All cells migrating between nurse cell membranes in karst mutant egg chambers express slbo. (C) β-Galactosidase activity staining marks the border cell cluster (black arrowhead) in slbo1/+ marked wild-type ovaries. (D–F) All cells migrating between the nurse cells in slbo1/+; kst ovaries, including the main border cell cluster (black arrowhead) and the separated cells (white arrows), express slbo. White asterisks indicate cells slightly off the focal plane that are shown again in focus in the corresponding marked insets. Insets marked with black asterisks show staining cells completely out of the main focal plane. All chambers are at stage 9 or 10A. β-Galactosidase activity staining was performed simultaneously with DAPI nuclear staining to ensure that all cells penetrating the nurse cell cluster were identified (data not shown). Scale bar represents 50 μm in A and B, 10 μm in D–F.
Mentions: The border cell cluster delaminates from the follicle cell epithelium and migrates between the nurse cells to the anterior of the oocyte during stage 9. In ∼10% of karst mutant egg chambers, we observe migratory cells that are well separated from, or trail behind, the main border cell cluster (Fig. 6). The trailing cells upregulate α-spectrin (Fig. 6A and Fig. B) and DE-cadherin (data not shown) in a manner that resembles wild-type clusters, suggesting that they are true border cells. To confirm that these cells have a border cell fate, we looked for the expression of the border cell marker slow border cells (slbo) by introducing the enhancer trapped LacZ gene associated with the slbo1 P-element allele (Montell et al. 1992) into the karst mutant background and staining for β-galactosidase activity. All of the migratory cells in slbo1/+; kst egg chambers express β-galactosidase, although the intensity of staining exhibited by the separated cells is often lower than the main border cell cluster (Fig. 6, D–F). None of the trailing cells express Fasciclin III, indicating that they do not contain polar cells (data not shown; Patel et al. 1987), and thus do not represent second, independently organized, migratory clusters. Furthermore, the total number of β-galactosidase–positive cells ranges from 7 to 11, very close to the normal range in border cell number in wild-type chambers (6–10; Spradling 1993). Together, these data suggest that all of the migratory cells are bona fide border cells and that the normal number of border cells is specified in karst mutants, but that the cluster is unable to remain together as a unit.

Bottom Line: We report that apical beta(Heavy)-spectrin (beta(H)), a terminal web protein that is also associated with the zonula adherens, is essential for normal epithelial morphogenesis of the Drosophila follicle cell epithelium during oogenesis.Elimination of beta(H) prevents the stable recruitment of alpha-spectrin to the apical domain, but does not result in a loss of apicobasal polarity, as would be predicted from current models describing the role of spectrin in the establishment of cell polarity.These results demonstrate a direct role for apical (alphabeta(H))(2)-spectrin in epithelial morphogenesis driven by apical contraction, and suggest that apical and basolateral spectrin do not play identical roles in the generation of apicobasal polarity.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.

ABSTRACT
Changes in cell shape and position drive morphogenesis in epithelia and depend on the polarized nature of its constituent cells. The spectrin-based membrane skeleton is thought to be a key player in the establishment and/or maintenance of cell shape and polarity. We report that apical beta(Heavy)-spectrin (beta(H)), a terminal web protein that is also associated with the zonula adherens, is essential for normal epithelial morphogenesis of the Drosophila follicle cell epithelium during oogenesis. Elimination of beta(H) by the karst mutation prevents apical constriction of the follicle cells during mid-oogenesis, and is accompanied by a gross breakup of the zonula adherens. We also report that the integrity of the migratory border cell cluster, a group of anterior follicle cells that delaminates from the follicle epithelium, is disrupted. Elimination of beta(H) prevents the stable recruitment of alpha-spectrin to the apical domain, but does not result in a loss of apicobasal polarity, as would be predicted from current models describing the role of spectrin in the establishment of cell polarity. These results demonstrate a direct role for apical (alphabeta(H))(2)-spectrin in epithelial morphogenesis driven by apical contraction, and suggest that apical and basolateral spectrin do not play identical roles in the generation of apicobasal polarity.

Show MeSH
Related in: MedlinePlus