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Complete canthi removal reveals that forces from the amnioserosa alone are sufficient to drive dorsal closure in Drosophila.

Wells AR, Zou RS, Tulu US, Sokolow AC, Crawford JM, Edwards GS, Kiehart DP - Mol. Biol. Cell (2014)

Bottom Line: Canthi maintain purse string curvature (necessary for their dorsalward forces), and zipping at the canthi shortens leading edges, ensuring a continuous epithelium at closure completion.Dissection of one or both canthi resulted in tissue recoil and flattening of each purse string.How the embryo coordinates multiple, large forces (each of which is orders of magnitude greater than the net force) during native closure and is also resilient to multiple perturbations are key extant questions.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Duke University, Durham, NC 27708.

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Canthus removal on an embryo in midclosure results in gradual flattening of leading edges, no significant ventralward recoil, and near-native rates of closure after short lag phase. (A) Time-lapse confocal micrograph montage of an embryo ubiquitously expressing DE-cadherin-GFP. Both canthi were removed by laser incisions. t = 0 signifies the start of the first incision. Note the minimal ventralward recoil of leading edges near the incision sites for this embryo (between Ai and Aii; see Supplemental Movie S2 for its corresponding time-lapse video). (B) Montage of a native embryo expressing DE-cadherin-GFP at approximately the same time points as A (see Supplemental Movie S4 for its corresponding time-lapse video). (C) A canthus removal schematic representing a dorsal closure–staged embryo shown for reference (same as the schematic described in detail in Figure 1C). (D) Plot of height vs. time for the embryo in A at positions diagrammed in Ciii. The gray height curve represents the native embryo in B. (E) Traces of the leading edges with different color for each time point in the montage during closure of the embryo in A. This further highlights the lack of significant ventralward recoil of the leading edges after canthus removal. (F) Same display as E for the native embryo in B. Scale bar, 20 μm (Bv).
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Figure 2: Canthus removal on an embryo in midclosure results in gradual flattening of leading edges, no significant ventralward recoil, and near-native rates of closure after short lag phase. (A) Time-lapse confocal micrograph montage of an embryo ubiquitously expressing DE-cadherin-GFP. Both canthi were removed by laser incisions. t = 0 signifies the start of the first incision. Note the minimal ventralward recoil of leading edges near the incision sites for this embryo (between Ai and Aii; see Supplemental Movie S2 for its corresponding time-lapse video). (B) Montage of a native embryo expressing DE-cadherin-GFP at approximately the same time points as A (see Supplemental Movie S4 for its corresponding time-lapse video). (C) A canthus removal schematic representing a dorsal closure–staged embryo shown for reference (same as the schematic described in detail in Figure 1C). (D) Plot of height vs. time for the embryo in A at positions diagrammed in Ciii. The gray height curve represents the native embryo in B. (E) Traces of the leading edges with different color for each time point in the montage during closure of the embryo in A. This further highlights the lack of significant ventralward recoil of the leading edges after canthus removal. (F) Same display as E for the native embryo in B. Scale bar, 20 μm (Bv).

Mentions: Here we examine the combined roles of zipping and purse string curvature during dorsal closure with two novel laser protocols that dissect one or both canthi from the rest of the dorsal opening (Figures 1, A and B, and 2, A and B). The time course of the shape changes of the amnioserosa cells and the geometry of the leading edges were quantified. One key advantage for both protocols is the acute removal of one or both canthi, such that normal zipping and seam formation did not occur. A second key advantage is that the native curvature of the purse strings was not maintained after canthi removal. The purse strings recoil/shorten and flatten after the dissection of a canthus, reducing κ (and likely T), thus significantly reducing Tκ, the dorsalward component of the force due to the purse string. Remarkably, even when segments of the apposing purse strings were parallel to each other (and the dorsal midline), progress of the leading edge toward the dorsal midline was maintained at native or nearly native (unperturbed) rates until the end stages of closure, when pronounced slowing occurred before the completion of closure. Thus closure can proceed in the absence of purse string curvature, which we attribute to an increase in the force contribution from the amnioserosa. Quantitative analysis of amnioserosa cell shape shows changes in the length-to-width ratio of cells in approximately half of the dorsal opening closest to the removed canthus. In contrast, analysis of amnioserosa cell oscillations showed little or no change after canthus removal. Together our experiments confirm the robust nature of the dorsal closure process and support the existence of emergent properties that respond to alterations in purse string/actomyosin cable geometry to ensure successful closure.


Complete canthi removal reveals that forces from the amnioserosa alone are sufficient to drive dorsal closure in Drosophila.

Wells AR, Zou RS, Tulu US, Sokolow AC, Crawford JM, Edwards GS, Kiehart DP - Mol. Biol. Cell (2014)

Canthus removal on an embryo in midclosure results in gradual flattening of leading edges, no significant ventralward recoil, and near-native rates of closure after short lag phase. (A) Time-lapse confocal micrograph montage of an embryo ubiquitously expressing DE-cadherin-GFP. Both canthi were removed by laser incisions. t = 0 signifies the start of the first incision. Note the minimal ventralward recoil of leading edges near the incision sites for this embryo (between Ai and Aii; see Supplemental Movie S2 for its corresponding time-lapse video). (B) Montage of a native embryo expressing DE-cadherin-GFP at approximately the same time points as A (see Supplemental Movie S4 for its corresponding time-lapse video). (C) A canthus removal schematic representing a dorsal closure–staged embryo shown for reference (same as the schematic described in detail in Figure 1C). (D) Plot of height vs. time for the embryo in A at positions diagrammed in Ciii. The gray height curve represents the native embryo in B. (E) Traces of the leading edges with different color for each time point in the montage during closure of the embryo in A. This further highlights the lack of significant ventralward recoil of the leading edges after canthus removal. (F) Same display as E for the native embryo in B. Scale bar, 20 μm (Bv).
© Copyright Policy - creative-commons
Related In: Results  -  Collection

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Figure 2: Canthus removal on an embryo in midclosure results in gradual flattening of leading edges, no significant ventralward recoil, and near-native rates of closure after short lag phase. (A) Time-lapse confocal micrograph montage of an embryo ubiquitously expressing DE-cadherin-GFP. Both canthi were removed by laser incisions. t = 0 signifies the start of the first incision. Note the minimal ventralward recoil of leading edges near the incision sites for this embryo (between Ai and Aii; see Supplemental Movie S2 for its corresponding time-lapse video). (B) Montage of a native embryo expressing DE-cadherin-GFP at approximately the same time points as A (see Supplemental Movie S4 for its corresponding time-lapse video). (C) A canthus removal schematic representing a dorsal closure–staged embryo shown for reference (same as the schematic described in detail in Figure 1C). (D) Plot of height vs. time for the embryo in A at positions diagrammed in Ciii. The gray height curve represents the native embryo in B. (E) Traces of the leading edges with different color for each time point in the montage during closure of the embryo in A. This further highlights the lack of significant ventralward recoil of the leading edges after canthus removal. (F) Same display as E for the native embryo in B. Scale bar, 20 μm (Bv).
Mentions: Here we examine the combined roles of zipping and purse string curvature during dorsal closure with two novel laser protocols that dissect one or both canthi from the rest of the dorsal opening (Figures 1, A and B, and 2, A and B). The time course of the shape changes of the amnioserosa cells and the geometry of the leading edges were quantified. One key advantage for both protocols is the acute removal of one or both canthi, such that normal zipping and seam formation did not occur. A second key advantage is that the native curvature of the purse strings was not maintained after canthi removal. The purse strings recoil/shorten and flatten after the dissection of a canthus, reducing κ (and likely T), thus significantly reducing Tκ, the dorsalward component of the force due to the purse string. Remarkably, even when segments of the apposing purse strings were parallel to each other (and the dorsal midline), progress of the leading edge toward the dorsal midline was maintained at native or nearly native (unperturbed) rates until the end stages of closure, when pronounced slowing occurred before the completion of closure. Thus closure can proceed in the absence of purse string curvature, which we attribute to an increase in the force contribution from the amnioserosa. Quantitative analysis of amnioserosa cell shape shows changes in the length-to-width ratio of cells in approximately half of the dorsal opening closest to the removed canthus. In contrast, analysis of amnioserosa cell oscillations showed little or no change after canthus removal. Together our experiments confirm the robust nature of the dorsal closure process and support the existence of emergent properties that respond to alterations in purse string/actomyosin cable geometry to ensure successful closure.

Bottom Line: Canthi maintain purse string curvature (necessary for their dorsalward forces), and zipping at the canthi shortens leading edges, ensuring a continuous epithelium at closure completion.Dissection of one or both canthi resulted in tissue recoil and flattening of each purse string.How the embryo coordinates multiple, large forces (each of which is orders of magnitude greater than the net force) during native closure and is also resilient to multiple perturbations are key extant questions.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Duke University, Durham, NC 27708.

Show MeSH
Related in: MedlinePlus