Author ORCID Identifier

https://orcid.org/0000-0001-8722-6253

Date of Award

Fall 11-2022

Document Type

Thesis (Ph.D.)

Department or Program

Biological Sciences

First Advisor

Bing He

Second Advisor

James B. Moseley

Third Advisor

Magdalena Bezanilla

Abstract

Actomyosin contractility plays an important role at both the cell and tissue level during developments. In this study, we developed an optogenetic tool that can acutely inhibit actomyosin contractility by targeting its main activator Rho1. This optogenetic tool can achieve myosin inhibition within one minute and thus enable further dissection of actomyosin function in development. In my first two projects, I used Drosophila mesoderm invagination (also known as ventral furrow formation) as a model to study epithelial folding, a fundamental mechanism for constructing complex 3D tissues. Apical constriction mediated by actomyosin contractility is a common mechanism for epithelial folding. However, it is unclear how contractile forces near the apical surface of the cell sheet drive out-of-the-plane bending of the sheet. Using the optogenetic tool, we found that actomyosin is necessary for initiating ventral furrow formation but is dispensable for the subsequent furrow invagination. This binary tissue response suggests that the mesoderm is mechanically bistable. Combining computer modeling, quantitative live imaging and laser-mediated tissue manipulation, we found that this mechanical bistability is induced by a compression from the surrounding ectoderm, which facilitates mesoderm invagination by triggering epithelial buckling. Together, these findings provide important insights into the mechanical mechanism of epithelial folding induced by apical constriction. In my third project, I focused on the role of actomyosin in regulating adherens junctions during Drosophila germband extension, a body axis elongation process. Rho1-mediated actomyosin has been shown to antagonize E-cadherin, the core component of adherens junctions, to facilitate tissue elongation. Unexpectedly, we found that Rho1 inhibition results in rapid fragmentation of adherens junctions. Combining drug injection and mutant analysis, we further showed that adherens junction fragmentation is due to loss of junctional myosin. These results revealed, for the first time to our knowledge, that Rho1 has two distinct roles in regulating adherens junctions under the same developmental context. It also raises the possibility that Rho1 has a dosage dependent effect on E-cadherin organization. Taken together, by developing a highly effective optogenetic tool, my work extended the field’s knowledge about the function of Rho1-dependent actomyosin contractility and opened the door for new directions for future research avenue.

Original Citation

Hanqing Guo, Michael Swan, Bing He (2022) Optogenetic inhibition of actomyosin reveals mechanical bistability of the mesoderm epithelium during Drosophila mesoderm invagination. eLife 11:e69082 https://doi.org/10.7554/eLife.69082

Hanqing Guo, Shicheng Huang and Bing He (2022) Evidence for a Role of the Lateral Ectoderm in Drosophila Mesoderm Invagination. Front. Cell Dev. Biol. 10:867438. doi: 10.3389/fcell.2022.867438

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