Date of Award

2021

Document Type

Dissertation

Degree Name

Ph.D.

Department

Biological Sciences

First Advisor

James Todd Blankenship

Second Advisor

Cedric Asensio

Third Advisor

Dinah Loerke

Fourth Advisor

Joseph K. Angleson

Keywords

Cytoskeleton, Development, Trafficking

Abstract

Force generation in epithelial tissues is often pulsatile, with actomyosin networks generating high-tension contractile forces at the cell cortex before cyclically disassembling. This pulsed nature of cytoskeletal forces implies that there must be cellular processes to extract unidirectional changes that drive processive transformations in cell shape. During Drosophila melanogastergastrulation, the invagination of the prospective mesoderm is driven by the pulsed constriction of apical surfaces. Here, we address the mechanisms by which the irreversibility of pulsed events is achieved while also permitting uniform epithelial behaviors to emerge. We use MSD-based analyses to identify contractile steps and find that when a trafficking pathway initiated by Sbf is disrupted, contractile steps become reversible. Sbf localizes to tubular, apical surfaces and associates with Rab35, where it promotes Rab GTP exchange. Interestingly, when Sbf/Rab35 function is compromised, the apical plasma membrane becomes deeply convoluted, and nonuniform cell behaviors begin to emerge. Consistent with this, Sbf/Rab35 appears to prefigure and organize the apical surface for efficient Myosin function. We also show that Sbf/Rab35/CME directs the plasma membrane to Rab11 endosomes through a dynamic interaction with Rab5 endosomes. Finally, we find plasma membrane lipid cues in the form of PtdIns(3,4,5)P3 are a critical determinant for Sbf/Rab35 ratcheting engagement. These results suggest that periodic ratcheting events shift excess membrane from cell apices into endosomal pathways to permit reshaping of actomyosin networks and the apical surface.

Publication Statement

Copyright is held by the author. User is responsible for all copyright compliance.

Provenance

Received from ProQuest

Rights holder

Hui Miao

File size

95 pgs

File format

application/pdf

Language

en

Discipline

Molecular biology, Developmental biology

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