Date of Award

2020

Document Type

Dissertation

Degree Name

Ph.D.

Department

Biological Sciences

First Advisor

James Todd Blankenship

Second Advisor

Joseph Angleson

Third Advisor

Dinah Loerke

Fourth Advisor

Schuyler van Engelenburg

Keywords

Actin cap, Arp2/3, Drosophila, Embryogenesis, Furrow ingression

Abstract

Drosophila embryogenesis starts with a single nucleus undergo 13 rounds of nuclear divisions called syncytial cycles. Staring at cycle 10 when nuclei migrate to the surface of the embryo, massive and dynamic cortical actin structures and cleavage furrow formations occur. How actin regulators coordinate into an organized network directing three-dimension actin structures in the developing organisms is an unsolved question. Here, I present an in-depth characterization of actin cap dynamics: the actin caps go through expansion, stabilization, elongation and fragmentation phases in each cycle. Arp2/3 is the major contributor to actin cap formation. The functions of 7 different actin and Arp2/3 regulators provide distinct but combinatorial activities. Specifically, DPod1 is the major contributor for actin intensities, Cortactin is required for cortical cap growth and size maintenance, and Coronin functions in both growth and intensity and is also required for Cortactin peripheral translocation. Interestingly, the recovery of cortical actin is faster when regulator disruption, suggesting a potential deep competition of actin regulators for a limited free globular actin (G-actin) pool. Using an ectopic relocation strategy, I measure and show in vivo Arp2/3 recruitment abilities by different regulators. My results suggest how the interplay of multiple actin regulators orchestrate organized and dynamic actin structures.

Besides the cortical actin dynamics, Drosophila syncytial cycles also provide a nice model for investigation of how progressive lengthening of cleavage furrow from cycle 10 to 13 is dynamically regulated. Here, I show that the deepening in furrow dimensions during syncytial cycles is largely due to the introduction of a new, rapid ingression phase (Ingression II). Blocking the midblastula transition (MBT) causes the absence of Ingression II, and consequently reduces furrow dimensions. The analysis of compound chromosomes that produce chromosomal aneuploidies suggests that multiple loci on the X, II, and III chromosomes contribute to the production of differentially-dimensioned furrows. I show that the nullo gene product is the X-chromosomal contributor to furrow lengthening. Additionally, the checkpoint proteins are required but not strictly deterministic for furrow lengthening. The results also indicate that the furrow dynamics during cellularization (cycle 14) are a continuation of dynamics established during the syncytial cycles.

Publication Statement

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

Provenance

Received from ProQuest

Rights holder

Yi Xie

File size

116 p.

File format

application/pdf

Language

en

Discipline

Biology, Developmental biology, Cellular biology

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