"Determination of the Mechanisms of Cytoplasmic Streaming" by Alex B. Keith
 

Masters Theses

Date of Award

12-2024

Degree Type

Thesis

Degree Name

Master of Science

Major

Biochemistry and Cellular and Molecular Biology

Major Professor

Andreas Nebenführ

Committee Members

Brad Binder, Elena Shpak

Abstract

Cytoplasmic streaming, or the movement of organelles, is a myosin-driven process discovered over two centuries ago. Myosins are evolutionarily conserved motor proteins that transport bound cargo along filaments. While it is known that cytoplasmic streaming is important for normal plant growth, the mechanism of how this process functions has yet to be identified. Currently there are three theories that describe the mechanism behind cytoplasmic streaming, termed Active, Passive, and Indirect models. The Active model states that myosins bind to individual cargo and carry them along actin filaments individually, while the Passive model states that myosins bind to some organelles, and others get moved by the stirring of the cytosol. The Indirect model states that myosins bind to the ER, which interacts with other organelles via linker proteins. By transporting the ER, the myosins are then, indirectly, transporting other organelles. To determine which theory is most accurate, constructs termed Boosters and Anchors were designed to either enhance myosin-organelle binding or anchor organelles to the microtubules, respectively, changing the organelles’ movement behavior. When quantified, Anchors were able to increase localization of targeted organelles to microtubules, showcasing that the constructs function as designed. Boosters and Anchors also functioned as expected on targeted organelles, with Boosters enhancing speeds and the percentage of linear movements while Anchors slowed speeds and decreased the percentage of linear movements. For the most part, non-targeted organelles were unaffected by the movements of targeted organelles. However, both Golgi stacks and peroxisomes seemed to be affected by Boosting-ER movement. Additionally, data showcases that mitochondria and peroxisomes have some sort of interaction, potentially related to hydrodynamic flow. Altogether, this data provides support for the Active model of organelle motility, based on non-targeted organelle motility being largely unaffected.

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