Date of Award
Summer 8-14-2020
Degree Type
Thesis
Degree Name
Master of Science in Integrative Biology (MSIB)
Department
Biology
Committee Chair/First Advisor
Anton Bryantsev
Major Professor
Anton Bryantsev
Second Committee Member
Susan Smith
Third Committee Member
Scott Nowak
Fourth Committee Member
Martin Hudson
Abstract
Muscle atrophy (MA) is a phenomenon of muscle mass loss due to accelerated protein degradation in muscle fibers. Some pathological conditions, such as chronic inflammation or cancer, induce accelerated MA, which complicates medical treatment, hampers recovery of fragile patients, and ultimately can be the cause of a patient’s death. To gain better control over MA, more information is required about the whole spectrum of genetic factors that can influence MA.
Drosophila provides an excellent platform for genetic screening, although it has somewhat limited utility for MA research since insect muscles lack the level of plasticity found in mammalian muscles. We adapted Drosophila flight muscles for a model of simulated MA, in which experimentally induced muscle actin knockdown causes concomitant degradation of actin-associated proteins, such as troponins and tropomyosins. We identified that proteins that are associated with thin filaments in the contractile apparatus are the ones that respond to actin loss most dramatically.
Using a collection of ‘readout proteins’ with different sensitivity to actin loss, we conducted a small-scale genetic screen, aiming to identify genes that affect protein clearance in actin-depleted flight muscles. We reasoned that these genes might be potent in regulating actual MA. Our screen has identified 20 genes of diverse functions, most of them not previously associated with MA.
We conducted a follow-up analysis for three factors uncovered by the screen: molecular chaperone Hsp22, actin regulator capt, and E3 ubiquitin ligase mib2. Genetic knockdown of each factor in actin-depleted flight muscles resulted in a retention of at least two out of four ‘readout proteins’ and various morphological phenotypes, such as size and number of protein aggregates and amount of polymerized actin. However, testing capt in in vivo, in developing pupa did not confirm its effect on developmentally regulated MA.
Overall, our model holds promise for identifying novel candidates that handle protein clearance from muscles, but findings obtained with this model must be confirmed by a thorough validation.