Leveraging Drosophila to identify novel and conserved regulators of cardiomyocyte polyploidy

ABSTRACT: During the transition to adolescence, mammalian cardiomyocytes switch from a proliferative phase to a growth phase, primarily achieving expansion through whole genome duplication, also known as polyploidization. Unlike most polyploid tissues, I have found that the Drosophila heart has rigid ploidy limits crucial for optimal function. My postdoctoral work has revealed that the Drosophila cardiac organ has a chamber-specific asymmetry to cardiomyocyte polyploidization, which I found is also conserved in humans. Altering this chamber- specific asymmetry significantly impacts cardiac function in Drosophila, resembling human cardiomyopathies. To identify conserved regulators of cardiomyocyte polyploidization, I used reverse genetics in Drosophila to interrogate human cardiac chamber-specific gene expression differences. This genetic screen, as well as subsequent screens described herein, identified conserved organ-specific and novel cardiac- specific genes important for heart tissue ploidy regulation. This proposal builds on my successful screen to reveal new molecular mechanisms of cardiac ploidy control. Utilizing Drosophila genetics, Optical Coherent Tomography, immunofluorescence imaging and mammalian cardiomyocytes, I propose the following aims during the K99/R00 phase: AIM1: Identify the mechanism of cardiac-specific ploidy regulation by COX7A (K99). I identified cytochrome c oxidase subunit 7A (COX7A) as a heart-specific ploidy regulator. My hypothesis is that COX7A functions as a specific regulator of cardiomyocyte polyploidization through repressing mitochondrial production. AIM2: Identify the mechanism of cardiac-specific ploidy regulation by DZfand (K99/R00). I identified the Zinc Finger Protein DZfand as a novel cardiac-specific ploidy regulator. My hypothesis is that DZfand functions as a transcriptional regulator to negatively regulate cardiomyocyte polyploidization. AIM3: Identify cardiac-specific function of Goliath ubiquitin ligases and other HF-linked GWAS genes in heart diseases (R00). I found an enrichment of ubiquitin ligases in publicly available GWAS data for heart failure (HF), which prompted me to conduct an Optical Coherence Tomography (OCT)-based reverse genetic screen of Drosophila ubiquitin ligase genes. I identified that Goliath (gol/RFN150) ubiquitin ligases regulated cardiac function. Hypothesis: Goliath ubiquitin ligases regulate cardiomyocyte polyploidization during heart failure (HF). Building on the success of the OCT-based screen, I will expand this approach to screen for GWAS- identified genes linked to HF in my independent phase. My work to identify novel cardiac ploidy regulators using accessible Drosophila genetics is unique and crucial for understanding heart diseases, given that cardiovascular diseases rank as the leading global cause of death. To successfully achieve these aims, I have designed a training plan with my advisor, Dr. Don Fox, to acquire the necessary skills for transitioning to an independent research role. Additionally, guidance from my advisory committee and collaborators will further enhance my conceptual, technical, and professional abilities, facilitating this transition.