Nuclear-mitochondrial mismatch in mitochondrial function and disease

Georgia Southern University Research & Service Foundation Inc. received a $507,544 Project Grant award dated August 25, 2025, from the National Institute of General Medical Sciences (NIGMS) under the Biomedical Research and Research Training program (CFDA 93.859) to conduct fundamental research on nuclear-mitochondrial genetic mismatches and their impact on mitochondrial dysfunction. The three-year project, concluding August 24, 2028, utilizes Nasonia wasps as a genetic model system to investigate how mutations causing mismatches between nuclear-encoded and mitochondrial-encoded genes lead to mitochondrial dysfunction and disease. The research employs diagnostic assays equivalent to those used in human mitochondrial disease diagnosis, specifically analyzing oxidative phosphorylation (OXPHOS) pathway enzyme function and overall mitochondrial respiration rates in isolated mitochondria from interspecific hybrid wasp strains.

The project addresses critical knowledge gaps regarding the genetic underpinnings of mitochondrial diseases—among the most common genetic disorders in humans—by analyzing how nuclear-mitochondrial genetic incompatibilities negatively impact mitochondrial function and organismal health. Research deliverables include detailed functional analyses of mitochondrial enzyme complexes and respiration rates in hybrid strains exhibiting severe phenotypic effects, thereby establishing the mechanistic basis for how genetic mismatches compromise mitochondrial performance and contributing foundational knowledge applicable to understanding human mitochondrial disease pathology.

Abstract

Mitochondria are critical organelles that integrate many aspects of cellular function, most notably the generation of the vast majority of cellular energy via the oxidative phosphorylation (oxphos) pathway. Mitochondria require the coordination of their own small genome of 37 genes with more than 1,000 nuclear-encoded genes in order to function properly, resulting in a close match between nuclear and mitochondrial-encoded genes. Mitochondrial diseases, among the most common genetic disorders in humans, are the result of mutations causing a mismatch between these nuclear and mitochondrial-encoded genes that lead to mitochondrial dysfunction. Despite the importance of mitochondria in the cell and the impact of mitochondrial dysfunction on human health, our understanding of the specific genetic underpinnings of mitochondrial dysfunction remains limited. The proposed research aims to address these knowledge gaps by utilizing a highly tractable genetic model system, nasonia wasps, to determine how mutations that result in a nuclear-mitochondrial genetic mismatch negatively impact mitochondrial function and organismal health. These wasps have simple genetics, haploid males and diploid females, that make them ideal for determining the genetic basis of mitochondrial dysfunction. We propose to analyze mitochondrial function using assays that are used to diagnose mitochondrial disease in humans, specifically the function of the individual enzymes of the oxphos pathway as well as overall mitochondrial respiration rate in mitochondria isolated from interspecific hybrid strains of these wasps. Specific aim 1 will focus on analyzing hybrids that have previously been shown to suffer from ~98% male juvenile mortality when they have a nuclear allele at a single locus that is mismatched with their mitochondria, as well as analyzing hybrids produced using a strain of wasps that has been shown to significantly rescue this mortality due to having the nuclear allele that matches the mitochondria. Using these two hybrid types, this aim will measure the function of mitochondria from haploid male wasp larvae before they DIE in order to directly test the mismatched allele's impact on mitochondrial function, as well as in diploid adult females that have been shown to suffer less mortality, mirroring the recessive nature of most human mitochondrial diseases. Specific aim 2 will focus on identifying additional loci underlying hybrid mortality associated with mitochondrial mismatch using genome-wide sequencing of very large pools of surviving adults. Each mitochondrially-mismatched loci will then be isolated in a separate wasp strain with an otherwise mitochondria-matching nuclear genome via marker-assisted introgression, and these strains will be assayed for mortality and mitochondrial function to determine the impact of each mismatched locus on mitochondrial and organismal health. This project will provide valuable insights into the specific impacts of mutations on mitochondrial function as well as our basic understanding of the genetic underpinnings of mitochondrial function in general. Moreover, this project will provide strong research experiences for students engaged in IT while strengthening the research environment for future students.