Why Do Mutant Genes in Glial Cells Increase Risk of Febrile Seizures?

Sarah Iannone ’25 spent her summer researching two genes in glia and how they affect neuronal excitability in fruit flies.

For animals to respond properly to environmental changes, such as temperature fluctuations, their nervous systems must be regulating correctly. It’s a biological function that is vital to survival. The question of why some cannot continue managing these necessary bodily functions, possibly leading to the onset of high fever-induced febrile seizures, is one that Sarah Iannone ’25 has spent her summer researching with Alexis Hill, assistant professor of biology. Iannone is one of dozens of College of the Holy Cross students who participated in the College's Charles S. Weiss Summer Research Program. Her research project builds off previous student research undertaken in Hill’s lab and whose findings were published in the scientific journal PLOS Genetics in 2019.

What should people know about your research?

While most people can maintain internal biological stability (homeostasis) even at increased temperatures, some humans with mutations in specific nervous system genes can experience febrile seizures when they have a high fever. The goal of my summer research is to understand how glial cells – small cells that support nerve cells – contribute to neuronal homeostasis during changes in the environment, such as heat. People in the neuroscience community lack a full understanding of how glial cells interact with environmental stressors. Results from this project can provide useful information for understanding how glial cells regulate neuronal homeostasis. 

Tell us more about your research.

I’m studying neuronal excitability, an important component of how the nervous system controls muscles and movement, to understand how the nervous system adapts to changes in the environment in a homeostatic manner and continues to control critical bodily functions and behaviors. Drosophila melanogaster – a type of fruit fly used in scientific research – is ideal to study the genes involved in this process because it is relatively easy to manipulate these specific genes in these flies. 

Not many people in the neuroscience community have focused on how subtypes of glia affect neuronal excitability. Assistant Professor Hill has identified two genes in Drosophila that affect nervous system susceptibility to environmental stress due to functions in a glial cell subtype called EGN (neuropile ensheathing glia). These two genes are the seizure gene known as sei and the sodium/potassium/chloride transporter gene known as ncc69. Her previous research has shown inactivating (knocking down) the sei gene in EGN increases susceptibility to heat-induced seizure and paralysis, and doing the same to the ncc69 gene in EGN increases susceptibility to bang-induced seizure and paralysis. 

The first part of my research this summer was to repeat an experiment from Assistant Professor Hill’s neurobiology lab class, in which ncc69 was inactivated in all glial cells or specifically EGN, in order to verify that the standard protocol leads to replicable results. Then, I developed a new protocol that will enable me to test if additional manipulations in EGN lead to increased seizure susceptibility, beyond knocking down ncc69 alone.

In a second part of my research, I developed assays – experimental protocols– involving the sei gene that focused on fruit fly larvae. First, I replicated data that has already been published using controls and sei gene mutant larvae as a way of verifying that the assays are reproducible. I expect to see sei gene mutant larvae spending less time exhibiting normal locomotion behavior and more time exhibiting seizure-like whipping behavior. Published research has shown that the knockdown of the sei gene in all glia or EGN using adult heat assay increases seizure susceptibility, therefore my research this summer tested if the same is true using larval assays. I am currently analyzing the results of these experiments. 

Why did you want to develop assays that focus on fly larvae?  

We wanted to develop assays that focus on larvae because our research goal is to compare the impact of EGN sei and ncc69 genes on motor behavior and neural excitability under baseline and stress conditions. It is easier to use these techniques in larvae than in adult flies.  

Why did you decide to research the function of the ncc69 gene, in addition to the sei gene?

The ncc69 gene is one of the many genes that affect nervous system susceptibility to environmental stress. ncc69 is a sodium/potassium/chloride symporter, whose knockdown (inactivation) in all glia or specifically EGN increases susceptibility to bang-induced seizure and paralysis in Drosophila. In adult Drosophila, EGN may support adaptability of the nervous system through their function as phagocytes –cells that can remove dead cells or portions of cells. Based on Assistant Professor Hill’s data and other literature, we hypothesize that phagocytic functions of EGN glia may be critical for nervous system homeostasis during environmental stress.

Do you intend to continue with this research after the summer? If so, how?

In the fall, I hope to test the hypothesis that the phagocytic function of EGN glial cells might be critical for homeostasis during environmental stress. I’ll use the protocol I developed to test whether the seizure susceptibility phenotypes of ncc69 EGN knockdown are exacerbated when combined with the knockdown of phagocytic pathway genes.