Evaluating the Effect of p.T46I Mutation in H3.3 on Mouse Development



Assistant Professor of Pediatrics and Human Genetics

Project Summary

This summer, I had the pleasure of working in Dr. Elizabeth Bhoj’s laboratory at the Leonard and Madlyn Abramson Pediatric Research Center at CHOP alongside postdoctoral fellow Laura Bryant. The Bhoj lab studies the pathological mechanisms of novel neurogenetic disorders in children and recently identified heterozygous missense mutations in the histone variant H3.3 that cause a novel neurodevelopmental and neurodegenerative syndrome. My project focused on a specific missense mutation in one of the genes encoding H3.3 which results in a change in amino acid 46 from threonine (T) to isoleucine (I). This mutation was seen in four unrelated patients, making it the most common mutation in our cohort. We created a mouse model of this disease that reflects this human heterozygous germline mutation of p.T46I in gene H3F3A. 
My primary responsibility was evaluating the ratio of heterozygous mice to wildtype mice in the offspring of mouse crosses between a male heterozygous for H3.3p.T46I and a wildtype female. Genotyping the mouse pups to determine if they are wildtype or heterozygous for the H3.3p.T46I mutation is important because a decrease in the number of heterozygous pups compared to wildtype pups indicates that this mutation impacts the viability of either the embryos or young pups. Additionally, it allows us to design appropriate developmental and behavioral tests comparing the heterozygous mice to the wildtype mice and determine if the mice recapitulate the patient phenotype, which includes developmental delay, cognitive deficits, and limited locomotion, among others. 
The ultimate goal of the project is to better understand the developmental ramification of this specific mutation and novel disorder. Then, a targeted therapy trial in the mouse line, and eventually for the affected children, can be performed. 
Throughout the summer, I also had the opportunity to attend pediatric genetics clinics with Dr. Bhoj and meet a variety of affected children. I was able to see the intersection of laboratory science and clinical medicine and was given insight into a medical specialty I was previously unaware of. 
Participating in journal clubs with the lab staff offered me valuable experience in reading, interpreting, and intellectually discussing research papers. This has exposed me to the application of many basic biochemical processes and will complement my general science courses in college.
In lab, beyond learning new techniques such as polymerase chain reaction, genotyping, and molecular cloning, I learned to think deeper when troubleshooting was needed after experimental results were unclear or absent. There is not one avenue to results in science; there is almost always another technique that can be used to bypass issues.  
I am looking forward to continuing this project in Dr. Bhoj’s lab during the academic year!