Author(s): Syrus Miner, Troy Webb
Mentor(s): Hung Yu Shih, Yu-Chien Liu
Institution UTech
4H Leukodystrophy is a rare neurodegenerative disorder characterized by hypomyelination, hypodontia, and hypogonadotropic hypogonadism—the “4 H’s.” Mutations in the POLR3 genes, which encodes a polymerase essential for transcribing many housekeeping genes, are common in patients. Polr3b, the second-largest subunit of this polymerase, plays a critical role in this process. Two current mouse models using the Cre-lox system have provided valuable insights into the disorder. One model revealed impaired cellular proliferation in intestinal tissues, while the other highlighted symptoms such as hypomyelination, ataxia, and craniofacial deformities. However, both fail to capture the full disease progression. While they model early oligodendrocyte precursor cell (OPC) defects, particularly a failure in proliferation, they do not replicate later stages of the disease, such as neurodegeneration. Incomplete recombination in OPCs limits the severity of the phenotype, as non-recombined cells likely compensate for the defects in recombined cells. To address this limitation, we propose developing a zebrafish (Danio rerio) model by knocking down Polr3b at the single-cell stage using morpholino technologies. Zebrafish are well-suited for this research due to their genetic similarity to humans, transparent embryos that allow for non-invasive observation, and rapid development. The goal of this model is to investigate the cellular and molecular mechanisms underlying 4H leukodystrophy, with a focus on the impact of Polr3b disruption in oligodendrocyte development and myelination. This model will enable us to better understand the developmental defects associated with 4H and explore potential therapeutic interventions. We expect our zebrafish model to display phenotypes similar to those seen in humans, including hypomyelination in the midbrain and forebrain, craniofacial abnormalities, and developmental defects associated with oligodendrocyte dysfunction. Additionally, we anticipate reduced cellular proliferation in neural tissues, leading to fewer oligodendrocyte precursor cells during critical developmental periods, which may contribute to the neurodevelopmental issues in 4H Leukodystrophy. This project aims to enhance understanding of 4H pathogenesis and inform future therapeutic strategies.