PROJECT SUMMARY
Post-transcriptional regulation of gene expression is critical for proper neuronal development and function. Many
of these highly coordinated post-transcriptional regulatory events are mediated by an evolutionarily conserved
and ubiquitously-expressed RNA processing complex, the RNA exosome. The RNA exosome is an essential 10-
subunit complex that has dual function in precise processing and quality-control driven degradation of a variety
of cellular RNAs. Recent clinical reports have linked autosomal recessive missense mutations in the genes
encoding structural subunits of the RNA exosome to distinct tissue-specific disorders with shared neurological
features. Significantly, these mutations encoding single amino acid substitutions cause a range of clinical
manifestations that do not correlate with the type of structural gene that is mutated. For example, disease-linked
mutations in RNA exosome subunit genes: EXOSC3 and EXOSC9 cause distinct subtypes of a devastating
neurodevelopmental disorder, Pontocerebellar Hypoplasia Type 1B (PCH1B) and Type 1D (PCH1D),
respectively. In contrast, mutations in RNA exosome subunit gene EXOSC2 cause a novel syndrome, SHRF
(Short stature, Hearing loss, Retinitis pigmentosa, and distinctive Facies), as well as mild cerebellar atrophy.
Taken together, these observations both indicate tissue-specific function for the RNA exosome and an enhanced
requirement for the complex in neurodevelopment. The tissue-specific defects caused by mutations in genes
encoding the RNA exosome are challenging to understand given the limited analysis of RNA exosome disease-
linked variants in any multicellular organism in vivo. Towards understanding the biological mechanism of RNA
exosome-linked neuronal dysfunction, my studies will focus on systematically investigating and comparing the
cell type/tissue-specificity of pathogenic variants in distinct RNA exosome subunits in the fly brain. Thus, I have
engineered flies modeling pathogenic mutations in RNA exosome Cap subunit genes: EXOSC2 (fly Rrp4),
EXOSC3 (fly Rrp40), and Core subunit gene EXOSC9 (fly Rrp45) via CRISPR/Cas9. Utilizing a Drosophila model
of RNA exosome-linked neurodevelopmental disease, I will test the hypothesis that subunits of the RNA
exosome mediate critical, yet distinct activities of the RNA exosome in post-transcriptional regulation in cells of
the nervous system in vivo. My preliminary data show that pathogenic variants in flies modeling RNA exosome-
linked disease genotypes are viable and produce a spectrum of phenotypes, thus providing an in vivo biological
venue to investigate the molecular basis for such disease. Thus, I will study the in vivo biological function of the
RNA exosome in cells of the nervous system through the following complementary aims: 1) Define the molecular
and cellular consequences of pathogenic variants in RNA exosome subunits; and 2) Examine how pathogenic
variants in the RNA exosome affect fly brain mushroom body morphology and function. Taken together, this
comparative analysis will provide insight into both tissue-specific function of the RNA exosome and the functional
consequences of disease-linked amino acid changes in vivo, which is critical to understand disease etiology.
