Biology subjects

Morton, D. J.

Publications and source records attributed to Morton, D. J..

5 recordsLinked to original sources

bioRxiv2026

Tissue-specific consequences of impaired RNA surveillance converge on mitochondrial homeostasis

RNA surveillance pathways maintain transcriptome integrity by eliminating aberrant, excess, and non-functional RNAs, yet it remains unclear whether distinct tissues exhibit equivalent requirements for RNA quality control. Here, we investigated the tissue-specific consequences of impaired RNA surveillance using a Drosophila allelic series of the RNA exosome subunit Rrp40. Comparative transcriptomic analyses revealed that neuronal-enriched head tissue and muscle-enriched thorax tissue exhibit largely distinct molecular programs following reduced RNA exosome activity despite disruption of the same RNA surveillance machinery. Antisense RNAs emerged as particularly sensitive targets of RNA exosome dysfunction, accumulating preferentially in neuronal tissue and largely independent of changes in overlapping sense host transcripts, indicating enhanced requirements for RNA-level quality control within the nervous system. Although tissue-specific transcriptomic alterations diverged substantially, multiple analyses converged on mitochondrial homeostasis as a shared vulnerability. Reduced RNA exosome activity was associated with widespread dysregulation of nuclear-encoded mitochondrial genes, mitochondrial dynamics pathways, and mitochondrial RNA regulatory programs, accompanied by progressive defects in mitochondrial organization, membrane potential, and ATP production. Mitochondrial dysfunction was further associated with activation of proteostatic stress pathways, including p62 accumulation and increased ubiquitination. Together, these findings demonstrate that tissue context shapes the molecular consequences of impaired RNA surveillance while revealing mitochondrial homeostasis as a convergent vulnerability arising from transcriptome instability. More broadly, our findings suggest that distinct tissue-specific defects in RNA regulation converge on common cellular vulnerabilities that ultimately govern tissue homeostasis.

molecular biology↗

bioRxiv2026

RNA exosome-mediated RNA surveillance governs developmental timing in the human cerebellum

Defects in RNA metabolism are a defining feature of neurodevelopmental disease, yet how RNA decay pathways contribute to human brain development remains poorly understood. Mutations in ubiquitously expressed RNA surveillance factors often cause highly tissue-selective disease, highlighting a central paradox in human biology. The RNA exosome is a conserved ribonuclease complex traditionally viewed as a housekeeping machine for RNA turnover, yet recessive mutations in genes encoding structural subunits of the complex disproportionately cause neurological disease, suggesting an instructive role in nervous system development. Here, we show that the RNA exosome regulates the temporal progression of gene expression programs during human cerebellar differentiation. Using CRISPR-engineered human cerebellar organoids modeling EXOSC3 variants, we find that RNA exosome dysfunction does not broadly alter transcript abundance, but instead disrupts transitions between developmental states. Mutant organoids exhibit incomplete and mis-timed resolution of early transcriptional programs, altered lineage specificity, and impaired coordination of maturation-associated gene expression programs, with pronounced effects in neuronal lineages, particularly Purkinje cells and rhombic lip-derivatives. These defects are accompanied by disorganized laminar architecture and reduced coordination of neuronal activity, despite preserved intrinsic excitability. Together, our findings establish RNA surveillance as a key regulator of developmental timing, lineage fidelity, and neurodevelopmental disease.

molecular biology↗

bioRxiv2024

The RNA exosome maintains cellular RNA homeostasis by controlling transcript abundance in the brain

Intracellular ribonucleases (RNases) are essential in all aspects of RNA metabolism, including maintaining accurate RNA levels. Inherited mutations in genes encoding ubiquitous RNases are associated with human diseases, primarily affecting the nervous system. Recessive mutations in genes encoding an evolutionarily conserved RNase complex, the RNA exosome, lead to syndromic neurodevelopmental disorders characterized by progressive neurodegeneration, such as Pontocerebellar Hypoplasia Type 1b (PCH1b). We establish a CRISPR/Cas9-engineered Drosophila model of PCH1b to study cell-type-specific post-transcriptional regulatory functions of the nuclear RNA exosome complex within fly head tissue. Here, we report that pathogenic RNA exosome mutations alter activity of the complex, causing widespread dysregulation of brain-enriched cellular transcriptomes, including rRNA processing defects--resulting in tissue-specific, progressive neurodegenerative effects in flies. These findings provide a comprehensive understanding of RNA exosome function within a developed animal brain and underscore the critical role of post-transcriptional regulatory machinery in maintaining cellular RNA homeostasis within the brain.

molecular biology↗

bioRxiv2020

The Nab2 RNA binding protein promotes sex-specific splicing of Sex lethal in Drosophila neuronal tissue

The Drosophila polyadenosine RNA binding protein Nab2, which is orthologous to a human protein lost in a form of inherited intellectual disability, controls axon projection, locomotion, and memory. Here we define an unexpectedly specific role for Nab2 in regulating splicing of [~]150 exons/introns in the head transcriptome and link the most prominent of these, female retention of a male-specific exon in the sex determination factor Sex-lethal (Sxl), to a role in m6A-dependent mRNA splicing. Genetic evidence indicates that aberrant Sxl splicing underlies multiple phenotypes in Nab2 mutant females. At a molecular level, Nab2 associates with Sxl pre-mRNA and ensures proper female-specific splicing by preventing m6A hypermethylation by Mettl3 methyltransferase. Consistent with these results, reducing Mettl3 expression rescues developmental, behavioral and neuroanatomical phenotypes in Nab2 mutants. Overall these data identify Nab2 as a required regulator of m6A-regulated Sxl splicing and imply a broader link between Nab2 and Mettl3-regulated brain RNAs.

developmental biology↗

bioRxiv2019

A Drosophila Model of Pontocerebellar Hypoplasia Reveals a Critical Role for the RNA Exosome in Neurons

The RNA exosome is an evolutionarily-conserved ribonuclease complex critically important for precise processing and/or complete degradation of a variety of cellular RNAs. The recent discovery that mutations in genes encoding structural RNA exosome subunits cause tissue-specific diseases makes defining the role of this complex within specific tissues critically important. Mutations in the RNA exosome component 3 (EXOSC3) gene cause Pontocerebellar Hypoplasia Type 1b (PCH1b), an autosomal recessive neurologic disorder. The majority of disease-linked mutations are missense mutations that alter evolutionarily-conserved regions of EXOSC3. The tissue-specific defects caused by these amino acid changes in EXOSC3 are challenging to understand based on current models of RNA exosome function with only limited analysis of the complex in any multicellular model in vivo. The goal of this study is to provide insight into how mutations in EXOSC3 impact the function of the RNA exosome. To assess the tissue-specific roles and requirements for the Drosophila ortholog of EXOSC3 termed Rrp40, we utilized tissue-specific RNAi drivers. Depletion of Rrp40 in different tissues reveals a general requirement for Rrp40 in the development of many tissues including the brain, but also highlight an agedependent requirement for Rrp40 in neurons. To assess the functional consequences of the specific amino acid substitutions in EXOSC3 that cause PCH1b, we used CRISPR/Cas9 gene editing technology to generate flies that model this RNA exosome-linked disease. These flies show reduced viability; however, the surviving animals exhibit a spectrum of behavioral and morphological phenotypes. RNA-seq analysis of these Drosophila Rrp40 mutants reveals increases in the steady-state levels of specific mRNAs and ncRNAs, some of which are central to neuronal function. In particular, Arc1 mRNA, which encodes a key regulator of synaptic plasticity, is increased in the Drosophila Rrp40 mutants. Taken together, this study defines a requirement for the RNA exosome in specific tissues/cell types and provides insight into how defects in RNA exosome function caused by specific amino acid substitutions that occur in PCH1b can contribute to neuronal dysfunction. Author SummaryPontocerebellar Hypoplasia Type 1b (PCH1b) is a devastating genetic neurological disorder that preferentially affects specific regions of the brain. Typically, children born with PCH1b have structural defects in regions of the brain including those associated with key autonomic functions. Currently, there is no cure or treatment for the disease. PCH1b is caused by mutations in the RNA exosome component 3 (EXOSC3) gene, which encodes a structural component of the ubiquitous and essential multi-subunit RNA exosome complex. The RNA exosome is critical for both precise processing and turnover of multiple classes of RNAs. To elucidate the functional consequences of amino acid changes in EXOSC3 that cause PCH1b, we exploited well-established genetic approaches in Drosophila melanogaster that model EXOSC3 mutations found in individuals with PCH1b. Using this system, we find that the Drosophila EXOSC3 homolog (termed Rrp40) is essential for normal development and has an important function in neurons. Furthermore, PCH1b missense mutations modeled in Rrp40 cause reduced viability and produce neuronal-specific phenotypes that correlate with altered levels of target RNAs that encode factors with key roles in neurons. These results provide a basis for understanding how amino acid changes that occur in the RNA exosome contribute to neuronal dysfunction and disease.

genetics↗