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Mutations in distinct translation-dependent quality control pathways lead to convergent molecular pathogenesis and neurodevelopmental defects.

ABSTRACT: Translation-dependent quality control pathways govern protein synthesis and proteostasis by degrading potentially toxic peptide products derived from aberrant mRNAs. However, little is known about the in vivo defects that arise in the absence of these pathways and how translation is altered in the absence of these pathways. Here, we demonstrate that the ribosome rescue factors Pelo/Hbs1l are both critical for embryonic and neuronal development but dispensable for neuronal survival in the adult brain. Loss of Pelo/Hbs1l in cerebellar progenitors impaired differentiation of these cells. Our analysis of Pelo/Hbs1l deficient fibroblasts revealed translational reprogramming of multiple pathways including mTORC1 signaling likely to restore cellular homeostasis. Interestingly, similar affects on the translatome, signaling pathways and neurogenesis were observed when we conditionally deleted Upf2 to inhibit NMD. These data reveal that translation-dependent quality control pathways, which set out to mitigate errors in translation and to clear defective peptide products and aberrant mRNAs can trigger similar cellular responses and neurodevelopmental abnormalities.

ORGANISM(S): Mus musculus

PROVIDER: GSE162556 | GEO | 2021/03/15

REPOSITORIES: GEO

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Project description:Hbs1 has been established as a central component of the cell’s translational quality control pathways in both yeast and prokaryotic models; however, the functional characteristics of its human ortholog (Hbs1L) have not been well-defined. We recently reported a novel human phenotype resulting from a mutation in the critical coding region of the HBS1L gene characterized by facial dysmorphism, severe growth restriction, axial hypotonia, global developmental delay and retinal pigmentary deposits. Here we further characterize downstream effects of the human HBS1L mutation. HBS1L has three transcripts in humans, and RT-PCR demonstrated reduced mRNA levels corresponding with transcripts V1 and V2 whereas V3 expression was unchanged. Western blot analyses revealed HBS1L protein was absent in proband samples. Additionally, polysome profiling revealed an abnormal aggregation of 80S monosomes in patient cells under baseline conditions. RNASeq data corresponded to the patient phenotype, with biological process analysis showing skeletal system development and sensory development genes being most altered between patient and controls. Ribosomal sequencing demonstrated an increased translation efficiency of ribosomal RNA in Hbs1L-deficient fibroblasts, suggesting that there may be a compensatory increase in ribosome translation to accommodate the increased 80S monosome peak. Furthermore, lack of Hbs1L caused depletion of Pelota protein in both patient cells and mouse tissues, while PELO mRNA levels were unaffected. Inhibition of proteasomal function partially restored Pelota expression in human Hbs1L-deficient cells. We also describe a mouse model harboring a knockdown mutation in the murine Hbs1l gene that shared several of the phenotypic elements observed in the Hbs1L-deficient human including facial dysmorphism, growth restriction and retinal deposits. The Hbs1lKO mice similarly demonstrate diminished Pelota levels that were rescued by proteasome inhibition.

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Mutations in distinct translation-dependent quality control pathways lead to convergent molecular pathogenesis and neurodevelopmental defects.

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