New findings in RNA modification: A PUSsible cause of intellectual disorders

How much do we know about the causes of intellectual disability and neurodevelopment disorders? Recent advances in genetics studies have led to discover more than 1000 genes that are inked to neuronal diseases formation. Unfortunately, the details of underlying mechanisms are still missing.

Recently, a subpopulation of patients who show wide spectrums of abnormality in developments are found to carry various mutations in the same gene called pseudouridine synthase 3 (pus3). This gene encodes PUS3 protein that is responsible for converting uridine to pseudouridine. PUS3 works on the specific position 39 on some tRNAs. Overall structure of pseudouridine looks like uridine but pseudouridine has an additional bond that allows it to increase RNA structure stability. The stabilized tRNA can then fulfill its role in protein translation.

We and collaborators recently identified three independent Polish patients who carry mutations in pus3 gene. In order to understand the pathological link of the mutations to disease formation, we implemented two strategies i) biochemical characterizations of PUS3 protein; ii) examine PUS3 protein-related effects in cells.

Firstly, we managed to produce the first available recombinant human PUS3 protein. It became feasible for us to characterize the protein features. We provide the evidence that one homozygotic variant displays relatively low stability while one heterozygotic variant shows a highly aggregated profile. In parallel, we established cell lines that are derived from patients’ cells and measured PUS3 protein expression. Surprisingly, we observed almost lost of PUS3 protein in cells. This is in agreement with the observation in the in vitro tests. In addition, we could not detect PUS3-dependent pseudouridine products in tRNAs. This defect could disturb the overall protein productions in cells.

Altogether, our study provides the explanation on how some PUS3 mutations cause neurodevelopment disorders. Other mutations in PUS3 might disable the protein activity in different ways, we now have the chance to examine them in the future and provide further insights in the details in their pathological relations to diseases.

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