title: Full UPF3B function is critical for neuronal differentiation of neural stem cells.
abstract: BACKGROUND
  Mutation in the UPF3B gene on chromosome X is implicated in neurodevelopmental disorders including X-linked intellectual disability, autism and schizophrenia. The protein UPF3B is involved in the nonsense-mediated mRNA decay pathway (NMD) that controls mRNA stability and functions in the prevention of the synthesis of truncated proteins.
  
  
  RESULTS
  Here we show that NMD pathway components UPF3B and UPF1 are down-regulated during differentiation of neural stem cells into neurons. Using tethered function assays we found that UPF3B missense mutations described in families with neurodevelopmental disorders reduced the activity of UPF3B protein in NMD. In neural stem cells, UPF3B protein was detected in the cytoplasm and in the nucleus. Similarly in neurons, UPF3B protein was detected in neurites, the somatic cytoplasm and in the nucleus. In both cell types nuclear UPF3B protein was enriched in the nucleolus. Using GFP tagged UPF3B proteins we found that the missense mutations did not affect the cellular localisation. Expression of missense mutant UPF3B disturbed neuronal differentiation and reduced the complexity of the branching of neurites. Neuronal differentiation was similarly affected in the presence of the NMD inhibitor Amlexanox. The expression of mutant UPF3B proteins lead to a subtle increase in mRNA levels of selected NMD targets.
  
  
  CONCLUSIONS
  Together our findings indicate that, despite the down-regulation of NMD factors, functional NMD is critical for neuronal differentiation. We propose that the neurodevelopmental phenotype of UPF3B missense mutation is caused by impairment of NMD function altering neuronal differentiation.
authors.affiliation: University of Aberdeen, Institute of Medical Sciences, Foresterhill, Aberdeen AB25 2ZD, Scotland, UK. ph.tahani@riyadh.edu.sa.|Current address: Riyadh Colleges of Dentistry and Pharmacy, Olaya Campus, Riyadh, Saudi Arabia. ph.tahani@riyadh.edu.sa.
authors.forename: Tahani
authors.initials: T
authors.lastname: Alrahbeni
authors.affiliation: University of Aberdeen, Institute of Medical Sciences, Foresterhill, Aberdeen AB25 2ZD, Scotland, UK. r04fs12@abdn.ac.uk.
authors.forename: Francesca
authors.initials: F
authors.lastname: Sartor
authors.affiliation: University of Aberdeen, Institute of Medical Sciences, Foresterhill, Aberdeen AB25 2ZD, Scotland, UK. r01ja13@abdn.ac.uk.
authors.forename: Jihan
authors.initials: J
authors.lastname: Anderson
authors.affiliation: Medical Genetics, Polwarth Building, Foresterhill, Aberdeen AB25 2ZD, Scotland, UK. zosia@abdn.ac.uk.
authors.forename: Zosia
authors.initials: Z
authors.lastname: Miedzybrodzka
authors.affiliation: University of Aberdeen, Institute of Medical Sciences, Foresterhill, Aberdeen AB25 2ZD, Scotland, UK. c.mccaig@abdn.ac.uk.
authors.forename: Colin
authors.initials: C
authors.lastname: McCaig
authors.affiliation: University of Aberdeen, Institute of Medical Sciences, Foresterhill, Aberdeen AB25 2ZD, Scotland, UK. b.mueller@abdn.ac.uk.
authors.forename: Berndt
authors.initials: B
authors.lastname: Müller
mesh_terms: D002454:Cell Differentiation; D004260:DNA Repair; D015536:Down-Regulation; D006367:HeLa Cells; D006801:Humans; D020125:Mutation, Missense / Q000235:genetics; D058953:Neural Stem Cells / Q000166:cytology* / Q000378:metabolism; D016501:Neurites / Q000378:metabolism; D009474:Neurons / Q000166:cytology* / Q000378:metabolism; D059365:Nonsense Mediated mRNA Decay; D021381:Protein Transport; D020365:RNA Helicases; D016601:RNA-Binding Proteins / Q000378:metabolism*; D015534:Trans-Activators / Q000378:metabolism
chemical_list: D016601:RNA-Binding Proteins; D015534:Trans-Activators; C435488:UPF3B protein, human; D020365:RNA Helicases; C101828:UPF1 protein, human