Publications by authors named "Joana V Flores"

4 Publications

  • Page 1 of 1

Cytosine-5 RNA Methylation Regulates Neural Stem Cell Differentiation and Motility.

Stem Cell Reports 2017 01 29;8(1):112-124. Epub 2016 Dec 29.

Wellcome Trust - Medical Research Council Cambridge Stem Cell Institute, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK; Department of Genetics, University of Cambridge, Downing Street, Cambridge CB2 3EH, UK. Electronic address:

Loss-of-function mutations in the cytosine-5 RNA methylase NSUN2 cause neurodevelopmental disorders in humans, yet the underlying cellular processes leading to the symptoms that include microcephaly remain unclear. Here, we show that NSUN2 is expressed in early neuroepithelial progenitors of the developing human brain, and its expression is gradually reduced during differentiation of human neuroepithelial stem (NES) cells in vitro. In the developing Nsun2 mouse cerebral cortex, intermediate progenitors accumulate and upper-layer neurons decrease. Loss of NSUN2-mediated methylation of tRNA increases their endonucleolytic cleavage by angiogenin, and 5' tRNA fragments accumulate in Nsun2 brains. Neural differentiation of NES cells is impaired by both NSUN2 depletion and the presence of angiogenin. Since repression of NSUN2 also inhibited neural cell migration toward the chemoattractant fibroblast growth factor 2, we conclude that the impaired differentiation capacity in the absence of NSUN2 may be driven by the inability to efficiently respond to growth factors.
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http://dx.doi.org/10.1016/j.stemcr.2016.11.014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5233436PMC
January 2017

Aberrant methylation of tRNAs links cellular stress to neuro-developmental disorders.

EMBO J 2014 Sep 25;33(18):2020-39. Epub 2014 Jul 25.

Wellcome Trust - Medical Research Council Cambridge Stem Cell Institute, University of Cambridge, Cambridge, UK

Mutations in the cytosine-5 RNA methyltransferase NSun2 cause microcephaly and other neurological abnormalities in mice and human. How post-transcriptional methylation contributes to the human disease is currently unknown. By comparing gene expression data with global cytosine-5 RNA methylomes in patient fibroblasts and NSun2-deficient mice, we find that loss of cytosine-5 RNA methylation increases the angiogenin-mediated endonucleolytic cleavage of transfer RNAs (tRNA) leading to an accumulation of 5' tRNA-derived small RNA fragments. Accumulation of 5' tRNA fragments in the absence of NSun2 reduces protein translation rates and activates stress pathways leading to reduced cell size and increased apoptosis of cortical, hippocampal and striatal neurons. Mechanistically, we demonstrate that angiogenin binds with higher affinity to tRNAs lacking site-specific NSun2-mediated methylation and that the presence of 5' tRNA fragments is sufficient and required to trigger cellular stress responses. Furthermore, the enhanced sensitivity of NSun2-deficient brains to oxidative stress can be rescued through inhibition of angiogenin during embryogenesis. In conclusion, failure in NSun2-mediated tRNA methylation contributes to human diseases via stress-induced RNA cleavage.
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http://dx.doi.org/10.15252/embj.201489282DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4195770PMC
September 2014

The mouse cytosine-5 RNA methyltransferase NSun2 is a component of the chromatoid body and required for testis differentiation.

Mol Cell Biol 2013 Apr 11;33(8):1561-70. Epub 2013 Feb 11.

Wellcome Trust-Medical Research Council Stem Cell Institute, University of Cambridge, Cambridge, United Kingdom.

Posttranscriptional regulatory mechanisms are crucial for protein synthesis during spermatogenesis and are often organized by the chromatoid body. Here, we identify the RNA methyltransferase NSun2 as a novel component of the chromatoid body and, further, show that NSun2 is essential for germ cell differentiation in the mouse testis. In NSun2-depleted testes, genes encoding Ddx4, Miwi, and Tudor domain-containing (Tdr) proteins are repressed, indicating that RNA-processing and posttranscriptional pathways are impaired. Loss of NSun2 specifically blocked meiotic progression of germ cells into the pachytene stage, as spermatogonial and Sertoli cells were unaffected in knockout mice. We observed the same phenotype when we simultaneously deleted NSun2 and Dnmt2, the only other cytosine-5 RNA methyltransferase characterized to date, indicating that Dnmt2 was not functionally redundant with NSun2 in spermatogonial stem cells or Sertoli cells. Specific NSun2- and Dnmt2-methylated tRNAs decreased in abundance when both methyltransferases were deleted, suggesting that RNA methylation pathways play an essential role in male germ cell differentiation.
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http://dx.doi.org/10.1128/MCB.01523-12DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3624257PMC
April 2013

Mutation in NSUN2, which encodes an RNA methyltransferase, causes autosomal-recessive intellectual disability.

Am J Hum Genet 2012 May 26;90(5):856-63. Epub 2012 Apr 26.

Molecular Neuropsychiatry & Development Lab, Neurogenetics Section, Centre for Addiction and Mental Health, Toronto, Canada.

Causes of autosomal-recessive intellectual disability (ID) have, until very recently, been under researched because of the high degree of genetic heterogeneity. However, now that genome-wide approaches can be applied to single multiplex consanguineous families, the identification of genes harboring disease-causing mutations by autozygosity mapping is expanding rapidly. Here, we have mapped a disease locus in a consanguineous Pakistani family affected by ID and distal myopathy. We genotyped family members on genome-wide SNP microarrays and used the data to determine a single 2.5 Mb homozygosity-by-descent (HBD) locus in region 5p15.32-p15.31; we identified the missense change c.2035G>A (p.Gly679Arg) at a conserved residue within NSUN2. This gene encodes a methyltransferase that catalyzes formation of 5-methylcytosine at C34 of tRNA-leu(CAA) and plays a role in spindle assembly during mitosis as well as chromosome segregation. In mouse brains, we show that NSUN2 localizes to the nucleolus of Purkinje cells in the cerebellum. The effects of the mutation were confirmed by the transfection of wild-type and mutant constructs into cells and subsequent immunohistochemistry. We show that mutation to arginine at this residue causes NSUN2 to fail to localize within the nucleolus. The ID combined with a unique profile of comorbid features presented here makes this an important genetic discovery, and the involvement of NSUN2 highlights the role of RNA methyltransferase in human neurocognitive development.
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http://dx.doi.org/10.1016/j.ajhg.2012.03.023DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3376419PMC
May 2012