818A Poster - 13. Neural development and physiology
Thursday April 07, 2:00 PM - 4:00 PM

Authors:
Kimberly Rose Madhwani ¹; Sara Ríos Méndez ²; Caley Hogan ³; Jennifer L. Dumouchel ⁴; Jenna Lentini ⁵; Dragony Fu ⁵; Kate M. O'Connor-Giles ^6,7

Affiliations:
1) Neuroscience Graduate Training Program, Brown University, Providence, RI; 2) NIH Post-Baccalaureate Research Education Program (PREP), Brown University, Providence RI; 3) Laboratory of Genetics, University of Wisconsin-Madison, Madison, WI; 4) Molecular Pharmacology & Physiology Graduate Training Program, Brown University, Providence, RI; 5) Department of Biology, University of Rochester, Rochester, NY; 6) Department of Neuroscience, Brown University, Providence, RI; 7) Carney Institute for Brain Science, Providence, RI

Keywords:
c. synaptogenesis; k. developmental disorders

Gene regulation at multiple levels is critical for nervous system development and function. A number of mutations leading to global misregulation of gene expression disproportionately affect the nervous system, resulting in both neurodevelopmental and degenerative disorders. Emerging work demonstrates that post-transcriptional modification of transfer RNAs (tRNAs) regulates tRNA stability and codon-anticodon pairing and, thus, translation rate and fidelity. ALKBH8 is one of two metazoan homologs of the yeast tRNA methyltransferase TRM9. Mutations in the highly conserved human ALKBH8 were recently found to cause intellectual disability in three families. However, ALKBH8’s role in the nervous system is unknown. In yeast, TRM9 methylates uridines in the wobble position of the anticodon loop to reinforce cognate codon-anticodon pairings, resulting in increased translation of mRNAs enriched for cognate codons. We generated ALKBH8 null mutants and analyzed tRNA post-transcriptional modifications in the brain by mass spectrometry. We observed a complete loss of wobble uridine methylation in Drosophila ALKBH8 null mutants, consistent with prior findings in mammals. We next investigated a role for ALKBH8 in nervous system development and found that ALKBH8 attenuates synaptic growth. In addition, we found that ALKBH8 mutants exhibit increased levels of and sensitivity to reactive oxygen species (ROS). ALKBH8 is required to methylate tRNA-selenocysteine, which enables the incorporation of selenocysteine into selenoproteins. Selenoproteins are potent regulators of oxidative stress, and we have found that blocking selenoprotein synthesis by other means also results in synaptic overgrowth. Interestingly, oxidative stress has been shown to manifest in synaptic overgrowth. To determine if increased ROS and synaptic overgrowth in ALKBH8 mutants are causally linked, we treated ALKBH8 null animals with the antioxidant N-acetylcysteine amide and found that synaptic growth is partially rescued. These findings support a model in which ALKBH8 regulates synaptic growth through its role in regulating ROS via methylation of tRNA-selenocysteine, and reveals antioxidants as a potential therapeutic treatment for individuals with ALKBH8-linked intellectual disability.