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Identification of small molecules rescuing fragile X syndrome phenotypes in Drosophila

Abstract

Fragile X syndrome is caused by the functional loss of the fragile X mental retardation 1 (FMR1) gene. Deletion of the FMR1 ortholog in Drosophila melanogaster (Fmr1) recapitulates many phenotypes associated with fragile X syndrome. We have discovered that Fmr1 mutant Drosophila die during development when reared on food containing increased levels of glutamate, which is consistent with the theory that FMR1 loss results in excess glutamate signaling. Using this lethal phenotype, we screened a chemical library of 2,000 compounds and identified nine molecules that rescued the lethality, including three that implicate the GABAergic inhibitory pathway. Indeed, GABA treatment rescued several known Fmr1 mutant phenotypes in flies, including mushroom bodies defects, excess Futsch translation and abnormal male courtship behavior. These data are consistent with GABAergic inhibition of the enhanced excitatory pathway in fragile X syndrome. In addition, our screen reveals that the muscarinic cholinergic receptors may have a role in fragile X syndrome in parallel to the GABAergic pathway. These results point to potential therapeutic approaches for treating fragile X syndrome.

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Figure 1: A chemical genetic screen to identify small molecules that rescue a Fmr1 mutant phenotype.
Figure 2: GABA treatment rescues glutamate-stimulated toxicity and overexpression of Futsch protein associated with Fmr1 mutants.
Figure 3: GABA treatment rescues β-lobe midline crossing in MBs of Fmr1 mutant flies.
Figure 4: GABA treatment rescues naive courtship behavior in Fmr1 males.
Figure 5: GABAergic pathway is independent of mAChR pathway in rescuing Fmr1-mediated lethality.

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Acknowledgements

We thank S. L'Hernault, T. Kroft, H. Liu and C. Yu for assistance. We thank Y. Feng and the members of the Warren and Jin labs for their assistance and critical comments. We thank T.A. Jongens (University of Pennsylvania) for providing the transgenic fly carrying a copy of the Fmr1 transgene. We also thank the National Institute of Child Health and Human Development (NICHD) Developmental Studies Hybridoma Bank at the University of Iowa for antibodies. S.C. is supported by a Fragile X Research Foundation (FRAXA) postdoctoral grant, and S.M.B. is supported by a Frederick Gardner Cottrell Fellowship at Emory University. This work was supported by US National Institutes of Health grants HD020521 and HD24064 to S.T.W. and by the Colonial Oaks Foundation.

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S.C. designed and performed experiments, analyzed data and wrote the manuscript; S.M.B. performed experiments, analyzed data and revised the manuscript; D.C.Z. and P.J. made initial observations; Z.L. and C.H. conducted the chemical analysis; P.J. designed the research and provided fly strains; S.T.W. designed and supervised the research, wrote and revised the manuscript and obtained funding for the research.

Corresponding author

Correspondence to Stephen T Warren.

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Competing interests

S.T.W. declares he is chair of the Scientific Advisory Board of Seaside Therapeutics, Inc. The remaining authors declare that they have no competing financial interests.

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Chang, S., Bray, S., Li, Z. et al. Identification of small molecules rescuing fragile X syndrome phenotypes in Drosophila. Nat Chem Biol 4, 256–263 (2008). https://doi.org/10.1038/nchembio.78

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