UMMS Affiliation

Program in Molecular Medicine

Publication Date


Document Type



Amino Acids, Peptides, and Proteins | Biochemistry, Biophysics, and Structural Biology | Congenital, Hereditary, and Neonatal Diseases and Abnormalities | Neuroscience and Neurobiology | Nucleic Acids, Nucleotides, and Nucleosides


RNA-binding proteins (RBPs) function in higher-order assemblages such as RNA granules to regulate RNA localization and translation. The Fragile X homolog FXR2P is an RBP essential for formation of neuronal Fragile X granules that associate with axonal mRNA and ribosomes in the intact brain. However, the FXR2P domains important for assemblage formation in a cellular system are unknown. Here we used an EGFP insertional mutagenesis approach to probe for FXR2P intrinsic features that influence its structural states. We tested 18 different in-frame FXR2P(EGFP) fusions in neurons and found that the majority did not impact assemblage formation. However, EGFP insertion within a 23 amino acid region of the low complexity (LC) domain induced FXR2P(EGFP) assembly into two distinct fibril states that were observed in isolation or in highly-ordered bundles. FXR2P(EGFP) fibrils exhibited different developmental timelines, ultrastructures and ribosome associations. Formation of both fibril types was dependent on an intact RNA-binding domain. These results suggest that restricted regions of the LC domain, together with the RNA-binding domain, may be important for FXR2P structural state organization in neurons.


Fragile X syndrome, Local protein synthesis, Low complexity, RNA granule, RNA-binding protein

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© 2019. Published by The Company of Biologists Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed.

DOI of Published Version



Biol Open. 2019 Aug 21;8(8). pii: 8/8/bio046383. doi: 10.1242/bio.046383. Link to article on publisher's site

Journal/Book/Conference Title

Biology open

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Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.