Investigating Protein Colocalization with FMRP in Fragile X Syndrome Through Fruit Fly Neuronal and Somatic Models

The m6A-mediated epi-transcriptomic dysregulation drives synaptic dysfunction in fragile X syndrome.

It is demonstrated that FMRP deficiency drives the aberrant translational upregulation of core m6A writers, a causal relationship definitively validated using CGG-corrected isogenic control lines and suggest a promising avenue for m6A-targeted therapies.

FMR1 gene therapy restores translationally relevant phenotypes in a mouse model for fragile X syndrome.

Fragile X Syndrome (FXS) is the most common inherited form of intellectual disability. It is caused by a trinucleotide expansion in the 5' UTR of the Fragile X messenger ribonucleoprotein 1 (FMR1) gene leading to loss of expression of Fragile X messenger ribonucleoprotein (FMRP). There is currently no cure for FXS. We developed an FMR1 gene therapy based on an adeno-associated viral vector designed with strong translational potential for future clinical testing. The viral vector was tested in Fmr1 knockout mice using two translationally relevant delivery routes and ages corresponding to in utero, toddler, and adolescent ages in humans. Functional studies showed that the FMR1 gene therapy improved select translational FXS phenotypes spanning three critical domains: sensory hyperexcitability, adaptation to change, and altered brain activity. Expression after intracerebroventricular injection was most prominent in the forebrain, whereas intravenous delivery predominantly led to expression across midbrain and brainstem, suggesting that a dual route may be needed to achieve full brain coverage. Biodistribution analyses further suggested that FMRP expression must be titrated carefully for optimal rescue. In summary, we show that FMR1 gene therapy using delivery routes and vehicles approved for clinical use improves core phenotypes in a mouse model for FXS.

X-linked SYTL4 missense variant disrupts RAB27A-dependent vesicle trafficking and synaptic transmission in autism.

The findings implicate disrupted SYTL4-RAB27A-dependent vesicle trafficking in ASD pathogenesis and identify SYTL4 and RAB27A as previously unrecognized contributors to autism-associated synaptic deficits and behavior.

Ringer Loss in Drosophila Uncovers Mitochondrial Complex I Deficits Characteristic of Human Parkinson’s Disease

FMRP prevents Me31B/DDX6-associated repression of long neurodevelopmental mRNAs

Long, dosage-sensitive mRNAs encoding neurodevelopmental regulators are selectively dependent on fragile X messenger ribonucleoprotein (FMRP) for efficient translation across animal systems, but the mechanism underlying this length-dependent requirement remains unclear. Here, we show that FMRP maintains translation of long target mRNAs by preventing their inappropriate sequestration into a Me31B/DDX6-dependent P-body repression pathway. In Drosophila oocytes, loss of FMRP caused target mRNAs, but not bulk polyadenylated RNA, to accumulate in Me31B-marked P-bodies. Improved individual-nucleotide resolution crosslinking and immunoprecipitation (iiCLIP) revealed that FMRP and Me31B co-occupy many long coding sequences, suggesting that FMRP targets are intrinsically vulnerable to repressive Me31B-associated machinery. A screen targeting ∼120 candidate genes, followed by proteomic analysis, identified an FMRP-associated ribonucleoprotein (RNP) assembly containing the stress granule-linked proteins Rin/G3BP, Lig/UBAP2L, and Capr/Caprin1. These factors supported translation or localization of distinct FMRP target subsets. Finally, inhibition of Me31B-dependent repressive complex assembly restored translation of the majority of FMRP targets in FMRP-deficient oocytes, supporting a model in which translational failure results from excessive repression. Together, these findings reveal a cytoplasmic RNP assembly that safeguards mRNAs by antagonizing promiscuous P-body repression and provide a mechanistic explanation for the selective vulnerability of long neurodevelopmental transcripts to FMRP loss.

Granule microenvironment regulates the dual functions of FMR1

Fragile X Messenger Ribonucleoprotein 1 (FMR1) is an evolutionarily conserved RNA binding protein with important functions in cognition and female reproduction, and its disruption is associated with neurodevelopmental and reproductive disorders including the Fragile X syndrome. FMR1 is best known for its role as a translation repressor. However, several recent studies also suggest a role of FMR1 as a translation enhancer raising fundamental questions about the molecular regulation of these opposing functions. In this study, we identify FMR1 as part of the oskar mRNA-protein complex in the Drosophila oocyte and study the role of FMR1 as a translational enhancer of oskar. We provide the molecular mechanism for the dual functions of FMR1 and show that the two major RNA-binding domains of FMR1, the KH domains and the RGG box, play distinct separable roles in regulating translation. The KH domains enhance translation of mRNAs while the RGG box containing C-terminal domain (CTD) is required to repress translation. We further show that the condensation propensity of FMR1 containing granules regulates the two antagonistic functions, such that phase separation by FMR1-CTD creates the molecular microenvironment necessary for the repressive activity, whereas reduction in phase separation is associated with increased translation. Our findings highlight the importance of biomolecular condensates not just as a means of molecular compartmentalization but as a fundamental regulatory principle that dictates the functional output of modular protein domains.