The Multifaceted Roles of Fragile X Mental Retardation Protein in Developmental Plasticity at a Central Synapse
Bibliographic record
Abstract
During their critical period of sensory development, postsynaptic glutamatergic receptors, namely AMPA receptors (AMPARs) and NMDA receptors (NMDARs), undergo rapid remodeling in abundance and composition to enable fast neurotransmission. Dysregulation of this process can lead to neurodevelopmental disorders such as Fragile X Syndrome (FXS) which shares several mental retardation-associated features of Autism Spectrum Disorders (ASD). This is caused by a loss of Fragile X Mental Retardation Protein (FMRP), a critical translational repressor at the synapse recently implicated in ion channel modulation. To investigate the roles of FMRP in synaptic remodeling of glutamatergic receptors, I have established developmental profiles at the calyx of Held-MNTB synapse in the auditory brainstem by measuring whole-cell electrophysiological synaptic responses from pre-ear canal opening (post-natal day 6-9) and after-hearing onset (post-natal day 16-19) synapses in wild-type and the FMR1-/- mouse model of human FXS. My results indicate the loss of FMRP causes early maturation of AMPARs by accelerating the developmental switch from the slower-gating GluA1-dominant to faster-gating GluA4-dominant subunit composition of AMPARs, consistent with the canonical role of FMRP as an mRNA translational repressor. In contrast, developmental downregulation of NMDARs is not only stunted in FMR1-/- synapses, but also resistant to activity-dependent downregulation. This defect can be acutely rescued by intracellular delivery of the protein binding N-terminus fragment of FMRP during whole-cell patch clamp recordings, suggesting FMRPN-terminal is sufficient for mediating activity-dependent plasticity of NMDARs. Importantly, pulldown of the NMDAR subunit GluN1 and mGluR5 by FMRP in co-immunoprecipitation experiments provides evidence of FMRP binding to mGluR5-NMDAR complexes. This raises the possibility that a protein-protein interaction involving FMRP is engaged in the developmental downregulation of NMDARs. Based on these novel findings, I propose a model whereby activity induced increases in intracellular calcium triggers a two-pronged biochemical cascade through which FMRP differentially regulates two glutamatergic receptors within the same cell type. Altogether, FMRP functions as a canonical translational repressor to regulate AMPAR subunit expression, as well as as a non-canonical signaling molecule to mediate activity-dependent downregulation of NMDARs. These deficits in developmental synaptic remodeling provide mechanistic insights into the sensory hypersensitivity and cognitive impairments in FXS and ASD.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".