Kharod, S. C. | Search bioRxiv

bioRxiv2023

Regulation of FMRP granule structure and function through phosphorylation

Fragile X messenger ribonucleoprotein (FMRP) is an RNA-binding protein implicated in autism that suppresses translation and forms granules. While FMRP function has been well-studied, how phosphorylation regulates granule binding and function remains limited. Here, we found that Fragile X patient-derived I304N mutant FMRP could not stably bind granules, underscoring the essential nature of FMRP granule association for function. Next, phosphorylation on serine 499 (S499) led to differences in puncta size, intensity, contrast, and transport as shown by phospho-deficient (S499A) and phospho-mimic (S499D) mutant FMRP granules. Additionally, S499D exchanged slowly on granules relative to S499A, suggesting that phosphorylated FMRP can attenuate translation. Furthermore, the S499A mutant enhanced translation in presynaptic boutons of the mouse hippocampus. Thus, the phospho-state of FMRP altered the structure of individual granules with changes in transport and translation to achieve spatiotemporal regulation of local protein synthesis. TeaserThe phosphorylation-state of S499 on FMRP can change FMRP granule structure and function to facilitate processive transport or local protein synthesis.

neuroscience↗

bioRxiv2021

Presynaptic FMRP and local protein synthesis support structural and functional plasticity of glutamatergic axon terminals

Learning and memory critically rely on long-lasting, synapse-specific modifications. While postsynaptic forms of plasticity typically require local protein synthesis, whether and how local protein synthesis contributes to presynaptic changes remains unclear. Here, we examined the hippocampal mossy fiber (MF)-CA3 synapse which expresses both structural and functional presynaptic plasticity. We report that MF boutons synthesize protein locally and contain ribosomes. Long-term potentiation of MF-CA3 synaptic transmission (MF-LTP) was associated with translation-dependent enlargement of MF boutons. Moreover, increasing in vitro and in vivo MF activity enhanced protein synthesis in MFs. Remarkably, deletion of presynaptic Fragile X mental retardation protein (FMRP), an RNA-binding protein expressed in MF boutons and previously implicated in local postsynaptic protein synthesis-dependent plasticity, blocked structural and functional MF-LTP, suggesting that FMRP is a critical regulator of presynaptic function. Thus, presynaptic FMRP and protein synthesis dynamically control presynaptic structure and function in the mature brain. HighlightsO_LIMossy fiber boutons (MFBs) synthesize protein locally and contain ribosomes C_LIO_LILocal presynaptic translation is increased by in vitro and in vivo GC activity C_LIO_LIMFB structural plasticity relies on de novo protein synthesis. C_LIO_LIPresynaptic FMRP is required for MF-CA3 structural and functional plasticity C_LI In BriefMonday et al. report that FMRP and protein synthesis in hippocampal mossy fiber boutons mediate functional and structural presynaptic plasticity.

neuroscience↗