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Gene expression is tightly regulated by RNA-binding proteins (RBPs) to facilitate cell survival, differentiation, and migration. Previous reports have shown the importance of the Insulin-like Growth Factor II mRNA-Binding Protein (IGF2BP1/IMP1/ZBP1) in regulating RNA fate, including localization, transport, and translation. Here, we generated and characterized a knockout mouse to study RBP regulation. We report that IGF2BP1 is essential for proper brain development and neonatal survival. Specifically, these mice display disorganization in the developing neocortex, and further investigation revealed a loss of cortical marginal cell density at E17.5. We also investigated migratory cell populations in the IGF2BP1[Formula: see text] mice, using BrdU labeling, and detected fewer mitotically active cells in the cortical plate. Since RNA localization is important for cellular migration and directionality, we investigated the regulation of β -actin messenger RNA (mRNA), a well-characterized target with established roles in cell motility and development. To aid in our understanding of RBP and target mRNA regulation, we generated mice with endogenously labeled β -actin mRNA (IGF2BP1[Formula: see text]; β -actin-MS2[Formula: see text]). Using endogenously labeled β -actin transcripts, we report IGF2BP1[Formula: see text] neurons have increased transcription rates and total β -actin protein content. In addition, we found decreased transport and anchoring in knockout neurons. Overall, we present an important model for understanding RBP regulation of target mRNA.

Fragile X syndrome (FXS) is a leading cause of inherited intellectual disability and autism. Whereas dysregulated RNA translation in Fmr1 knockout (KO) mice, a model of FXS, is well studied, little is known about aberrant transcription. Using single-molecule mRNA detection, we show that mRNA encoding the AMPAR subunit GluA2 (but not GluA1) is elevated in dendrites and at transcription sites of hippocampal neurons of Fmr1 KO mice, indicating elevated GluA2 transcription. We identify CPEB3, a protein implicated in memory consolidation, as an upstream effector critical to GluA2 mRNA expression in FXS. Increased GluA2 mRNA is translated into an increase in GluA2 subunits, a switch in synaptic AMPAR phenotype from GluA2-lacking, Ca 2+ -permeable to GluA2-containing, Ca 2+ -impermeable, reduced inhibitory synaptic transmission, and loss of NMDAR-independent LTP at glutamatergic synapses onto CA1 inhibitory interneurons. These factors could contribute to an excitatory/inhibitory imbalance-a common theme in FXS and other autism spectrum disorders., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

RNA binding proteins (RBPs) regulate nearly all post-transcriptional processes within cells. To fully understand RBP function, it is essential to identify their in vivo targets. Standard techniques for profiling RBP targets, such as crosslinking immunoprecipitation (CLIP) and its variants, are limited or suboptimal in some situations, e.g. when compatible antibodies are not available and when dealing with small cell populations such as neuronal subtypes and primary stem cells. This review summarizes and compares several genetic approaches recently designed to identify RBP targets in such circumstances. TRIBE (targets of RNA binding proteins identified by editing), RNA tagging, and STAMP (surveying targets by APOBEC-mediated profiling) are new genetic tools useful for the study of post-transcriptional regulation and RBP identification. We describe the underlying RNA base editing technology, recent applications, and therapeutic implications., Competing Interests: Declaration of interests W.X. and M.R. declare that a PCT patent application (PCT patent application no. PCT/US2016/054525) on the TRIBE technique has been filed. The authors declare no other competing interests., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Learning and memory rely on long-lasting, synapse-specific modifications. Although postsynaptic forms of plasticity typically require local protein synthesis, whether and how local protein synthesis contributes to presynaptic changes remain unclear. Here, we examined the mouse hippocampal mossy fiber (MF)-CA3 synapse, which expresses both structural and functional presynaptic plasticity and contains presynaptic fragile X messenger ribonucleoprotein (FMRP), an RNA-binding protein involved in postsynaptic protein-synthesis-dependent plasticity. We report that MF boutons contain ribosomes and synthesize protein locally. The long-term potentiation of MF-CA3 synaptic transmission (MF-LTP) was associated with the translation-dependent enlargement of MF boutons. Remarkably, increasing in vitro or in vivo MF activity enhanced the protein synthesis in MFs. Moreover, the deletion of presynaptic FMRP blocked structural and functional MF-LTP, suggesting that FMRP is a critical regulator of presynaptic MF plasticity. Thus, presynaptic FMRP and protein synthesis dynamically control presynaptic structure and function in the mature mammalian brain. [Display omitted] • Mossy fiber boutons (MFBs) contain ribosomes and synthesize protein locally • Local presynaptic translation is increased by in vitro and in vivo GC activity • MFB structural plasticity relies on de novo protein synthesis • Presynaptic FMRP is required for MF-CA3 structural and functional plasticity Monday, Kharod et al. report that neuronal activity regulates presynaptic FMRP function and the local synthesis of β-actin. In vitro activity and in vivo experience engage the FMRP-dependent spatiotemporal regulation of protein synthesis that is required for presynaptic remodeling and long-term changes in neurotransmitter release. [ABSTRACT FROM AUTHOR]