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Loss of Larp1 disrupts the synaptic localization of TOP mRNAs and impairs spatial memory.

ABSTRACT: Post-transcriptional regulation of mRNAs allows for rapid and local control of gene expression. In vertebrates, the mTOR Complex 1 pathway post-transcriptionally controls the translation and stability of terminal oligopyrimidine motif mRNAs (TOP mRNAs), which encode ribosomal proteins and other essential factors. These mRNAs also preferentially localize to neuronal synapses, axons and dendrites, suggesting a role in growth and/or plasticity. To determine brain functions of TOP regulation, we generated mice where La-related protein 1 (Larp1), the TOP regulator downstream of mTORC1, is inactivated in neurons. These mice are viable but brain size is significantly reduced. The translation of TOP mRNAs is derepressed, but mRNA levels are depleted more than 50%. Depletion was exacerbated at synapses, reversing the enrichment observed in wild-type neurons, and accompanied by impaired spatial memory. These observations highlight the importance of post-transcriptional regulation of TOP mRNAs for brain growth and neuronal functions underlying learning and memory.

ORGANISM(S): Mus musculus

PROVIDER: GSE286175 | GEO | 2026/02/18

REPOSITORIES: GEO

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GCN2 suppresses TOP mRNA translation via LARP1

Project description:La-related protein 1 (LARP1) has been identified as a key translational inhibitor of terminal oligopyrimidine tract (TOP) mRNAs downstream of the nutrient sensing protein kinase complex, mTORC1. LARP1 exerts this inhibitory effect on TOP mRNA translation by binding to the mRNA cap and the adjacent 5’TOP motif, resulting in the displacement of the eIF4E complex from TOP mRNAs. In the present study, we identify a second nutrient sensing kinase GCN2 that converges on LARP1 to control TOP mRNA translation. GCN2 inhibits TOP mRNA translation via ATF4-dependent transcriptional induction of LARP1 mRNAs and GCN1-mediated recruitment of LARP1 to stalled ribosomes. We performed ATF4 ChIP-seq experiments in both WT and GCN2 KO MEFs with or without leucine deprivation.

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mTOR- and LARP1-dependent regulation of TOP mRNA poly(A) tail and ribosome loading [LARP1 KD, Torin1]

Project description:Translation of TOP mRNAs encoding protein synthesis machinery is strictly regulated by an amino acid sensing mTOR pathway. However, its regulatory mechanism remains elusive. Here, we demonstrate that TOP mRNA translation positively correlates with its poly(A) tail length under mTOR active/amino acid-rich condition, suggesting that TOP mRNAs are post-transcriptionally controlled by poly(A) tail length regulation. Consistent with this, tail length of TOP mRNAs dynamically fluctuates in response to amino acid availability. Poly(A) tail shortens under mTOR active/ amino acid-rich condition, whereas the long-tailed TOP mRNAs accumulate under mTOR inactive/amino acid-starved (AAS) condition. An RNA-binding protein LARP1 that specifically binds to TOP mRNAs is indispensable for the process. We also show that LARP1 interacts with non-canonical poly(A) polymerases, PAPD4, PAPD5 and PAPD7 and induces post-transcriptional polyadenylation of the target when tethered to the mRNA. Our findings illustrate that LARP1 contributes to the selective accumulation of TOP mRNAs with long poly(A) tail under AAS, resulting in accelerated ribosomal loading onto TOP mRNAs for the resumption of translation after AAS.

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LARP1 senses free ribosomes to coordinate supply and demand of ribosomal proteins

Project description:Terminal oligopyrimidine motif-containing (TOP) mRNAs encode all ribosomal proteins in mammals and are regulated to tune ribosome synthesis to cell state. Previous studies implicate LARP1 in 40S- or 80S-ribosome complexes that repress and stabilize TOP mRNAs. However, a mechanistic understanding of how LARP1 and TOP mRNAs interact with ribosomes to coordinate TOP mRNA outcomes is lacking. Here, we show that LARP1 senses the cellular supply of ribosomes by directly binding non-translating 80S ribosomes. Cryo-EM structures reveal a previously uncharacterized domain of LARP1 bound to and occluding the 40S mRNA channel and mutations at the LARP1-ribosome interface block formation of the 40S/80S-LARP1-TOP complexes. Free cytosolic ribosomes induce sequestration of TOP mRNAs in repressed 80S-LARP1-TOP complexes independent of alterations in mTOR signaling. Together, this work demonstrates a ribosome-sensing function of LARP1 that allows it to tune ribosome protein synthesis to the availability of free ribosomes.

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eIF4A1 enhances LARP1-mediated translational repression during mTORC1 inhibition

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mTORC1 controls a dynamic program of TOP mRNA translation via LARP1

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Post-transcriptional regulation of Ribosome Biogenesis in Larp1-deficient cells

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Project description:The RNA biding protein, LARP1, has been proposed to function downstream of mTORC1 to positively regulate the translation of 5’TOP mRNAs such as ribosome protein (RP) mRNAs. However, its regulatory roles in mTORC1-mediated translation remain unclear. PAR-CLIP of LARP1 revealed its direct and dynamic interactions with RP mRNAs through pyrimidine-enriched sequences in the 5’UTR of RP mRNAs when mTOR activity is inhibited. Importantly, this LARP1 is a direct substrate of mTORC1 and S6K1/Akt, and phosphorylated LARP1 scaffolds mTORC1 on translation-competent mRNAs to facilitate 4EBP1 and S6K1 phosphorylation. Ablation of LARP1 causes multiple defects in the processes of translation including abnormal eIF4G1 interaction with RP mRNAs and inefficient RP mRNA elongation thereby reducing ribosome biogenesis and cell proliferation. These observations illustrate that LARP1 functions both an effector and a regulator for local mTORC1 activity, and acts as a molecular switch for ribosome biogenesis by sensing growth factor/nutrient signaling.

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