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The thymocyte-specific RNA-binding protein Arpp21 provides TCR repertoire diversity by binding to the 3'-UTR and promoting Rag1 mRNA expression

ABSTRACT: The regulation of thymocyte development by RNA-binding proteins (RBPs) is largely unexplored. We identified 642 RBPs in the thymus and focused on Arpp21, which shows selective and dynamic expression in early thymocytes. Arpp21 was downregulated in response to T cell receptor (TCR) and Ca2+ signals. Downregulation required Stim1/Stim2 and CaMK4 expression and involved Arpp21 protein phosphorylation, polyubiquitination and proteasomal degradation. Arpp21 directly bound RNA through its R3H domain, with a preference for uridine-rich motifs, promoting the expression of target mRNAs. Analysis of the Arpp21-bound transcriptome revealed strong interactions with the Rag1 3'-UTR. Arpp21-deficient thymocytes showed reduced Rag1 expression, delayed TCR rearrangement and a less diverse TCR repertoire. This phenotype was recapitulated in Rag1 3'-UTR mutant mice harboring a deletion of the Arpp21 response region. These findings show how thymocyte-specific Arpp21 promotes Rag1 expression to enable TCR repertoire diversity until signals from the TCR terminate Arpp21 and Rag1 activities.

INSTRUMENT(S): Orbitrap Fusion, Orbitrap Exploris 480

ORGANISM(S): Mus Musculus (ncbitaxon:10090)

SUBMITTER: Henning Urlaub

PROVIDER: MSV000091606 | MassIVE | Fri Mar 31 09:58:00 BST 2023

REPOSITORIES: MassIVE

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The thymocyte-specific RNA-binding protein Arpp21 provides TCR repertoire diversity by binding to the 3'-UTR and promoting Rag1 mRNA expression

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