Talks by Adham SAFIEDDINE and Benoit PALANCADE

Adham SAFIEDDINE
Institut de biologie Paris-Seine IBPS, CNRS

Title:
Cell cycle-dependent mRNA localization in P-bodies

Abstract:
Understanding the dynamics of RNA targeting to membraneless organelles is essential to disentangle their functions. Notably, whether p-bodies (PBs) participate in regulation of gene expression remains unclear. To tackle this question, we investigate how PBs evolve during cell cycle progression. PB purification across the cell cycle uncovers widespread changes in their RNA content, which are partly uncoupled from cell cycle-dependent changes in RNA expression. Single molecule FISH shows various mRNA localization patterns in PBs peaking in G1, S, or G2, with examples illustrating the timely capture of mRNAs in PBs when their encoded protein becomes dispensable. However, rather than directly reflecting absence of translation, cyclic mRNA localization in PBs is controlled by extrinsic (RNA binding proteins) and intrinsic (RNA features) factors. Indeed, while PB mRNAs are AU-rich at all cell cycle phases, they are specifically longer in G1, suggesting their involvement in post-mitotic PB reassembly. Altogether, our study supports a model where PBs are more than a default location for excess untranslated mRNAs.

Benoit PALANCADE
RNA biogenesis and genome homeostasis, Institut Jacques Monod, CNRS, Université Paris Cité, Paris, France

Title: Nuclear pore complex assembly: a matter of mRNA translation

Abstract:
Our lab is generally interested in the mechanisms that keep in check the assembly and the localization of mRNA particles in eukaryotic cells, thereby influencing gene expression and genome stability. In this frame, we have notably explored the collective regulations that target functionally-related mRNAs, i.e. those encoding the subunits of multiprotein complexes. By focusing on the nuclear pore complex (NPC), a sophisticated proteinaceous machine encompassing hundreds of subunits (a.k.a. nucleoporins or Nups), we have identified post-transcriptional regulations that synchronize the production of individual polypeptides with their assembly and delivery to the nuclear envelope. Using systematic RNA immunoprecipitation, RNP proteomics and RNA imaging in yeast, we found that translational repression of Nup-encoding mRNAs restricts the production of NPC subunits, a mechanism that can be alleviated upon increase of the cellular demand for NPCs. In addition, we observed that several Nups establish binary interactions with their protein partners in a co-translational manner, in the cytoplasm. Strikingly, a subset of Nup-encoding mRNAs is targeted and locally translated at the nuclear envelope, coupling the synthesis of nucleoporins with their final delivery to assembling NPCs. The cis-and trans-acting factors that specifically regulate Nup mRNA metabolism and thus impact NPC homeostasis will be discussed.