BMC Seminar Monday, 13th of June at 10:00 in room 343.

Speaker: Miha Modic, Institute of Stem Cell Research, Helmholtz Center Munich, Neuherberg, Germany & MRC Laboratory of Molecular Biology Cambridge, Cambridge, United Kingdom.

Title: RNA BINDING PROTEIN TDP-43 SAFEGUARDS PLURIPOTENCY BY REGULATION OF DEVELOPMENTAL ALTERNATIVE POLYADENYLATION PREVENTING PARASPECKLE ASSEMBLY

Abstract: How pluripotent stem cells (PSCs) exit the self-renewing program and become committed to embryonic lineages is a fundamental question.Transcriptional, signaling and epigenetic regulation of PSC fate decisions have been the focus of research, while the understanding of RNA based mechanisms in rapid dissolvent of the self-renewing reprogramming apparatus in PSCs has been lagging behind. Recently, several studies have identified RNA-binding proteins (RBPs) as modifiers of pluripotency.Additionally, pluripotency specific pattern of alternative polyadenylation(APA) is dynamically regulated during early PSC differentiation and reprogramming. However, the factors regulating APA are still poorly understood and it is unknown what mechanisms are employed by the relevant RBPs on a transcriptomic level to regulate pluripotency breakdown.We elucidated a novel TDP-43 function in global developmental regulation of APA including core pluripotency circuitry, role of APA in paraspeckle formation and the role of TDP-43 mediated APA regulation in differentiation of mouse and human PSCs.We show that unique subnuclear structures termed paraspeckles are formed independent of lineage type during exit from the pluripotency and are important for stabilization of the early commitment state. The long isoform of non-coding RNA NEAT1 serves as the scaffold for paraspeckles assembly produced only upon differentiation. We present evidence that TDP-43maintains production of nucleoplasmic NEAT1 short isoform by directly regulating APA of nascent NEAT1 transcripts in undifferentiated cells, and that TDP-43 itself is sequestered in paraspeckles upon differentiation leading to formation of NEAT1 long isoform and paraspeckle assembly. This indicates the existence of a feed-forward feedback mechanism underlying paraspeckle assembly during onset of differentiation. Furthermore, we analyzed how paraspeckle assembly regulates exit from pluripotency; we show that cells lacking NEAT1 and paraspeckle proteins exhibit severe developmental delay. Together, this work implicates developmental regulation of APA in RNA-mediated nuclear restructuring leading to stabilization of the early differentiation state and pluripotency breakdown.