Project description:The identification of RNAs that are recognized by RNA-binding proteins (RNA-BPs) using techniques such as Crosslinking and Immunoprecipitation (CLIP) has revolutionized the genome-wide discovery of RNA-BP RNA targets. Among the different versions of CLIP that have been developed, the use of photoactivable nucleoside analogs has resulted in high efficiency photoactivable ribonucleoside-enhanced CLIP (PAR-CLIP) in vivo. Nonetheless, PAR-CLIP has not yet been applied in prokaryotes. To determine if PAR-CLIP can be used in prokaryotes, we determined suitable conditions for the incorporation of 4-thiouridine (4SU), a photoactivable nucleoside, into E. coli RNA and for the isolation of RNA crosslinked to RNA-BPs of interest. Applying this technique to Hfq, a well-characterized regulator of small RNA (sRNA)-messenger RNA (mRNA) interactions, we showed that PAR-CLIP identified most of the known sRNA targets of Hfq, as well as functionally relevant sites of Hfq-mRNA interactions at nucleotide resolution. Based on our findings, PAR-CLIP represents an improved method to identify both the RNAs and the specific regulatory sites that are recognized by RNA-BPs in prokaryotes.
Project description:We show that Treacle promotes phase separation of TOPBP1 within the FC to initiate spatially confined n-DDR signaling and to direct rDNA repair pathway choice. Using both a reductionist FKBP-based system for inducible TOPBP1 oligomerization and physiological models of genotoxic rDNA damage, we demonstrate that phosphorylation of Treacle at Ser1191 by CK2 and at Ser1199 by ATR/ATM enables bivalent engagement of the BRCT2 and BRCT5 domains of TOPBP1, thereby nucleating Treacle-dependent TOPBP1 condensation. This condensate is further stabilized by TOPBP1 oligomerization via its BRCT7/8 domains, giving rise to a nested, “Russian doll”-like phase architecture that spatially and temporally compartmentalizes DDR signaling within the nucleolus. Functionally, Treacle-dependent TOPBP1 condensation initiates γH2AX signaling and promotes recruitment of DNA repair factors in a stress-dependent manner. Importantly, disruption of this condensation does not abolish rDNA double-strand break repair but biases repair toward rapid DNA-PK–dependent non-homologous end joining, while impairing ATR/ATM activation and late-phase homologous recombination–associated repair. Consistent with this, Treacle-knockout cells exhibit accelerated early rDNA repair kinetics but incomplete damage resolution at later stages. Together, our findings identify Treacle as a molecular platform that coordinates TOPBP1 condensation, nucleolar DDR signaling, and rDNA repair pathway choice, and establish phase separation as a central organizing principle underlying functional specialization of the nucleolar DNA damage response.
Project description:TOPBP1 and other DNA damage response proteins play an important role in meiotic sex chromosome inactivation. We investigate a mutant mouse with a mutation in the BRCT5 domain of TOPBP1 and use single-cell RNA-seq to investigate the effect of the mutation on XY silencing.
Project description:DNA topoisomerase II-binding protein 1 (TopBP1) plays a vital role in V(D)J recombination during B and T cell development. However, its role in the development of conventional dendritic cells (cDCs) remains unexplored. Mice with DC-specific depletion of TopBP1 (TopBP1cKO) showed accelerated tumor progression due to impaired anti-tumor immunity, characterized by cDC deficiency and pre-DC accumulation. Notably, Flt3 ligand (Flt3L)-mediated tumor immunotherapy was ineffective in TopBP1cKO tumor-bearing mice. Our study demonstrates that TopBP1 is required not only for the steady-state differentiation of total cDCs, including both cDC1 and cDC2, but also for the terminal differentiation of XCR1⁻CD24⁺ emergency progenitors (EPs; CD11c⁺cKit⁺) into XCR1⁺CD24⁺ cDC1s in response to Flt3L. Furthermore, we revealed that TopBP1 directly interacts with PU.1 and IRF8, key transcription factors (TFs) required for cDC development, triggering the expression of their downstream target genes. These findings identify TopBP1 as a crucial factor for cDC development and Flt3L-driven EP differentiation into cDC1s, revealing that the function of key TFs for cDC development is mediated via interaction with TopBP1. Our work underscores the importance of TopBP1 in promoting cDC development and the therapeutic efficacy of Flt3L-mediated tumor immunotherapy.
Project description:DNA topoisomerase II-binding protein 1 (TopBP1) plays a vital role in V(D)J recombination during B and T cell development. However, its role in the development of conventional dendritic cells (cDCs) remains unexplored. Mice with DC-specific depletion of TopBP1 (TopBP1cKO) showed accelerated tumor progression due to impaired anti-tumor immunity, characterized by cDC deficiency and pre-DC accumulation. Notably, Flt3 ligand (Flt3L)-mediated tumor immunotherapy was ineffective in TopBP1cKO tumor-bearing mice. Our study demonstrates that TopBP1 is required not only for the steady-state differentiation of total cDCs, including both cDC1 and cDC2, but also for the terminal differentiation of XCR1⁻CD24⁺ emergency progenitors (EPs; CD11c⁺cKit⁺) into XCR1⁺CD24⁺ cDC1s in response to Flt3L. Furthermore, we revealed that TopBP1 directly interacts with PU.1 and IRF8, key transcription factors (TFs) required for cDC development, triggering the expression of their downstream target genes. These findings identify TopBP1 as a crucial factor for cDC development and Flt3L-driven EP differentiation into cDC1s, revealing that the function of key TFs for cDC development is mediated via interaction with TopBP1. Our work underscores the importance of TopBP1 in promoting cDC development and the therapeutic efficacy of Flt3L-mediated tumor immunotherapy.