Project description:Nonsense-mediated decay (NMD) is a pathway that degrades messenger RNAs containing premature termination codons. Here, a genome-wide screen for NMD factors uncovered an unexpected mechanism that broadly governs 3ʹ untranslated region (UTR)-directed regulation. The screen revealed that NMD requires lysosomal acidification, which allows transferrin-mediated iron uptake, which in turn is necessary for iron-sulfur (Fe-S) cluster biogenesis. This pathway converges on the Fe-S cluster-containing ribosome recycling factor ABCE1, whose impaired function results in the movement of ribosomes into 3ʹ UTRs where they displace exon junction complexes, thereby abrogating NMD. Importantly, these effects extend beyond NMD substrates, with ABCE1 activity required to maintain the accessibility of 3ʹ UTRs to diverse regulators, including microRNAs and RNA binding proteins. Due to the sensitivity of the Fe-S cluster of ABCE1 to iron availability and reactive oxygen species, these findings reveal an unanticipated vulnerability of 3ʹ UTR-directed regulation to lysosomal dysfunction, iron deficiency, and oxidative stress.
Project description:To search for factors regulating neuronal differentiation, we performed a genome-wide loss-of-function CRISPR/Cas9 screen in haploid human ESCs. The regulators were identified by the quantification of depletion of their mutant clones within a pooled loss-of-function library upon neuronal differentiation.
Project description:We performed a FACS-based genome-wide CRISPR knockout screen in primary murine macrophages to identify regulators of efferocytosis, the phagocytic clearance of dying cells. The screen identified known and novel regulators of macrophage efferocytosis. More broadly, the screen approach can be applied to interrogate complex functional phenotypes in primary macrophages.
Project description:Proinsulin is the precursor of insulin in pancreatic beta cells. Altered proinsulin and proinsulin to insulin ratio mark beta cell dysfunction, predictuing disease progression into type 1 and type 2 diabetes. Of essential role for beta cell function, knowledge about proinsulin production and its role in disease are currently very limited. Using genome wide CRISPR screen, we identified 84 proinsulin regulators including classical protein convertases Pcsk1 and Cpe, and novel factors like Pdia6. Among the list 29 proinsulin regulators were trajectory genes involved in disease progression in obesity and type 2 diabetes in humans. In vivo mouse genetics study revealed unique genetic architecture and quantitative trait loci (QTLs) modulating plasma proinsulin levels. Integrative analyzing and mapping of the QTL signals directly pinpointed to proinsulin regulators identified from the CRISPR screen, which in return greatly improved resolution of the mouse genetic study. 4 out of 5 overlapped genes can be individually validated. Knocking down the leading hits Pdia6 leads to decreased proinsulin content and remarkable loss of proinsulin granules in beta cells. Consequently, proinsulin secretion was greatly decreased. Mechanistically, protein translation rate was greatly impaired after knocking down Pdia6. Our study demonstrated the power of combining in vitro functional genomics with in vivo mouse genetics study to identify proinsulin regulatory network in pancreatic beta cells.
Project description:Translation of messenger RNAs (mRNAs) with premature translation termination codons produces truncated proteins with potentially deleterious effects. This is prevented by nonsense-mediated mRNA decay (NMD) of these mRNAs. NMD is triggered by ribosomes terminating upstream of a splice site marked by an exon-junction complex (EJC), but also acts on many mRNAs lacking a splice junction after their termination codon. We developed a genome-wide CRISPR flow cytometry screen to identify regulators of mRNAs with premature termination codons in K562 cells. This screen recovered essentially all core NMD factors and suggested a role for EJC factors in degradation of PTCs without downstream splicing. Among the strongest hits were the translational repressors GIGYF2 and EIF4E2. GIGYF2 and EIF4E2 mediate translational repression but not mRNA decay of a subset of NMD targets and interact with NMD factors genetically and physically. Our results suggest a model wherein recognition of a stop codon as premature can lead to its translational repression through GIGYF2 and EIF4E2.
Project description:A genome-wide CRISPR screen was combined with a tdTomato reporter-based epigenetic memory assay to identify factors that erase epigenetic memory in ESC. After introducing genome wide perturbation and dCas9::KRAB-mediated epigenetic editing of the Esg1-tdTomato reporter, the trigger was released and cells that maintained the silencing sorted at FACS. Samples were collected out of sorted tdTomato negative (TOMminus) and positive (TOMplus) cells after 6 days of DOX treatment (epigenetic editing) and 3 or 7 days of DOX washout (release of the trigger), using a gating strategy to separate the bottom 2.5% negative cells (2.5%gate) and cells ranging from mildly to fully repressed (widegate).
Project description:To search for host factors regulating Zika virus infection, we performed a genome-wide loss-of-function CRISPR/Cas9 screen in haploid human ESCs. The regulators were identified by the quantification of enrichment of their mutant clones within a pooled loss-of-function library upon Zika virus infection.
Project description:Genome-wide CRISPR-Cas9 knockout screen using TKOv1 sgRNA library was performed in isogenic RBM10-proficient and RBM10-deficient HCC827 cells.