Work by RE Workman and T Pammi from the Modell lab:

CRISPR-Cas systems provide their prokaryotic hosts with acquired immunity against viruses and other foreign genetic elements, but how these systems are regulated to prevent auto-immunity is poorly understood. In type II CRISPR-Cas systems, a transactivating CRISPR RNA (tracrRNA) scaffold functions together with a CRISPR RNA (crRNA) guide to program Cas9 for the recognition and cleavage of foreign DNA targets. Here, we show that a long-form tracrRNA performs an unexpected second function by folding into a natural single guide that directs Cas9 to transcriptionally repress its own promoter. Further, we demonstrate that Pcas9 serves as a critical regulatory node; de-repression causes a dramatic induction of Cas genes, crRNAs and tracrRNAs resulting in a 3,000-fold increase in immunization rates against unrecognized viruses. Heightened immunity comes at the cost of increased auto-immune toxicity, demonstrating the critical importance of the controller. Using a bioinformatic analysis, we provide evidence that tracrRNA-mediated autoregulation is widespread in type II CRISPR- Cas systems. Collectively, we unveil a new paradigm for the intrinsic regulation of CRISPR-Cas systems by natural single guides, which may facilitate the frequent horizontal transfer of these systems into new hosts that have not yet evolved their own regulatory strategies.

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We highlight the research of the Regot Lab:


A fundamental property of living cells is their extraordinary ability to sense and respond to a changing environment. In higher eukaryotes, malfunctioning of signaling networks has many devastating consequences such as cancer, diabetes or autoimmunity. Such consequences arise from the inability of cells to properly evaluate information and cooperate. Our main focus is to understand how individual cells use signaling networks to integrate information, and eventually coordinate collective cell behaviors.


Over the last decade, increasing evidence has shown that the stochastic nature of molecular interactions is a major challenge, especially when cells transduce environmental information. Low molecule copy numbers, macromolecular crowding and picoliter volumes shape the reality of signaling networks; a reality that is often ignored by using bulk cell-population assays. My laboratory takes a single cell approach at studying how signaling networks operate dynamically. We combine 3D live cell imaging, fluorescent biosensors and optogenetics to investigate the origins and consequences of signaling dynamics at single cell level. In particular, we concentrate in analyzing individual cells in a multicellular context where collective cell behaviors lead to complex functions, such as immune response or carcinogenesis. In developing this research program we expect to understand fundamental principles of cell signaling and multicellularity, and how they impact human disease.

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Work by Alex Paix from the Seydoux Lab:

"Homology-directed repair (HDR) of double-strand DNA breaks is a promising method for genome editing, but is thought to be less efficient than error-prone nonhomologous end joining in most cell types. We have investigated HDR of double-strand breaks induced by CRISPR-associated protein 9 (Cas9) in Caenorhabditis elegans. We find that HDR is very robust in the C. elegans germline. Linear repair templates with short (∼30-60 bases) homology arms support the integration of base and gene-sized edits with high efficiency, bypassing the need for selection. Based on these findings, we developed a systematic method to mutate, tag, or delete any gene in the C. elegans genome without the use of co-integrated markers or long homology arms. We generated 23 unique edits at 11 genes, including premature stops, whole-gene deletions, and protein fusions to antigenic peptides and GFP. Whole-genome sequencing of five edited strains revealed the presence of passenger variants, but no mutations at predicted off-target sites. The method is scalable for multi-gene editing projects and could be applied to other animals with an accessible germline."

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