Maximilian Krause’s research while affiliated with University of Bergen and other places

The design of optimal guide RNA (gRNA) sequences for CRISPR systems is challenged by the need to achieve highly efficient editing at the desired location (on‐target editing) with minimal editing at unintended locations (off‐target editing). Although laboratory validation should ideally be used to detect off‐target activity, computational predictions are almost always preferred in practice due to their speed and low cost. Several studies have therefore explored gRNA‐DNA interactions in order to understand how CRISPR complexes select their genomic targets. CHOPCHOP ( https://chopchop.cbu.uib.no/ ) leverages these developments to build a user‐friendly web interface that helps users design optimal gRNAs. CHOPCHOP supports a wide range of CRISPR applications, including gene knock‐out, sequence knock‐in, and RNA knock‐down. Furthermore, CHOPCHOP offers visualization that enables an informed choice of gRNAs and supports experimental validation. In these protocols, we describe the best practices for gRNA design using CHOPCHOP. © 2021 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1 : Design of gRNAs for gene knock‐out Alternate Protocol 1 : Design of gRNAs for dCas9 fusion/effector targeting Support Protocol : Design of gRNAs for targeting transgenic or plasmid sequences Basic Protocol 2 : Design of gRNAs for RNA targeting Basic Protocol 3 : Design of gRNAs for sequence knock‐in Alternate Protocol 2 : Design of gRNAs for knock‐in using non‐homologous end joining Basic Protocol 4 : Design of gRNAs for knock‐in using Cas9 nickases

The poly(A) tail is a homopolymeric stretch of adenosine at the 3′-end of mature RNA transcripts and its length plays an important role in nuclear export, stability, and translational regulation of mRNA. Existing techniques for genome-wide estimation of poly(A) tail length are based on short-read sequencing. These methods are limited because they sequence a synthetic DNA copy of mRNA instead of the native transcripts. Furthermore, they can identify only a short segment of the transcript proximal to the poly(A) tail which makes it difficult to assign the measured poly(A) length uniquely to a single transcript isoform. With the introduction of native RNA sequencing by Oxford Nanopore Technologies, it is now possible to sequence full-length native RNA. A single long read contains both the transcript and the associated poly(A) tail, thereby making transcriptome-wide isoform-specific poly(A) tail length assessment feasible. We developed tailfindr—an R-based package for estimating poly(A) tail length from Oxford Nanopore sequencing data. In this chapter, we describe in detail the pipeline for transcript isoform-specific poly(A) tail profiling based on native RNA Nanopore sequencing—from library preparation to downstream data analysis with tailfindr.

Translation initiation is often attributed as the rate-determining step of eukaryotic protein synthesis and key to gene expression control. Despite this centrality, the series of steps involved in this process is poorly understood. Here, we capture the transcriptome-wide occupancy of ribosomes across all stages of translation initiation, enabling us to characterize the transcriptome-wide dynamics of ribosome recruitment to mRNAs, scanning across 5′ UTRs and stop codon recognition, in a higher eukaryote. We provide mechanistic evidence for ribosomes attaching to the mRNA by threading the mRNA through the small subunit. Moreover, we identify features that regulate the recruitment and processivity of scanning ribosomes and redefine optimal initiation contexts. Our approach enables deconvoluting translation initiation into separate stages and identifying regulators at each step.

This protocol provides a detailed explanation of of the steps necessary for successful Direct RNA Library preparation for Oxford Nanopore Sequencing. The protocol explains the steps needed for RNA sample preparation based on TRIzol extraction and Poly(A)Purist Mag kit enrichment prior to Direct RNA library preparation protocol. The library preparation protocol is based on the Library preparation protocols for RNA-002 kits, yet offers additional advice on what we think is important for a successful library with minimal RNA degradation. The protocol is used to assess poly(A) tail length using the tailfindr package. The poly(A) tail is a homopolymeric stretch of adenosine at the 3`-end of mature RNA transcripts and its length plays an important role in nuclear export, stability, and translational regulation of mRNA. With the introduction of native RNA sequencing by Oxford Nanopore Technologies (ONT), it is now possible to sequence full-length native RNA. A single long read contains both the transcript and the associated poly(A) tail, thereby making genome-wide transcript-specific poly(A) tail length assessment in native RNA feasible. For more information on tailfindr visit the publication or the GitHub repository

Translation initiation is often attributed as the rate determining step of eukaryotic protein synthesis and key to gene expression control. Despite this centrality the series of steps involved in this process are poorly understood. Here we capture the transcriptome-wide occupancy of ribosomes across all stages of translation initiation, enabling us to characterize the transcriptome-wide dynamics of ribosome recruitment to mRNAs, scanning across 5'UTRs and stop codon recognition, in a higher eukaryote. We provide mechanistic evidence for ribosomes attaching to the mRNA by threading the mRNA through the small subunit. Moreover, we identify features regulating the recruitment and processivity of scanning ribosomes, redefine optimal initiation contexts and demonstrate endoplasmic reticulum specific regulation of initiation. Our approach enables deconvoluting translation initiation into separate stages and identifying the regulators at each step.

Polyadenylation at the 3'-end is a major regulator of messenger RNA and its length is known to affect nuclear export, stability, and translation, among others. Only recently have strategies emerged that allow for genome-wide poly(A) length assessment. These methods identify genes connected to poly(A) tail measurements indirectly by short-read alignment to genetic 3'-ends. Concurrently, Oxford Nanopore Technologies (ONT) established full-length isoform-specific RNA sequencing containing the entire poly(A) tail. However, assessing poly(A) length through base-calling has so far not been possible due to the inability to resolve long homopolymeric stretches in ONT sequencing. Here we present tailfindr, an R package to estimate poly(A) tail length on ONT long-read sequencing data. tailfindr operates on unaligned, base-called data. It measures poly(A) tail length from both native RNA and DNA sequencing, which makes poly(A) tail studies by full-length cDNA approaches possible for the first time. We assess tailfindr's performance across different poly(A) lengths, demonstrating that tailfindr is a versatile tool providing poly(A) tail estimates across a wide range of sequencing conditions.

The CRISPR-Cas system is a powerful genome editing tool that functions in a diverse array of organisms and cell types. The technology was initially developed to induce targeted mutations in DNA, but CRISPR-Cas has now been adapted to target nucleic acids for a range of purposes. CHOPCHOP is a web tool for identifying CRISPR-Cas single guide RNA (sgRNA) targets. In this major update of CHOPCHOP, we expand our toolbox beyond knockouts. We introduce functionality for targeting RNA with Cas13, which includes support for alternative transcript isoforms and RNA accessibility predictions. We incorporate new DNA targeting modes, including CRISPR activation/repression, targeted enrichment of loci for long-read sequencing, and prediction of Cas9 repair outcomes. Finally, we expand our results page visualization to reveal alternative isoforms and downstream ATG sites, which will aid users in avoiding the expression of truncated proteins. The CHOPCHOP web tool now supports over 200 genomes and we have released a command-line script for running larger jobs and handling unsupported genomes. CHOPCHOP v3 can be found at https://chopchop.cbu.uib.no.

Polyadenylation at the 3’-end is a major regulator of messenger RNA and its length is known to affect nuclear export, stability and translation, among others. Only recently, strategies have emerged that allow for genome-wide poly(A) length assessment. These methods identify genes connected to poly(A) tail measurements indirectly by short-read alignment to genetic 3’-ends. Concurrently Oxford Nanopore Technologies (ONT) established full-length isoform RNA sequencing containing the entire poly(A) tail. However, assessing poly(A) length through basecalling has so far not been possible due the inability to resolve long homopolymeric stretches in ONT sequencing. Here we present tailfindr , an R package to estimate poly(A) tail length on ONT long-read sequencing data. tailfindr operates on unaligned, basecalled data. It measures poly(A) tail length from both native RNA and DNA sequencing, which makes poly(A) tail studies by full-length cDNA approaches possible for the first time. We assess tailfindr’s performance across different poly(A) lengths, demonstrating that tailfindr is a versatile tool providing poly(A) tail estimates across a wide range of sequencing conditions.