Quantitative insertion-site sequencing (QIseq) for high throughput phenotyping of transposon mutants.

Genetic screening using random transposon insertions has been a powerful tool for uncovering biology in prokaryotes, where whole-genome saturating screens have been performed in multiple organisms. In eukaryotes, such screens have proven more problematic, in part because of the lack of a sensitive and robust system for identifying transposon insertion sites. We here describe quantitative insertion-site sequencing, or QIseq, which uses custom library preparation and Illumina sequencing technology and is able to identify insertion sites from both the 5' and 3' ends of the transposon, providing an inbuilt level of validation. The approach was developed using piggyBac mutants in the human malaria parasite Plasmodium falciparum but should be applicable to many other eukaryotic genomes. QIseq proved accurate, confirming known sites in >100 mutants, and sensitive, identifying and monitoring sites over a >10,000-fold dynamic range of sequence counts. Applying QIseq to uncloned parasites shortly after transfections revealed multiple insertions in mixed populations and suggests that >4000 independent mutants could be generated from relatively modest scales of transfection, providing a clear pathway to genome-scale screens in P. falciparum QIseq was also used to monitor the growth of pools of previously cloned mutants and reproducibly differentiated between deleterious and neutral mutations in competitive growth. Among the mutants with fitness defects was a mutant with a piggyBac insertion immediately upstream of the kelch protein K13 gene associated with artemisinin resistance, implying mutants in this gene may have competitive fitness costs. QIseq has the potential to enable the scale-up of piggyBac-mediated genetics across multiple eukaryotic systems.

Combined Genome and Transcriptome (G&T) Sequencing of Single Cells.

The simultaneous examination of a single cell's genome and transcriptome presents scientists with a powerful tool to study genetic variability and its effect on gene expression. In this chapter, we describe the library generation method for combined genome and transcriptome sequencing (G&T-seq) originally described by Macaulay et al. (Nat Protoc 11(11):2081-2103, 2016; Nat Methods 12(6):519-522, 2015). This includes some alterations we made to improve robustness of this process for both the novice user and laboratories that want to deploy this method at scale. Using this method, genomic DNA and full-length mRNA from single cells are separated, amplified, and converted into Illumina sequencer-compatible sequencing libraries.

Best Practices for Illumina Library Preparation.

In this unit, we describe a set of protocols and recommendations for Illumina library preparation. We review best practices in template quantitation methods; template fragmentation methodologies; solid-phase reverse-immobilization cleanup, including buffer exchange and size selection; end repair, A-tailing, and adapter ligation; indexing strategies; considerations regarding whether to use polymerase chain reaction; final library quantification methodologies; and normalization and pooling strategies. These workflows are applicable to both high-throughput and low-throughput Illumina library preparation and should help reduce bias, increase cost effectiveness, and produce high library yields. This is an extensive update of the previous version of this unit. © 2019 by John Wiley & Sons, Inc.

PiggyBac Transposon-Based Insertional Mutagenesis in Mice.

While sequencing and array-based studies are creating catalogues of genetic alterations in cancer, discriminating cancer drivers among the large sets of epigenetically, transcriptionally or posttranslationally dysregulated genes remains a challenge. Transposon-based genetic screening in mice has proven to be a powerful approach to address this challenge. Insertional mutagenesis directly flags biologically relevant genes and, combined with the transposon's unique molecular fingerprint, facilitates the recovery of insertion sites. We have generated transgenic mouse lines harboring different versions of PiggyBac-based oncogenic transposons, which in conjunction with PiggyBac transposase mice can be used for whole-body or tissue-specific insertional mutagenesis screens. We have also developed QiSeq, a method for (semi-)quantitative transposon insertion site sequencing, which overcomes biasing limitations of previous library preparation methods. QiSeq can be used in multiplexed high-throughput formats for candidate cancer gene discovery and gives insights into the clonal distribution of insertions for the study of genetic tumor evolution.

Assembly of transgenic human P301S Tau is necessary for neurodegeneration in murine spinal cord.

A pathological pathway leading from soluble monomeric to insoluble filamentous Tau is characteristic of many human neurodegenerative diseases, which also exhibit dysfunction and death of brain cells. However, it is unknown how the assembly of Tau into filaments relates to cell loss. To study this, we first used a mouse line transgenic for full-length human mutant P301S Tau to investigate the temporal relationship between Tau assembly into filaments, assessed using anti-Tau antibody AT100, and motor neuron numbers, in the lumbar spinal cord. AT100 immunoreactivity preceded nerve cell loss. Murine Tau did not contribute significantly to either Tau aggregation or neurodegeneration. To further study the relevance of filament formation for neurodegeneration, we deleted hexapeptides 275VQIINK280 and 306VQIVYK311, either singly or in combination, from human 0N4R Tau with the P301S mutation. These hexapeptides are essential for the assembly of Tau into filaments. Homozygous mice transgenic for P301S Tau with the hexapeptide deletions, which expressed Tau at a similar level to the heterozygous line transgenic for P301S Tau, had a normal lifespan, unlike mice from the P301S Tau line. The latter had significant levels of sarkosyl-insoluble Tau in brain and spinal cord, and exhibited neurodegeneration. Mice transgenic for P301S Tau with the hexapeptide deletions failed to show significant levels of sarkosyl-insoluble Tau or neurodegeneration. Recombinant P301S Tau with the hexapeptide deletions failed to form ß-sheet structure and filaments following incubation with heparin. Taken together, we conclude that ß-sheet assembly of human P301S Tau is necessary for neurodegeneration in transgenic mice.

Uncovering the essential genes of the human malaria parasite Plasmodium falciparum by saturation mutagenesis.

Severe malaria is caused by the apicomplexan parasite Plasmodium falciparum. Despite decades of research, the distinct biology of these parasites has made it challenging to establish high-throughput genetic approaches to identify and prioritize therapeutic targets. Using transposon mutagenesis of P. falciparum in an approach that exploited its AT-rich genome, we generated more than 38,000 mutants, saturating the genome and defining mutability and fitness costs for over 87% of genes. Of 5399 genes, our study defined 2680 genes as essential for optimal growth of asexual blood stages in vitro. These essential genes are associated with drug resistance, represent leading vaccine candidates, and include approximately 1000 Plasmodium-conserved genes of unknown function. We validated this approach by testing proteasome pathways for individual mutants associated with artemisinin sensitivity.

The DeltaK280 mutation in MAP tau favors exon 10 skipping in vivo.

Tau mutations in frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) are associated with changes in alternative splicing of exon 10. The DeltaK280 mutation in exon 10 is exceptional because in vitro observations suggest a dramatic effect on microtubule binding, enhanced self-aggregation, as well as a decrease of the 4R/3R ratio by the ablation of an exon splicing enhancer element. Using immunohistochemistry, Western blotting, and electron microscopy on brain material with the DeltaK280 mutation, we investigated which of these effects is most dominant in vivo. The brain showed abundant Pick bodies in several brain regions, which stained positive with 3-repeat-specific but not with 4-repeat-specific tau antibodies. Western blots of sarkosyl-insoluble tau showed exclusively three repeat (3R0N and 3R1N) tau in most regions, although some 4R1N could be detected in the frontal cortex. In addition, the sarkosyl-soluble tau fraction showed a significantly higher amount of 3-repeat tau. Because quantitative analysis of 4R and 3R mRNA transcripts showed a 4R/3R ratio of only 0.3, association between increased transcription and protein expression was observed. These observations confirm the postulated hypothesis that the DeltaK280 mutation abolishes a splice enhancer element, which overrules the decreased microtubule binding and enhanced self-aggregation.

Progranulin mutations in Dutch familial frontotemporal lobar degeneration.

Mutations in the progranulin (PGRN) gene have recently been identified in frontotemporal lobar degeneration with ubiquitin inclusions linked to chromosome 17q21. We report here the finding of two novel frameshift mutations and three possible pathogenic missense mutations in the PGRN gene. Furthermore, we determined the frequency of PGRN mutations in familial cases recruited from a large population-based study of frontotemporal lobar degeneration carried out in The Netherlands.

Genome-wide transposon screening and quantitative insertion site sequencing for cancer gene discovery in mice.

Transposon-mediated forward genetics screening in mice has emerged as a powerful tool for cancer gene discovery. It pinpoints cancer drivers that are difficult to find with other approaches, thus complementing the sequencing-based census of human cancer genes. We describe here a large series of mouse lines for insertional mutagenesis that are compatible with two transposon systems, PiggyBac and Sleeping Beauty, and give guidance on the use of different engineered transposon variants for constitutive or tissue-specific cancer gene discovery screening. We also describe a method for semiquantitative transposon insertion site sequencing (QiSeq). The QiSeq library preparation protocol exploits acoustic DNA fragmentation to reduce bias inherent to widely used restriction-digestion-based approaches for ligation-mediated insertion site amplification. Extensive multiplexing in combination with next-generation sequencing allows affordable ultra-deep transposon insertion site recovery in high-throughput formats within 1 week. Finally, we describe principles of data analysis and interpretation for obtaining insights into cancer gene function and genetic tumor evolution.

A conditional piggyBac transposition system for genetic screening in mice identifies oncogenic networks in pancreatic cancer.

Here we describe a conditional piggyBac transposition system in mice and report the discovery of large sets of new cancer genes through a pancreatic insertional mutagenesis screen. We identify Foxp1 as an oncogenic transcription factor that drives pancreatic cancer invasion and spread in a mouse model and correlates with lymph node metastasis in human patients with pancreatic cancer. The propensity of piggyBac for open chromatin also enabled genome-wide screening for cancer-relevant noncoding DNA, which pinpointed a Cdkn2a cis-regulatory region. Histologically, we observed different tumor subentities and discovered associated genetic events, including Fign insertions in hepatoid pancreatic cancer. Our studies demonstrate the power of genetic screening to discover cancer drivers that are difficult to identify by other approaches to cancer genome analysis, such as downstream targets of commonly mutated human cancer genes. These piggyBac resources are universally applicable in any tissue context and provide unique experimental access to the genetic complexity of cancer.

Improved Protocols for Illumina Sequencing.

In this unit, we describe a set of improvements that have been made to the standard Illumina protocols to make the sequencing process more reliable in a high-throughput environment, reduce amplification bias, narrow the distribution of insert sizes, and reliably obtain high yields of data.

Comprehensive mRNA expression profiling distinguishes tauopathies and identifies shared molecular pathways.

BACKGROUND: Understanding the aetiologies of neurodegenerative diseases such as Alzheimer's disease (AD), Pick's disease (PiD), Progressive Supranuclear Palsy (PSP) and Frontotemporal dementia (FTD) is often hampered by the considerable clinical and molecular overlap between these diseases and normal ageing. The development of high throughput genomic technologies such as microarrays provide a new molecular tool to gain insight in the complexity and relationships between diseases, as they provide data on the simultaneous activity of multiple genes, gene networks and cellular pathways. METHODOLOGY/PRINCIPAL FINDINGS: We have constructed genome wide expression profiles from snap frozen post-mortem tissue from the medial temporal lobe of patients with four neurodegenerative disorders (5 AD, 5 PSP, 5 PiD and 5 FTD patients) and 5 control subjects. All patients were matched for age, gender, ApoE-epsilon and MAPT (tau) haplotype. From all groups a total of 790 probes were shown to be differently expressed when compared to control individuals. The results from these experiments were then used to investigate the correlations between clinical, pathological and molecular findings. From the 790 identified probes we extracted a gene set of 166 probes whose expression could discriminate between these disorders and normal ageing. CONCLUSIONS/SIGNIFICANCE: From genome wide expression profiles we extracted a gene set of 166 probes whose expression could discriminate between neurological disorders and normal ageing. This gene set can be further developed into an accurate microarray-based classification test. Furthermore, from this dataset we extracted a disease specific set of genes and identified two aging related transcription factors (FOXO1A and FOXO3A) as possible drug targets related to neurodegenerative disease.

The DJ-1L166P mutant protein associated with early onset Parkinson's disease is unstable and forms higher-order protein complexes.

Parkinson's disease (PD) is a common neurodegenerative disorder that involves the selective degeneration of midbrain dopaminergic neurons. Recently DJ-1 mutations have been linked to autosomal-recessive early-onset Parkinsonism in two European families. By using gel filtration assays under physiological conditions we demonstrate that DJ-1 protein forms a dimeric structure. Conversely, the DJ-1L166P mutant protein shows a different elution profile as compared with DJ-1WT both in overexpression cellular systems or in lymphoblasts cells, suggesting that it might form higher order protein structures. Furthermore we observed that the level of DJ-1L166P mutant protein in the patient's lymphoblasts was very low as compared with the wild-type protein. We excluded a potential transcriptional impairment by performing quantitative RT-PCR on the patient's material. Pulse-chase experiments in transfected COS-1 cells and cycloheximide treatment in control and patient lymphoblasts indicated that the mutant protein was rapidly degraded. This rapid turnover and the structural changes of DJ-1L166P mutant protein might be crucial in the disease pathogenesis.