Long-read sequencing for fast and robust identification of correct genome-edited alleles: PCR-based and Cas9 capture methods.

BACKGROUND: Recent developments in CRISPR/Cas9 genome-editing tools have facilitated the introduction of precise alleles, including genetic intervals spanning several kilobases, directly into the embryo. However, the introduction of donor templates, via homology directed repair, can be erroneous or incomplete and these techniques often produce mosaic founder animals. Thus, newly generated alleles must be verified at the sequence level across the targeted locus. Screening for the presence of the desired mutant allele using traditional sequencing methods can be challenging due to the size of the interval to be sequenced, together with the mosaic nature of founders. METHODOLOGY/PRINCIPAL FINDINGS: In order to help disentangle the genetic complexity of these animals, we tested the application of Oxford Nanopore Technologies long-read sequencing at the targeted locus and found that the achievable depth of sequencing is sufficient to offset the sequencing error rate associated with the technology used to validate targeted regions of interest. We have assembled an analysis workflow that facilitates interrogating the entire length of a targeted segment in a single read, to confirm that the intended mutant sequence is present in both heterozygous animals and mosaic founders. We used this workflow to compare the output of PCR-based and Cas9 capture-based targeted sequencing for validation of edited alleles. CONCLUSION: Targeted long-read sequencing supports in-depth characterisation of all experimental models that aim to produce knock-in or conditional alleles, including those that contain a mix of genome-edited alleles. PCR- or Cas9 capture-based modalities bring different advantages to the analysis.

Cleft palate and minor metabolic disturbances in a mouse global Arl15 gene knockout.

ARL15, a small GTPase protein, was linked to metabolic traits in association studies. We aimed to test the Arl15 gene as a functional candidate for metabolic traits in the mouse. CRISPR/Cas9 germline knockout (KO) of Arl15 showed that homozygotes were postnatal lethal and exhibited a complete cleft palate (CP). Also, decreased cell migration was observed from Arl15 KO mouse embryonic fibroblasts (MEFs). Metabolic phenotyping of heterozygotes showed that females had reduced fat mass on a chow diet from 14 weeks of age. Mild body composition phenotypes were also observed in heterozygous mice on a high-fat diet (HFD)/low-fat diet (LFD). Females on a HFD showed reduced body weight, gonadal fat depot weight and brown adipose tissue (BAT) weight. In contrast, in the LFD group, females showed increased bone mineral density (BMD), while males showed a trend toward reduced BMD. Clinical biochemistry analysis of plasma on HFD showed transient lower adiponectin at 20 weeks of age in females. Urinary and plasma Mg2+ concentrations were not significantly different. Our phenotyping data showed that Arl15 is essential for craniofacial development. Adult metabolic phenotyping revealed potential roles in brown adipose tissue and bone development.

CRISPR/Cas9-mediated gene knockout and interallelic gene conversion in human induced pluripotent stem cells using non-integrative bacteriophage-chimeric retrovirus-like particles.

BACKGROUND: The application of CRISPR/Cas9 technology in human induced pluripotent stem cells (hiPSC) holds tremendous potential for basic research and cell-based gene therapy. However, the fulfillment of these promises relies on the capacity to efficiently deliver exogenous nucleic acids and harness the repair mechanisms induced by the nuclease activity in order to knock-out or repair targeted genes. Moreover, transient delivery should be preferred to avoid persistent nuclease activity and to decrease the risk of off-target events. We recently developed bacteriophage-chimeric retrovirus-like particles that exploit the properties of bacteriophage coat proteins to package exogenous RNA, and the benefits of lentiviral transduction to achieve highly efficient, non-integrative RNA delivery in human cells. Here, we investigated the potential of bacteriophage-chimeric retrovirus-like particles for the non-integrative delivery of RNA molecules in hiPSC for CRISPR/Cas9 applications. RESULTS: We found that these particles efficiently convey RNA molecules for transient expression in hiPSC, with minimal toxicity and without affecting the cell pluripotency and subsequent differentiation. We then used this system to transiently deliver in a single step the CRISPR-Cas9 components (Cas9 mRNA and sgRNA) to generate gene knockout with high indel rate (up to 85%) at multiple loci. Strikingly, when using an allele-specific sgRNA at a locus harboring compound heterozygous mutations, the targeted allele was not altered by NHEJ/MMEJ, but was repaired at high frequency using the homologous wild type allele, i.e., by interallelic gene conversion. CONCLUSIONS: Our results highlight the potential of bacteriophage-chimeric retrovirus-like particles to efficiently and safely deliver RNA molecules in hiPSC, and describe for the first time genome engineering by gene conversion in hiPSC. Harnessing this DNA repair mechanism could facilitate the therapeutic correction of human genetic disorders in hiPSC.

Mice with endogenous TDP-43 mutations exhibit gain of splicing function and characteristics of amyotrophic lateral sclerosis.

TDP-43 (encoded by the gene TARDBP) is an RNA binding protein central to the pathogenesis of amyotrophic lateral sclerosis (ALS). However, how TARDBP mutations trigger pathogenesis remains unknown. Here, we use novel mouse mutants carrying point mutations in endogenous Tardbp to dissect TDP-43 function at physiological levels both in vitro and in vivo Interestingly, we find that mutations within the C-terminal domain of TDP-43 lead to a gain of splicing function. Using two different strains, we are able to separate TDP-43 loss- and gain-of-function effects. TDP-43 gain-of-function effects in these mice reveal a novel category of splicing events controlled by TDP-43, referred to as "skiptic" exons, in which skipping of constitutive exons causes changes in gene expression. In vivo, this gain-of-function mutation in endogenous Tardbp causes an adult-onset neuromuscular phenotype accompanied by motor neuron loss and neurodegenerative changes. Furthermore, we have validated the splicing gain-of-function and skiptic exons in ALS patient-derived cells. Our findings provide a novel pathogenic mechanism and highlight how TDP-43 gain of function and loss of function affect RNA processing differently, suggesting they may act at different disease stages.

A novel knockout mouse for the small EDRK-rich factor 2 (Serf2) showing developmental and other deficits.

The small EDRK-rich factor 2 (SERF2) is a highly conserved protein that modifies amyloid fibre assembly in vitro and promotes protein misfolding. However, the role of SERF2 in regulating age-related proteotoxicity remains largely unexplored due to a lack of in vivo models. Here, we report the generation of Serf2 knockout mice using an ES cell targeting approach, with Serf2 knockout alleles being bred onto different defined genetic backgrounds. We highlight phenotyping data from heterozygous Serf2+/- mice, including unexpected male-specific phenotypes in startle response and pre-pulse inhibition. We report embryonic lethality in Serf2-/- null animals when bred onto a C57BL/6 N background. However, homozygous null animals were viable on a mixed genetic background and, remarkably, developed without obvious abnormalities. The Serf2 knockout mice provide a powerful tool to further investigate the role of SERF2 protein in previously unexplored pathophysiological pathways in the context of a whole organism.

Application of long single-stranded DNA donors in genome editing: generation and validation of mouse mutants.

BACKGROUND: Recent advances in clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) genome editing have led to the use of long single-stranded DNA (lssDNA) molecules for generating conditional mutations. However, there is still limited available data on the efficiency and reliability of this method. RESULTS: We generated conditional mouse alleles using lssDNA donor templates and performed extensive characterization of the resulting mutations. We observed that the use of lssDNA molecules as donors efficiently yielded founders bearing the conditional allele, with seven out of nine projects giving rise to modified alleles. However, rearranged alleles including nucleotide changes, indels, local rearrangements and additional integrations were also frequently generated by this method. Specifically, we found that alleles containing unexpected point mutations were found in three of the nine projects analyzed. Alleles originating from illegitimate repairs or partial integration of the donor were detected in eight projects. Furthermore, additional integrations of donor molecules were identified in four out of the seven projects analyzed by copy counting. This highlighted the requirement for a thorough allele validation by polymerase chain reaction, sequencing and copy counting of the mice generated through this method. We also demonstrated the feasibility of using lssDNA donors to generate thus far problematic point mutations distant from active CRISPR cutting sites by targeting two distinct genes (Gckr and Rims1). We propose a strategy to perform extensive quality control and validation of both types of mouse models generated using lssDNA donors. CONCLUSION: lssDNA donors reproducibly generate conditional alleles and can be used to introduce point mutations away from CRISPR/Cas9 cutting sites in mice. However, our work demonstrates that thorough quality control of new models is essential prior to reliably experimenting with mice generated by this method. These advances in genome editing techniques shift the challenge of mutagenesis from generation to the validation of new mutant models.

Induced Pluripotent Stem Cells for Primary Ciliary Dyskinesia Modeling and Personalized Medicine.

Primary ciliary dyskinesia (PCD) is a rare and heterogeneous genetic disorder that affects the structure and function of motile cilia. In the airway epithelium, impaired ciliary motion results in reduced or absent mucociliary clearance that leads to the appearance of chronic airway infection, sinusitis, and bronchiectasis. Currently, there is no effective treatment for PCD, and research is limited by the lack of convenient models to study this disease and investigate innovative therapies. Furthermore, the high heterogeneity of PCD genotypes is likely to hinder the development of a single therapy for all patients. The generation of patient-derived, induced pluripotent stem cells, and their differentiation into airway epithelium, as well as genome editing technologies, could represent major tools for in vitro PCD modeling and for developing personalized therapies. Here, we review PCD pathogenesis and then discuss how human induced pluripotent stem cells could be used to model this disease for the development of innovative, patient-specific biotherapies.

Analysing the outcome of CRISPR-aided genome editing in embryos: Screening, genotyping and quality control.

The application of CRISPR/Cas9 technology has revolutionised genetics by greatly enhancing the efficacy of genome editing in the early embryo. Furthermore, the system has enabled the generation of allele types previously incompatible with in vivo mutagenesis. Despite its versatility and ease of implementation, CRISPR/Cas9 editing outcome is unpredictable and can generate mosaic founders. Therefore, careful genotyping and characterisation of new mutants is proving essential. The literature presents a wide range of protocols for molecular characterisation, each representing different levels of investment. We present strategies and protocols for designing, producing and screening CRISPR/Cas9 edited founders and genotyping their offspring according to desired allele type (indel, point mutation and deletion).

Aneuploidy screening of embryonic stem cell clones by metaphase karyotyping and droplet digital polymerase chain reaction.

BACKGROUND: Karyotypic integrity is essential for the successful germline transmission of alleles mutated in embryonic stem (ES) cells. Classical methods for the identification of aneuploidy involve cytological analyses that are both time consuming and require rare expertise to identify mouse chromosomes. RESULTS: As part of the International Mouse Phenotyping Consortium, we gathered data from over 1,500 ES cell clones and found that the germline transmission (GLT) efficiency of clones is compromised when over 50 % of cells harbour chromosome number abnormalities. In JM8 cells, chromosomes 1, 8, 11 or Y displayed copy number variation most frequently, whilst the remainder generally remain unchanged. We developed protocols employing droplet digital polymerase chain reaction (ddPCR) to accurately quantify the copy number of these four chromosomes, allowing efficient triage of ES clones prior to microinjection. We verified that assessments of aneuploidy, and thus decisions regarding the suitability of clones for microinjection, were concordant between classical cytological and ddPCR-based methods. Finally, we improved the method to include assay multiplexing so that two unstable chromosomes are counted simultaneously (and independently) in one reaction, to enhance throughput and further reduce the cost. CONCLUSION: We validated a PCR-based method as an alternative to classical karyotype analysis. This technique enables laboratories that are non-specialist, or work with large numbers of clones, to precisely screen ES cells for the most common aneuploidies prior to microinjection to ensure the highest level of germline transmission potential. The application of this method allows early exclusion of aneuploid ES cell clones in the ES cell to mouse conversion process, thus improving the chances of obtaining germline transmission and reducing the number of animals used in failed microinjection attempts. This method can be applied to any other experiments that require accurate analysis of the genome for copy number variation (CNV).

Generation of a healthy heavy smoker patient-derived induced pluripotent stem cell line UHOMi007-A from peripheral blood mononuclear cells.

Human pluripotent stem cells (hiPSC) represent a unique opportunity to model lung development and chronic bronchial diseases. We generated a hiPSC line from a highly characterized healthy heavy smoker male donor free from emphysema or tobacco related disease. Peripheral blood mononuclear cells (PBMCs) were reprogrammed using integration-free Sendai virus. The cell line had normal karyotype, expressed pluripotency hallmarks, and differentiated into the three primary germ layers. The reported UHOMi007-A iPSC line may be used as a control to model lung development, study human chronic bronchial diseases and drug testing.

Differentiation of Human Induced Pluripotent Stem Cells from Patients with Severe COPD into Functional Airway Epithelium.

Background: Chronic Obstructive Pulmonary Disease (COPD), a major cause of mortality and disability, is a complex disease with heterogeneous and ill-understood biological mechanisms. Human induced pluripotent stem cells (hiPSCs) are a promising tool to model human disease, including the impact of genetic susceptibility. Methods: We developed a simple and reliable method for reprogramming peripheral blood mononuclear cells into hiPSCs and to differentiate them into air−liquid interface bronchial epithelium within 45 days. Importantly, this method does not involve any cell sorting step. We reprogrammed blood cells from one healthy control and three patients with very severe COPD. Results: The mean cell purity at the definitive endoderm and ventral anterior foregut endoderm (vAFE) stages was >80%, assessed by quantifying C-X-C Motif Chemokine Receptor 4/SRY-Box Transcription Factor 17 (CXCR4/SOX17) and NK2 Homeobox 1 (NKX2.1) expression, respectively. vAFE cells from all four hiPSC lines differentiated into bronchial epithelium in air−liquid interface conditions, with large zones covered by beating ciliated, basal, goblets, club cells and neuroendocrine cells, as found in vivo. The hiPSC-derived airway epithelium (iALI) from patients with very severe COPD and from the healthy control were undistinguishable. Conclusions: iALI bronchial epithelium is ready for better understanding lung disease pathogenesis and accelerating drug discovery.

Generation of four severe early-onset chronic obstructive pulmonary disease (COPD) patient-derived induced pluripotent stem cell lines from peripheral blood mononuclear cells.

Evidence highlights the concept of multiple trajectories leading to COPD. Early-life events (i.e., in utero lung development) may influence the maximally attained lung function and increase the risk to develop COPD. Human pluripotent stem cells (hiPSC) represent a unique opportunity to model lung development. We generated hiPSC lines from four highly characterized COPD patients with early onset and severe phenotype. Peripheral blood mononuclear cells (PBMCs) were reprogrammed using integration-free Sendai Virus. The cell lines had normal karyotype, expressed pluripotency hallmarks, and differentiated into the three primary germ layers. These lines offer a tool to study early-life origins of COPD.

Linking the FTO obesity rs1421085 variant circuitry to cellular, metabolic, and organismal phenotypes in vivo.

Variants in FTO have the strongest association with obesity; however, it is still unclear how those noncoding variants mechanistically affect whole-body physiology. We engineered a deletion of the rs1421085 conserved cis-regulatory module (CRM) in mice and confirmed in vivo that the CRM modulates Irx3 and Irx5 gene expression and mitochondrial function in adipocytes. The CRM affects molecular and cellular phenotypes in an adipose depot-dependent manner and affects organismal phenotypes that are relevant for obesity, including decreased high-fat diet-induced weight gain, decreased whole-body fat mass, and decreased skin fat thickness. Last, we connected the CRM to a genetically determined effect on steroid patterns in males that was dependent on nutritional challenge and conserved across mice and humans. Together, our data establish cross-species conservation of the rs1421085 regulatory circuitry at the molecular, cellular, metabolic, and organismal level, revealing previously unknown contextual dependence of the variant's action.

Targeted Mutations in the Mouse via Embryonic Stem Cells.

Genetic modification of mouse embryonic stem (ES) cells is a powerful technology that enabled the generation of a plethora of mutant mouse lines to study gene function and mammalian biology. Here we describe ES cell culture and transfection techniques used to manipulate the ES cell genome to obtain targeted ES cell clones. We include the standard gene targeting approach as well as the application of the CRISPR/Cas9 system that can improve the efficiency of homologous recombination in ES cells by introducing a double-strand DNA break at the target site.

Pipeline for the Generation and Characterization of Transgenic Human Pluripotent Stem Cells Using the CRISPR/Cas9 Technology.

Recent advances in genome engineering based on the CRISPR/Cas9 technology have revolutionized our ability to manipulate genomic DNA. Its use in human pluripotent stem cells (hPSCs) has allowed a wide range of mutant cell lines to be obtained at an unprecedented rate. The combination of these two groundbreaking technologies has tremendous potential, from disease modeling to stem cell-based therapies. However, the generation, screening and molecular characterization of these cell lines remain a cumbersome and multi-step endeavor. Here, we propose a pipeline of strategies to efficiently generate, sub-clone, and characterize CRISPR/Cas9-edited hPSC lines in the function of the introduced mutation (indels, point mutations, insertion of large constructs, deletions).

Generation of the induced pluripotent stem cell line UHOMi002-A from peripheral blood mononuclear cells of a healthy male donor.

Human pluripotent stem cells (hiPSC) are highly valuable tools to model lung development and chronic bronchial diseases. We generated a hiPSC line from a highly characterized 40-year-old healthy male nonsmoking donor. Peripheral blood mononuclear cells (PBMCs) were reprogrammed using integration-free Sendai Virus. The cell line had normal karyotype, expressed pluripotency hallmarks, and differentiated into the three primary germ layers. The reported UHOMi002-A iPSC line may be used as a control to model lung development, study human chronic bronchial diseases and drug testing.

[Lung organoids]. / Les organoïdes pulmonaires.

As burden of chronic respiratory diseases is constantly increasing, improving in vitro lung models is essential in order to reproduce as closely as possible the complex pulmonary architecture, responsible for oxygen uptake and carbon dioxide clearance. The study of diseases that affect the respiratory system has benefited from in vitro reconstructions of the respiratory epithelium with inserts in air/liquid interface (2D) or in organoids able to mimic up to the arborescence of the respiratory tree (3D). Recent development in the fields of pluripotent stem cells-derived organoids and genome editing technologies has provided new insights to better understand pulmonary diseases and to find new therapeutic perspectives.

TITLE: Les organoïdes pulmonaires. ABSTRACT: L'impact en santé publique des pathologies respiratoires chroniques ne cesse de croître. Dans ce contexte, il paraît indispensable d'améliorer les modèles d'études du poumon afin de reproduire au plus proche l'architecture pulmonaire complexe, garante des fonctions d'oxygénation et d'épuration du gaz carbonique. Les connaissances actuelles en physiopathologie respiratoire résultent en partie des études de modèles de reconstitution d'épithélium bronchique in vitro à partir de cellules primaires, en deux dimensions sur des inserts, ou en trois dimensions, en organoïdes mimant jusqu'à l'arborescence pulmonaire. Le développement de ces modèles in vitro a connu un nouvel essor grâce aux organoïdes pulmonaires issus de cellules souches pluripotentes et la démocratisation des outils d'édition du génome. Ces apports technologiques récents offrent de nouvelles perspectives en matière de thérapeutiques ou de compréhension physiopathologique et pourraient, dans le futur, ouvrir les portes de la médecine régénératrice pulmonaire.

Recurrent Genetic Abnormalities in Human Pluripotent Stem Cells: Definition and Routine Detection in Culture Supernatant by Targeted Droplet Digital PCR.

Genomic integrity of human pluripotent stem cells (hPSCs) is essential for research and clinical applications. However, genetic abnormalities can accumulate during hPSC generation and routine culture and following gene editing. Their occurrence should be regularly monitored, but the current assays to assess hPSC genomic integrity are not fully suitable for such regular screening. To address this issue, we first carried out a large meta-analysis of all hPSC genetic abnormalities reported in more than 100 publications and identified 738 recurrent genetic abnormalities (i.e., overlapping abnormalities found in at least five distinct scientific publications). We then developed a test based on the droplet digital PCR technology that can potentially detect more than 90% of these hPSC recurrent genetic abnormalities in DNA extracted from culture supernatant samples. This test can be used to routinely screen genomic integrity in hPSCs.

Male mice lacking ADAMTS-16 are fertile but exhibit testes of reduced weight.

Adamts16 encodes a disintegrin-like and metalloproteinase with thrombospondin motifs, 16, a member of a family of multi-domain, zinc-binding proteinases. ADAMTS-16 is implicated in a number of pathological conditions, including hypertension, cancer and osteoarthritis. A large number of observations, including a recent report of human ADAMTS16 variants in cases of 46,XY disorders/differences of sex development (DSD), also implicate this gene in human testis determination. We used CRISPR/Cas9 genome editing to generate a loss-of-function allele in the mouse in order to examine whether ADAMTS-16 functions in mouse testis determination or testicular function. Male mice lacking Adamts16 on the C57BL/6N background undergo normal testis determination in the fetal period. However, adult homozygotes have an average testis weight that is around 10% lower than age-matched controls. Cohorts of mutant males tested at 3-months and 6-months of age were fertile. We conclude that ADAMTS-16 is not required for testis determination or male fertility in mice. We discuss these phenotypic data and their significance for our understanding of ADAMTS-16 function.

Generation of the induced pluripotent stem cell line UHOMi001-A from a patient with mutations in CCDC40 gene causing Primary Ciliary Dyskinesia (PCD).

Primary Ciliary Dyskinesia (PCD) is a rare heterogeneous genetic disorder affecting motile cilia structure and function leading to lung disease. We generated induced pluripotent stem cells (iPSCs) from dermal fibroblasts of a female PCD patient carrying disease-causing variants in the CCDC40 gene. Reprogramming was performed with the human OSKM transcription factors using the Sendai-virus delivery system. The resulting transgene free iPSCs had normal karyotype, expressed pluripotency markers, could differentiate into the three germ layers in vivo and retained the disease-causing CCDC40 mutations. This iPSC line could be useful to model PCD disease and test gene therapy strategies. Resource Table.