Biology subjects

Dickinson, M. E.

Publications and source records attributed to Dickinson, M. E..

8 recordsLinked to original sources

bioRxiv2024

A Comprehensive Atlas of AAV Tropism in the Mouse

Gene therapy with Adeno-Associated Viral (AAV) vectors requires knowledge of their tropism within the body. Here we analyze the tropism of ten naturally occurring AAV serotypes (AAV3B, AAV4, AAV5, AAV6, AAV7, AAV8, AAV9, AAVrh8, AAVrh10 and AAVrh74) following systemic delivery into male and female mice. A transgene expressing ZsGreen and Cre recombinase was used to identify transduction in a cell-dependent manner based on fluorescence. Cre-driven activation of tdTomato fluorescence offered superior sensitivity for transduced cells. All serotypes except AAV3B and AAV4 had high liver tropism. Fluorescence activation revealed transduction of unexpected tissues, including adrenals, testes and ovaries. Rare transduced cells within tissues were also readily visualized. Biodistribution of AAV genomes correlated with fluorescence, except in immune tissues. AAV4 was found to have a pan-endothelial tropism while also targeting pancreatic beta cells. This public resource enables selection of the best AAV serotypes for basic science and preclinical applications in mice.

molecular biology↗

bioRxiv2022

EZ Clear for simple, rapid, and robust mouse whole organ clearing

Tissue clearing for whole organ cell profiling has revolutionized biology and imaging for exploration of organs in three-dimensional space without compromising tissue architecture. But complicated, laborious procedures, or expensive equipment, as well as the use of hazardous, organic solvents prevents the widespread adoption of these methods. Here we report a simple and rapid tissue clearing method, EZ Clear, that can clear whole adult mouse organs in 48 hours in just three simple steps. Samples stay at room temperature and remain hydrated throughout the clearing process, preserving endogenous and synthetic fluorescence, without altering sample size. After wholemount clearing and imaging, EZ Cleared samples can be further processed for downstream embedding and cryosectioning followed by standard histology or immunostaining, without loss of endogenous or synthetic fluorescence signal. Overall, the simplicity, speed, and flexibility of EZ Clear make it easy to adopt and apply to diverse approaches in biomedical research.

developmental biology↗

bioRxiv2021

The production of 4,182 mouse lines identifies experimental and biological variables impacting Cas9-mediated mutant mouse line production

The International Mouse Phenotyping Consortium (IMPC) systematically produces and phenotypes mouse lines with presumptive null mutations to provide insight into gene function. The IMPC now uses the programmable RNA-guided nuclease Cas9 for its increased capacity and flexibility to efficiently generate null alleles in the C57BL/6N strain. In addition to being a valuable novel and accessible research resource, the production of 3,313 knockout mouse lines using comparable protocols provides a rich dataset to analyze experimental and biological variables affecting in vivo gene engineering with Cas9. Mouse line production has two critical steps - generation of founders with the desired allele and germline transmission (GLT) of that allele from founders to offspring. A systematic evaluation of the variables impacting success rates identified gene essentiality as the primary factor influencing successful production of null alleles. Collectively, our findings provide best practice recommendations for using Cas9 to generate alleles in mouse essential genes, many of which are orthologs of genes linked to human disease.

genetics↗

bioRxiv2021

FOXO1 represses Sprouty2 and Sprouty4 expressionin endothelial cells to promote arterial specification and vascular remodeling in the mouse yolk sac

The establishment of a functional circulatory system is required for post-implantation development during murine embryogenesis. Previous studies in loss of function mouse models have shown that FOXO1, a Forkhead family transcription factor, is required for yolk sac vascular remodeling and survival beyond embryonic day (E) 11. Here, we demonstrate that loss of FoxO1 in E8.25 endothelial cells results in increased Sprouty2 and Sprouty4 transcripts, reduced expression of arterial genes, and decreased Flk1/Vegfr2 mRNA levels without affecting overall endothelial cell identity, survival, or proliferation. Using a Dll4-BAC-nlacZ reporter line, we found that one of the earliest expressed arterial genes, Delta like 4 (Dll4), is significantly reduced in the yolk sac of FoxO1 mutants without being substantially affected in the embryo proper. We show that in the yolk sac, FOXO1 not only binds directly to a subset of previously identified Sprouty2 gene regulatory elements (GREs), as well as newly identified, evolutionarily conserved Sprouty4 GREs, but can also repress their expression. Additionally, over expression of Sprouty4 in transient transgenic embryos largely recapitulates reduced expression of arterial genes seen in endothelial FoxO1 mutant mouse embryos. Together, these data reveal a novel role for FOXO1 as a key early transcriptional repressor controlling both pre-flow arterial specification and subsequent vessel remodeling within the murine yolk sac.

developmental biology↗

bioRxiv2021

Whole genome analysis for 163 guide RNAs in Cas9 edited mice reveals minimal off-target activity

Introductory ParagraphThe Knockout Mouse Phenotyping Program (KOMP2) uses CRISRPR/Cas9 for high-throughput mouse line production to generate null alleles in the inbred C57BL/6N strain for broad-based in vivo phenotyping. In order to assess the risk of spurious S. pyogenes Cas9-induced off-target mutagenesis, we applied whole genome sequencing to compare the genomes of 50 Cas9-derived founder mice representing 163 different gRNAs to 28 untreated inbred control mice. Our analysis pipeline detected 28 off-target sequence variants associated with 21 guides. These potential off-targets were identified in 18/50 (36%) founders with 9/28 (32%) independently validated corresponding to 8 founder animals. In total, only 4.9% (8/163) of all guides exhibited off-target activity resulting in a rate of 0.16 Cas9 off-target mutations per founder analyzed. In comparison, we observed ~1225 unique variants in each mouse regardless of whether or not it was exposed to Cas9. These findings indicate that Cas9-mediated off-target mutagenesis is rare in founder knockout mice generated using guide RNAs designed to minimize off-target risk. Overall, bona fide off-target variants comprise a small fraction of the genetic heterogeneity found in carefully maintained colonies of inbred strains.

genetics↗

bioRxiv2019

CreLite: An Optogenetically Controlled Cre/loxP System Using Red Light

Precise manipulation of gene expression with temporal and spatial control is essential for functional studies and the determination of cell lineage relationships in complex biological systems. The Cre-loxP system is commonly used for gene manipulation at desired times and places. However, specificity is dependent on the availability of tissue- or cell-specific regulatory elements used in combination with Cre or CreER (tamoxifen-inducible). Here we present CreLite, an optogenetically-controlled Cre system using red light in developing zebrafish embryos. Cre activity is disabled by splitting Cre and fusing the inactive halves with the Arabidopsis thaliana red light-inducible binding partners, PhyB and PIF6. In addition, PhyB-PIF6 binding requires phycocyanobilin (PCB), providing an additional layer of control. Upon exposure to red light (660 nm) illumination, the PhyB-CreC and PIF6-CreN fusion proteins come together in the presence of PCB to restore Cre activity. Red-light exposure of transgenic zebrafish embryos harboring a Cre-dependent multi-color fluorescent protein reporter (ubi:zebrabow) injected with CreLite mRNAs and PCB, resulted in Cre activity as measured by the generation of multi-spectral cell labeling in various tissues, including heart, skeletal muscle and epithelium. We show that CreLite can be used for gene manipulations in whole embryos or small groups of cells at different stages of development. CreLite provides a novel optogenetic tool for precise temporal and spatial control of gene expression in zebrafish embryos that may also be useful in cell culture, ex vivo organ culture, and other animal models for developmental biology studies.

molecular biology↗

bioRxiv2019

Human and mouse essentiality screens as a resource for disease gene discovery

Although genomic sequencing has been transformative in the study of rare genetic diseases, identifying causal variants remains a considerable challenge that can be addressed in part by new gene-specific knowledge. Here, we integrate measures of how essential a gene is to supporting life, as inferred from the comprehensive viability and phenotyping screens performed on knockout mice by the International Mouse Phenotyping Consortium and from human cell line essentiality screens. We propose a novel, cross-species gene classification across the Full Spectrum of Intolerance to Loss-of-function (FUSIL) and demonstrate that genes in five mutually exclusive FUSIL categories have differing characteristics in the biological processes they regulate, tissue expression levels and human mutation rates. Most notably, Mendelian disease genes, particularly those associated with developmental disorders, are highly overrepresented in the developmental lethal category, representing genes not essential for cell survival but required for organism development. Exploiting this finding, we have screened developmental disorder cases from three independent disease sequencing consortia and identified potentially pathogenic, de novo variants shared in different patients for several developmental lethal genes that have not previously been associated with rare disease. We therefore propose FUSIL as an efficient resource for disease gene discovery.

genomics↗

bioRxiv2017

Employing single-stranded DNA donors for the high-throughput production of conditional knockout alleles in mice

The International Mouse Phenotyping Consortium is generating null allele mice for every protein-coding gene in the genome and characterizing these mice to identify gene-phenotype associations. To test the feasibility of using CRISPR/Cas9 gene editing to generate conditional knockout mice for this large-scale resource, we employed Cas9-mediated homology driven repair (HDR) with short and long single-stranded oligodeoxynucleotides (ssODNs and lssODNs). Using pairs of guides and ssODNs donating loxP sites, we obtained putative conditional allele founder mice, harboring both loxP sites, for 23 of 30 genes targeted. LoxP sites integrated in cis in at least one F0 for 18 of 23 targeted genes. However, loxP sites were mutagenized in 4 of 18 in cis lines. HDR efficiency correlated with Cas9 cutting efficiency but was not influenced by ssODN homology arm symmetry. By contrast, using pairs of guides and a single lssODN to introduce a loxP-flanked exon, conditional allele founders were generated for all 4 genes targeted. Our studies demonstrate that Cas9-mediated HDR with pairs of ssODNs can generate conditional null alleles at many loci, but reveal inefficiencies when applied at scale. In contrast, lssODNs are amenable to high-throughput production of conditional alleles when they can be employed.

genetics↗