PaperPlayer biorxiv genetics

Link to bioRxiv paper:

http://biorxiv.org/cgi/content/short/2020.08.04.236968v1?rss=1

Authors: Plasil, S. L., Seth, A., Homanics, G. E.

Abstract:

The development of CRISPR/Cas9 technology has vastly sped up the process of genome editing by introducing a bacterial system that can be exploited for reverse genetics-based research. However, generating homozygous knockout (KO) animals using traditional CRISPR/Cas9-mediated techniques requires three generations of animals. A founder animal with a desired mutation is crossed to produce heterozygous F1 offspring which are subsequently interbred to generate homozygous F2 KO animals. This study describes a novel adaptation of the CRISPR/Cas9-mediated method to develop a homozygous gene-targeted KO animal cohort in one generation. A well-characterized ethanol-responsive gene, MyD88, was chosen as a candidate gene for generation of MyD88-/- mice as proof of concept. Previous studies have reported changes in ethanol-related behavioral outcomes in MyD88 KO mice. Therefore, it was hypothesized that a successful one-generation KO of MyD88 should reproduce decreased responses to ethanols sedative effects, as well as increased ethanol consumption in males that were observed in previous studies. One-cell mouse embryos were simultaneously electroporated with four gRNAs targeting a critical Exon of MyD88 along with Cas9. DNA and RNA analysis of founder mice revealed a complex mix of genetic alterations, all of which were predicted to ablate MyD88 gene function. This study additionally compared responses of Mock treatment control mice generated through electroporation to controls purchased from a vendor. No substantial behavioral changes were noted between control cohorts. Overall, the CRISPR/Cas9 KO protocol reported here, which we call CRISPR Turbo Accelerated KnockOut (CRISPy TAKO), will be useful for reverse genetic in vivo screens of gene function in whole animals.

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Link to bioRxiv paper:

http://biorxiv.org/cgi/content/short/2020.08.05.236901v1?rss=1

Authors: Lin, Z., Seal, S., Basu, S.

Abstract:

SNP heritability of a trait is measured by the proportion of total variance explained by the additive effects of genome-wide single nucleotide polymorphisms (SNPs). Linear mixed models are routinely used to estimate SNP heritability for many complex traits. The basic concept behind this approach is to model genetic contribution as a random effect, where the variance of this genetic contribution attributes to the heritability of the trait. This linear mixed model approach requires estimation of relatedness among individuals in the sample, which is usually captured by estimating a genetic relationship matrix (GRM). Heritability is estimated by the restricted maximum likelihood (REML) or method of moments (MOM) approaches, and this estimation relies heavily on the GRM computed from the genetic data on individuals. Presence of population substructure in the data could significantly impact the GRM estimation and may introduce bias in heritability estimation. The common practice of accounting for such population substructure is to adjust for the top few principal components of the GRM as covariates in the linear mixed model. Here we propose an alternative way of estimating heritability in multi-ethnic studies. Our proposed approach is a MOM estimator derived from the Haseman-Elston regression and gives an asymptotically unbiased estimate of heritability in presence of population stratification. It introduces adjustments for the population stratification in a second-order estimating equation and allows for the total phenotypic variance vary by ethnicity. We study the performance of different MOM and REML approaches in presence of population stratification through extensive simulation studies. We estimate the heritability of height, weight and other anthropometric traits in the UK Biobank cohort to investigate the impact of subtle population substructure on SNP heritability estimation.

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Link to bioRxiv paper:

http://biorxiv.org/cgi/content/short/2020.08.05.237768v1?rss=1

Authors: Pachano, T., Sanchez-Gaya, V., Mariner-Fauli, M., Ealo, T., Asenjo, H. G., Respuela, P., Cruz-Molina, S., van IJcken, W., Landeira, D., Rada-Iglesias, A.

Abstract:

CpG islands (CGIs) represent a distinctive and widespread genetic feature of vertebrate genomes, being associated with ~70% of all annotated gene promoters. CGIs have been proposed to control transcription initiation by conferring nearby promoters with unique chromatin properties. In addition, there are thousands of distal or orphan CGIs (oCGIs) whose functional relevance and mechanism of action are barely known. Here we show that oCGIs are an essential component of poised enhancers (PEs) that boost their long-range regulatory activity and dictate the responsiveness of their target genes. Using a CRISPR/Cas9 knock-in strategy in mESC, we introduced PEs with or without oCGIs within topological associating domains (TADs) harbouring genes with different types of promoters. By evaluating the chromatin, topological and regulatory properties of the engineered PEs, we uncover that, rather than increasing their local activation, oCGIs boost the physical and functional communication between PEs and distally located developmental genes. Furthermore, we demonstrate that developmental genes with CpG rich promoters are particularly responsive to PEs and that such responsiveness depends on the presence of oCGIs. Therefore, our work unveils a novel role for CGIs as genetic determinants of the compatibility between genes and enhancers, thus providing major insights into how developmental gene expression programs are deployed under both physiological and pathological conditions.

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Link to bioRxiv paper:

http://biorxiv.org/cgi/content/short/2020.08.05.237172v1?rss=1

Authors: Paschini, M., Reyes, C. M., Gillespie, A. E., Lewis, K. A., Glustrom, L. W., Sharpee, T. O., Wuttke, D. S., Lundblad, V.

Abstract:

Telomeres present unique challenges for genomes with linear chromosomes, including the inability of the semi-conservative DNA replication machinery to fully duplicate the ends of linear molecules. This is solved in virtually all eukaryotes by the enzyme telomerase, through the addition of telomeric repeats onto chromosome ends. It is widely assumed that the primary site of action for telomerase is the single-stranded G-rich overhang at the ends of chromosomes, formed after DNA replication is complete. We show here that the preferred substrate for telomerase in wild type yeast is instead a collapsed fork generated during replication of duplex telomeric DNA. Furthermore, newly collapsed forks are extensively elongated by telomerase by as much as ~200 nucleotides in a single cell division, indicating that a major source of newly synthesized telomeric repeats in wild type cells occurs at collapsed forks. Fork collapse and the subsequent response by telomerase are coordinated by the dual activities of a telomere-dedicated RPA-like complex, which facilitates replication of duplex telomeric DNA and also recruits telomerase to the fork, thereby ensuring a high probability of re-elongation if DNA replication fails. We further show that the ability of telomerase to elongate newly collapsed forks is dependent on the Rad51 protein, indicating that telomerase activity in response to fork collapse proceeds through a regulatory pathway distinct from how telomerase engages fully replicated chromosome termini. We propose a new model in which spontaneous replication fork collapse and the subsequent response by telomerase is a major determinant of telomere length homeostasis.

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Link to bioRxiv paper:

http://biorxiv.org/cgi/content/short/2020.08.05.232348v1?rss=1

Authors: Bosch, J. A., Birchak, G., Perrimon, N.

Abstract:

Precise genome editing is a valuable tool to study gene function in model organisms. Prime editing, a precise editing system developed in mammalian cells, does not require double strand breaks or donor DNA and has low off-target effects. Here, we applied prime editing for the model organism Drosophila melanogaster and developed conditions for optimal editing. By expressing prime editing components in cultured cells or somatic cells of transgenic flies, we precisely installed premature stop codons in three classical visible marker genes, ebony, white, and forked. Furthermore, by restricting editing to germ cells, we demonstrate efficient germ line transmission of a precise edit in ebony to ~50% of flies. Our results suggest that prime editing is a useful system in Drosophila to study gene function, such as engineering precise point mutations, deletions, or epitope tags.

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Link to bioRxiv paper:

http://biorxiv.org/cgi/content/short/2020.08.05.216739v1?rss=1

Authors: Kosicki, M., Allen, F., Bradley, A.

Abstract:

Repair of Cas9-induced double-stranded breaks results primarily in formation of small indels, but can also cause potentially harmful large deletions. While mechanisms leading to the creation of small indels are relatively well understood, very little is known about the origins of large deletions. Using a novel library of clonal mouse embryonic stem cells bona fide deficient for 32 DNA repair genes, we have shown that large deletion frequency increases in cells impaired for non-homologous end joining and decreases in cells deficient for the central resection gene Nbn and the microhomology-mediated end joining gene Polq. Across deficient clones, increase in large deletion frequency was closely correlated with the increase in the extent of microhomology and the size of small indels, implying a continuity of repair processes across different genomic scales. Furthermore, by targeting diverse genomic sites, we identified examples of repair processes that were highly locus-specific, discovering a novel role for exonuclease Trex1. Finally, we present evidence that indel sizes increase with the overall efficiency of Cas9 mutagenesis. These findings may have impact on both basic research and clinical use of CRISPR-Cas9, in particular in conjunction with repair pathway modulation.

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Link to bioRxiv paper:

http://biorxiv.org/cgi/content/short/2020.08.03.235127v1?rss=1

Authors: Haskell, D., Zinovyeva, A.

Abstract:

microRNAs (miRNAs) and RNA binding proteins (RBPs) regulate gene expression at the post-transcriptional level, but the extent to which these key regulators of gene expression coordinate and the precise mechanisms of their coordination are not well understood. RNA binding proteins often have recognizable RNA binding domains that correlate with specific protein function. Recently, several RBPs containing K Homology (KH) RNA binding domains were shown to work with miRNAs to regulate gene expression, raising the possibility that KH domains may be important for coordinating with miRNA pathways in gene expression regulation. To ascertain whether additional KH domain proteins functionally interact with miRNAs during Caenorhabditis elegans development, we knocked down twenty-four genes encoding KH-domain proteins in several miRNA sensitized genetic backgrounds. Here, we report that a majority of the KH domain-containing genes genetically interact with multiple miRNAs and Argonaute alg-1. Interestingly, two KH domain genes, predicted splicing factors sfa- and asd-2, genetically interacted with all of the miRNA mutants tested, while other KH domain genes exhibited functional interactions only with specific miRNAs. Our domain architecture and phylogenetic relationship analyses of the C. elegans KH domain-containing proteins revealed potential groups that may share both structure and function. Collectively, we show that many C. elegans KH domain RBPs functionally interact with miRNAs, suggesting direct or indirect coordination between these two classes of post-transcriptional gene expression regulators.

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Link to bioRxiv paper:

http://biorxiv.org/cgi/content/short/2020.08.04.235994v1?rss=1

Authors: Strausz, S., Ruotsalainen, S. E., Ollila, H. M., Karjalainen, J., Reeve, M., Kurki, M., Mars, N., Havulinna, A. S., Kiiskinen, T., Mansour Aly, D., Ahlqvist, E., Teder-Laving, M., Palta, P., Groop, L., Magi, R., Makitie, A., Salomaa, V., Bachour, A., Tuomi, T., Palotie, A., Palotie, T., Ripatti, S.

Abstract:

There is currently only limited understanding of the genetic aetiology of obstructive sleep apnoea (OSA). The aim of our study is to identify genetic loci associated with OSA risk and to test if OSA and its comorbidities share a common genetic background. We conducted the first large-scale genome-wide association study of OSA using FinnGen Study (217,955 individuals) with 16,761 OSA patients identified using nationwide health registries. We estimated 8.3% [0.06-0.11] heritability and identified five loci associated with OSA (P < 5.0x10^-8): rs4837016 near GTPase activating protein and VPS9 domains 1 (GAPVD1), rs10928560 near C-X-C motif chemokine receptor 4 (CXCR4), rs185932673 near Calcium/calmodulin-dependent protein kinase ID (CAMK1D) and rs9937053 near Fat mass and obesity-associated protein (FTO) - a variant previously associated with body mass index (BMI). In a BMI-adjusted analysis, an association was observed for rs10507084 near Rhabdomyosarcoma 2 associated transcript (RMST)/NEDD1 gamma-tubulin ring complex targeting factor (NEDD1). We found genetic correlations between OSA and BMI (rg=0.72 [0.62-0.83]) and with comorbidities including hypertension, type 2 diabetes (T2D), coronary heart disease (CHD), stroke, depression, hypothyroidism, asthma and inflammatory rheumatic diseases (IRD) (rg > 0.30). Polygenic risk score (PRS) for BMI showed 1.98-fold increased OSA risk between the highest and the lowest quintile and Mendelian randomization supported a causal relationship between BMI and OSA. Our findings support the causal link between obesity and OSA and joint genetic basis between OSA and comorbidities.

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Link to bioRxiv paper:

http://biorxiv.org/cgi/content/short/2020.07.31.231514v1?rss=1

Authors: Shastry, V., Adams, P. E., Lindtke, D., Mandeville, E. G., Parchman, T. L., Gompert, Z., Buerkle, C. A.

Abstract:

Non-random mating among individuals can lead to spatial clustering of genetically similar individuals and population stratification. This deviation from panmixia is commonly observed in natural populations. Consequently, individuals can have parentage in single populations or involving hybridization between differentiated populations. Accounting for this mixture and structure is important when mapping the genetics of traits and learning about the formative evolutionary processes that shape genetic variation among individuals and populations. Stratified genetic relatedness among individuals is commonly quantified using estimates of ancestry that are derived from a statistical model. Development of these models for polyploid and mixed-ploidy individuals and populations has lagged behind those for diploids. Here, we extend and test a hierarchical Bayesian model, called entropy, which can utilize low-depth sequence data to estimate genotype and ancestry parameters in autopolyploid and mixed-ploidy individuals (including sex chromosomes and autosomes within individuals). Our analysis of simulated data illustrated the trade-off between sequencing depth and genome coverage and found lower error associated with low depth sequencing across a larger fraction of the genome than with high depth sequencing across a smaller fraction of the genome. The model has high accuracy and sensitivity as verified with simulated data and through analysis of admixture among populations of diploid and tetraploid Arabidopsis arenosa.

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Link to bioRxiv paper:

http://biorxiv.org/cgi/content/short/2020.07.31.231126v1?rss=1

Authors: McCartney, D. L., Chasman, D. I., Visscher, P. M., Muniz-Terrera, G., Cox, S. R., Russ, T. C., Marioni, R. E., Mur, J.

Abstract:

Genetic variation in VKORC1 is associated with differences in the coagulation of blood and consequentially with sensitivity to the drug warfarin. Variation in VKORC1 has also been linked to parental dementia. However, it is unclear whether the relationship persists for the diagnosis in patients themselves, whether the association holds only for certain forms of dementia, and if those taking warfarin are at greater risk. Here, we use data from 211,423 participants from UK Biobank to examine the relationship between VKORC1, risk of dementia, and the interplay with warfarin use. We find that the T-allele in rs9923231 confers a greater risk for vascular dementia (OR=1.28, p=0.0069), but not for general dementia (OR=1.04, p=0.21) or Alzheimer dementia (OR=1.05, p=0.35), and that the risk of vascular dementia is not affected by warfarin use in carriers of the T-allele. Our study reports for the first time an association between rs9923231 and vascular dementia, but further research is warranted to explore potential mechanisms and specify the relationship between rs9923231 and features of vascular dementia.

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