Biology subjects

Dethlefsen, O.

Publications and source records attributed to Dethlefsen, O..

4 recordsLinked to original sources

bioRxiv2019

Pax6 and KDM5C co-occupy a subset of developmentally critical genes including Notch signaling regulators in neural progenitors

Pax6 is a key transcription factor in neural development. While generally viewed as a transcriptional activator, mechanisms underlying Pax6 function as a repressor is less well understood. Here we show that Pax6 acts as a direct repressor of transcription associated with a decrease in H3K4me3 levels. Genome wide analysis of the co-occupancy of the H3K4 demethylase KDM5C and Pax6 with H3K4me3-negative regions revealed 177 peaks on 131 genes. Specific analysis of these Pax6/KDM5C/H3K4me3-peaks unveiled a number of genes associated with Notch signaling, including Dll1, Dll4, and Hes1. RNA knockdown of PAX6/KDM5C in human neural progenitors resulted in increased DLL4 gene expression, decreased DLL1 expression, and no significant effect on HES1 mRNA levels, differences that could be due to gene-specific variations in the chromatin landscape. Our findings suggest that PAX6 and KDM5C co-regulate a subset of genes implicated in brain development, including members of the Notch signaling family.

molecular biology↗

bioRxiv2019

Lithium treatment reverses irradiation-induced changes in rodent neural progenitors

Cranial radiotherapy in children has detrimental effects on cognition, mood, and social competence in young cancer survivors. Treatments harnessing hippocampal neurogenesis are currently of great relevance in this context, and we previously showed that voluntary running introduced long after irradiation rescued hippocampal neurogenesis in young mice (Naylor et al. 2008a). Lithium, a well-known mood stabilizer, has both neuroprotective, pro-neurogenic as well as anti-tumor effects, and in the current study we introduced lithium treatment 4 weeks after irradiation, analogous to the voluntary running study. Female mice received a single 4 Gy whole-brain irradiation dose at postnatal day (PND) 21 and were randomized to 0.24% Li2CO3 chow or normal chow from PND 49 to 77. Hippocampal neurogenesis was assessed at PND 77, 91 and 105. We found that lithium treatment had a pro-proliferative effect on neural progenitors and promoted neuronal integration upon its discontinuation. Gene expression profiling and DNA methylation analysis identified two novel factors related to the observed effects, Tppp, associated with proliferation, and GAD2/65, associated with neuronal signaling. Our results show that lithium treatment reverses irradiation-induced impairment of hippocampal neurogenesis even when introduced long after the injury. We propose that lithium treatment should be intermittent in order to first make neural progenitors proliferate and then, upon discontinuation, allow them to differentiate. Our findings suggest that pharmacological treatment of cognitive so-called late effects in childhood cancer survivors is possible.

neuroscience↗

bioRxiv2018

Zebrafish larvae as a model system for systematic characterization of drugs and genes in dyslipidemia and atherosclerosis

BackgroundHundreds of loci have been robustly associated with circulating lipids, atherosclerosis and coronary artery disease; but for most loci the causal genes and mechanisms remain uncharacterized.\n\nMethodsWe developed a semi-automated experimental pipeline for systematic, quantitative, large-scale characterization of mechanisms, drugs and genes associated with dyslipidemia and atherosclerosis in a zebrafish model system. We validated our pipeline using a dietary (n>2000), drug treatment (n>1000), and genetic intervention (n=384), and used it to characterize three candidate genes in a GWAS-identified pleiotropic locus on chr 19p13.11 (n>500).\n\nResultsOur results show that five days of overfeeding and cholesterol supplementation had independent pro-atherogenic effects, which could be diminished by concomitant treatment with atorvastatin and ezetimibe. CRISPR-Cas9-induced mutations in orthologues of proof-of-concept genes resulted in higher LDL cholesterol levels (apoea), and more early stage atherosclerosis (apobb.1). Finally, our pipeline helped identify putative causal genes for circulating lipids and early-stage atherosclerosis (LPAR2 and GATAD2A).\n\nConclusionsIn summary, our pipeline facilitates systematic, in vivo characterization of drugs and candidate genes to increase our understanding of disease etiology, and can likely help identify novel targets for therapeutic intervention.

genomics↗

bioRxiv2018

Translating GWAS-identified loci for cardiac rhythm and rate using an in vivo, image-based, large-scale genetic screen in zebrafish

A meta-analysis of genome-wide association studies (GWAS) identified eight loci that are associated with heart rate variability (HRV), but candidate genes in these loci remain uncharacterized. We developed an image- and CRISPR/Cas9-based pipeline to systematically characterize candidate genes for HRV in live zebrafish embryos. Nine zebrafish orthologues of six human candidate genes were targeted simultaneously in eggs from fish that transgenically express GFP on smooth muscle cells (Tg[acta2:GFP]), to visualize the beating heart. An automated analysis of repeated 30s recordings of beating atria in 381 live, intact zebrafish embryos at 2 and 5 days post-fertilization highlighted genes that influence HRV (hcn4 and si:dkey-65j6.2 [KIAA1755]); heart rate (rgs6 and hcn4); and the risk of sinoatrial pauses and arrests (hcn4). Exposure to 10 or 25{micro}M ivabradine - an open channel blocker of HCNs - for 24h resulted in a dose-dependent higher HRV and lower heart rate at 5 days post-fertilization. Hence, our screen confirmed the role of established genes for heart rate and rhythm (RGS6 and HCN4); showed that ivabradine reduces heart rate and increases HRV in zebrafish embryos, as it does in humans; and highlighted a novel gene that plays a role in HRV (KIAA1755).

genomics↗