Modelling genetic networks involved in the activity-dependent modulation of adult neurogenesis

Die Bildung neuen Nervenzellen im erwachsenen Gehirn—adulte Neurogenese—ist bei Säugetieren auf spezifische Regionen beschränkt. Eine der beiden bekannten ist der Hippokampus, eine Gehirnstruktur, die eine wichtige Rolle beim Lernen sowie der Gedächtnisbildung spielt. Ein Reservoir von neuralen Stammzellen befindet sich in der subgranulären Zone des hippokampalen Gyrus dentatus. Diese Zellen teilen sich fortwährend und bilden neue Nervenzellen. Die Regulation adulter hippokampaler Neurogenese wird sowohl von der Umgebung beeinflusst als auch von mehreren Genen gesteuert. In der vorliegenden Arbeit wurden mittels Hochdurchsatz- Genexpressionsverfahren die an der Neurogenese beteiligten Gene identifiziert und ihr Zusammenspiel untersucht. Anhand von genetischen, umgebungsbedingten und zeitlichen Angaben und Variationen wurde ein vielseitiger Datensatz erstellt, der einen multidimensionalen Blick auf den proliferativen Phänotyp verschafft. Netzwerke aus Gen-Gen und Gen-Phänotyp Interaktionen wurden beschrieben und in einer mehrschichtigen Ressource zusammengefasst. Ein Kern-Netzwerk bestehend aus immerwiederkehrenden Modulen aus verschiedenen Ebenen wurde anhand von Proliferation als Keim-Phänotyp identifiziert. Aus diesem Kern-Netzwerk sind neue Gene und ihre Interaktionen hervorgegangen, die potentiell bei der Regulierung adulter Neurogenesis beteiligt sind.:Zusammenfassung i Abstract iii Acknowledgements vii Contents ix Preface xiii General Introduction 1 Adult Neurogenesis 1 Historical setting 1 Neurogenesis exists in two regions of the adult mammalian brain 1 Implications of neurogenesis in the hippocampus 1 The Hippocampal Formation 2 Function of the hippocampus in learning and memory 2 The functional role of adult neurogenesis 2 Anatomy of the hippocampal formation 2 Neural Precursor Biology 3 The subgranular zone as a neurogenic niche 3 Neuronal maturation is a multi-step pathway 3 Regulation of Adult Neurogenesis 3 Neurogenesis is modulated by age 3 Neurogenesis is modulated by environmental factors 4 Neurogenesis is modulated by genetic background 4 Genetics of the BXD RI Cross 5 C57BL/6 and DBA/2 5 Recombinant Inbred Lines 5 The BXD panel 6 Quantitative genetics 6 Microarray Analysis 7 The concept of ‘whole genome’ expression analysis 7 Technical considerations 8 Theoretical considerations 9 Current Analytical Methods 9 Network Analysis 10 Network Description and Terminology 10 Graph Theory 10 Multiple-Network Comparison 11 Biological networks 11 Types of Biological Network 11 Sources of Network Data 12 Biological Significance of Networks 12 Aim of the current work 13 Methods and Materials 15 Animals 15 BXD panel 15 Progenitor strains 15 Animal behaviour 15 Running wheel activity 15 Enriched environment 16 Morris water maze 16 Open field test 16 Corticosterone assay 16 Histology 17 Tissue collection 17 BrdU staining 17 Statistics 17 Cell culture 18 Maintenance and differentiation 18 Immunostaining 18 RNA isolation 18 Microarray processing 18 Affymetrix arrays 18 M430v2 probe reannotation 19 Illumina arrays 19 Illumina probe reannotation 19 Bioinformatics 19 Translating the STRING network 19 QTL mapping 20 Network graph layout 20 Triplot 20 Enrichment analysis 20 Mammalian Adult Neurogenesis Gene Ontology 21 Introduction 21 Results 25 The cell stage ontology 25 The process ontology 25 Genes known to regulate hippocampal adult neurogenesis 26 Enrichment analysis 27 The MANGO gene network 27 Discussion 28 Hippocampal Coexpression Networks from the BXD Panel 31 Introduction 31 Results 32 Variation and covariation of gene expression across a panel of inbred lines 32 A hippocampal expression correlation network 32 Diverse neurogenesis phenotypes associate with discrete transcript networks 34 Discussion 34 Interactions Between Gene Expression Phenotypes and Genotype 37 Introduction 37 Results 39 QTL analysis and interval definitions 39 Pleiotropic loci and ‘trans-bands’ 39 Transcript expression proxy-QTLs can help in dissection of complex phenotypes 41 Interaction network 43 Discussion 43 Strain-Dependent Effects of Environment 47 Introduction 47 Results 48 Effects of strain and environment on precursor cell proliferation 48 Effects of strain and environment on learning behaviour 52 Transcript expression associated with different housing environments 53 Strain differences in transcript regulation 55 Distance-weighted coexpression networks 57 Discussion 58 Expression Time Course from Differentiating Cell Culture 61 Introduction 61 Results 63 Differentiation of proliferating precursors into neurons in vitro 63 Transcripts associated with stages of differentiation 63 Early events in NPC differentiation 64 A network of transcript coexpression during in vitro differentiation 66 Discussion 67 Integrated Gene Interaction Networks 71 Introduction 71 Results 72 Description of network layers 72 Merging of network layers to a multigraph 74 A network of genes controls neural precursor proliferation in the adult hippocampus 75 Novel candidate regulators of adult hippocampal neurogenesis 77 Novel pathways regulating adult hippocampal neurogenesis 77 Discussion 79 General Discussion 81 References 89 Selbständigkeitserklärung 107Neurogenesis, the production of new neurons, is restricted in the adult brain of mammals to only a few regions. One of these sites of adult neurogenesis is the hippocampus, a structure essential for many types of learning. A pool of stem cells is maintained in the subgranular zone of the hippocampal dentate gyrus which proliferate and can differentiate into new neurons, astrocytes and oligodendroctytes. Regulation of adult hippocampal neurogenesis occurs in response to en- vironmental stimuli and is under the control of many genes. This work employs high-throughput gene expression technologies to identify these genes and their interactions with each other and the neurogenesis phenotype. Harnessing variation from genetic, environmental and temporal sources, a multi-faceted dataset has been generated which offers a multidimensional view of the neural precursor proliferation phenotype. Networks of gene-gene and gene-phenotype interac- tions have been described and merged into a multilayer resource. A core subnetwork derived from modules recurring in the different layers has been identified using the proliferation phenotype as a seed. This subnetwork has suggested novel genes and interactions potentially involved in the regulation of adult hippocampal neurogenesis.:Zusammenfassung i Abstract iii Acknowledgements vii Contents ix Preface xiii General Introduction 1 Adult Neurogenesis 1 Historical setting 1 Neurogenesis exists in two regions of the adult mammalian brain 1 Implications of neurogenesis in the hippocampus 1 The Hippocampal Formation 2 Function of the hippocampus in learning and memory 2 The functional role of adult neurogenesis 2 Anatomy of the hippocampal formation 2 Neural Precursor Biology 3 The subgranular zone as a neurogenic niche 3 Neuronal maturation is a multi-step pathway 3 Regulation of Adult Neurogenesis 3 Neurogenesis is modulated by age 3 Neurogenesis is modulated by environmental factors 4 Neurogenesis is modulated by genetic background 4 Genetics of the BXD RI Cross 5 C57BL/6 and DBA/2 5 Recombinant Inbred Lines 5 The BXD panel 6 Quantitative genetics 6 Microarray Analysis 7 The concept of ‘whole genome’ expression analysis 7 Technical considerations 8 Theoretical considerations 9 Current Analytical Methods 9 Network Analysis 10 Network Description and Terminology 10 Graph Theory 10 Multiple-Network Comparison 11 Biological networks 11 Types of Biological Network 11 Sources of Network Data 12 Biological Significance of Networks 12 Aim of the current work 13 Methods and Materials 15 Animals 15 BXD panel 15 Progenitor strains 15 Animal behaviour 15 Running wheel activity 15 Enriched environment 16 Morris water maze 16 Open field test 16 Corticosterone assay 16 Histology 17 Tissue collection 17 BrdU staining 17 Statistics 17 Cell culture 18 Maintenance and differentiation 18 Immunostaining 18 RNA isolation 18 Microarray processing 18 Affymetrix arrays 18 M430v2 probe reannotation 19 Illumina arrays 19 Illumina probe reannotation 19 Bioinformatics 19 Translating the STRING network 19 QTL mapping 20 Network graph layout 20 Triplot 20 Enrichment analysis 20 Mammalian Adult Neurogenesis Gene Ontology 21 Introduction 21 Results 25 The cell stage ontology 25 The process ontology 25 Genes known to regulate hippocampal adult neurogenesis 26 Enrichment analysis 27 The MANGO gene network 27 Discussion 28 Hippocampal Coexpression Networks from the BXD Panel 31 Introduction 31 Results 32 Variation and covariation of gene expression across a panel of inbred lines 32 A hippocampal expression correlation network 32 Diverse neurogenesis phenotypes associate with discrete transcript networks 34 Discussion 34 Interactions Between Gene Expression Phenotypes and Genotype 37 Introduction 37 Results 39 QTL analysis and interval definitions 39 Pleiotropic loci and ‘trans-bands’ 39 Transcript expression proxy-QTLs can help in dissection of complex phenotypes 41 Interaction network 43 Discussion 43 Strain-Dependent Effects of Environment 47 Introduction 47 Results 48 Effects of strain and environment on precursor cell proliferation 48 Effects of strain and environment on learning behaviour 52 Transcript expression associated with different housing environments 53 Strain differences in transcript regulation 55 Distance-weighted coexpression networks 57 Discussion 58 Expression Time Course from Differentiating Cell Culture 61 Introduction 61 Results 63 Differentiation of proliferating precursors into neurons in vitro 63 Transcripts associated with stages of differentiation 63 Early events in NPC differentiation 64 A network of transcript coexpression during in vitro differentiation 66 Discussion 67 Integrated Gene Interaction Networks 71 Introduction 71 Results 72 Description of network layers 72 Merging of network layers to a multigraph 74 A network of genes controls neural precursor proliferation in the adult hippocampus 75 Novel candidate regulators of adult hippocampal neurogenesis 77 Novel pathways regulating adult hippocampal neurogenesis 77 Discussion 79 General Discussion 81 References 89 Selbständigkeitserklärung 10

Prolactin stimulates precursor cells in the adult mouse hippocampus

In the search for ways to combat degenerative neurological disorders, neurogenesis-stimulating factors are proving to be a promising area of research. In this study, we show that the hormonal factor prolactin (PRL) can activate a pool of latent precursor cells in the adult mouse hippocampus. Using an in vitro neurosphere assay, we found that the addition of exogenous PRL to primary adult hippocampal cells resulted in an approximate 50% increase in neurosphere number. In addition, direct infusion of PRL into the adult dentate gyrus also resulted in a significant increase in neurosphere number. Together these data indicate that exogenous PRL can increase hippocampal precursor numbers both in vitro and in vivo. Conversely, PRL null mice showed a significant reduction (approximately 80%) in the number of hippocampal-derived neurospheres. Interestingly, no deficit in precursor proliferation was observed in vivo, indicating that in this situation other niche factors can compensate for a loss in PRL. The PRL loss resulted in learning and memory deficits in the PRL null mice, as indicated by significant deficits in the standard behavioral tests requiring input from the hippocampus. This behavioral deficit was rescued by direct infusion of recombinant PRL into the hippocampus, indicating that a lack of PRL in the adult mouse hippocampus can be correlated with impaired learning and memory

Retinal Organoids from Pluripotent Stem Cells Efficiently Recapitulate Retinogenesis.

The plasticity of pluripotent stem cells provides new possibilities for studying development, degeneration, and regeneration. Protocols for the differentiation of retinal organoids from embryonic stem cells have been developed, which either recapitulate complete eyecup morphogenesis or maximize photoreceptor genesis. Here, we have developed a protocol for the efficient generation of large, 3D-stratified retinal organoids that does not require evagination of optic-vesicle-like structures, which so far limited the organoid yield. Analysis of gene expression in individual organoids, cell birthdating, and interorganoid variation indicate efficient, reproducible, and temporally regulated retinogenesis. Comparative analysis of a transgenic reporter for PAX6, a master regulator of retinogenesis, shows expression in similar cell types in mouse in vivo, and in mouse and human retinal organoids. Early or late Notch signaling inhibition forces cell differentiation, generating organoids enriched with cone or rod photoreceptors, respectively, demonstrating the power of our improved organoid system for future research in stem cell biology and regenerative medicine

Adult Hippocampal Neurogenesis and Plasticity in the Infrapyramidal Bundle of the Mossy Fiber Projection: I. Co-Regulation by Activity

Besides the massive plasticity at the level of synapses, we find in the hippocampus of adult mice and rats two systems with very strong macroscopic structural plasticity: adult neurogenesis, that is the lifelong generation of new granule cells, and dynamic changes in the mossy fibers linking the dentate gyrus to area CA3. In particular the anatomy of the infrapyramidal mossy fiber tract (IMF) changes in response to a variety of extrinsic and intrinsic stimuli. Because mossy fibers are the axons of granule cells, the question arises whether these two types of plasticity are linked. Using immunohistochemistry for markers associated with axonal growth and pro-opiomelanocortin (POMC)–GFP mice to visualize the post-mitotic maturation phase of adult hippocampal neurogenesis, we found that newly generated mossy fibers preferentially but not exclusively contribute to the IMF. The neurogenic stimulus of an enriched environment increased the volume of the IMF. In addition, the IMF grew with a time course consistent with axonal outgrowth from the newborn neurons after the induction of neurogenic seizures using kainate. These results indicate that two aspects of plasticity in the adult hippocampus, mossy fiber size and neurogenesis, are related and may share underlying mechanisms. In a second part of this study, published separately (Krebs et al., 2011) we have addressed the question of whether there is a shared genetics underlying both traits

Genetics of the Hippocampal Transcriptome in Mouse: A Systematic Survey and Online Neurogenomics Resource

Differences in gene expression in the CNS influence behavior and disease susceptibility. To systematically explore the role of normal variation in expression on hippocampal structure and function, we generated an online microarray database for a diverse panel of strains of mice, including most common inbred strains and numerous recombinant inbred lines (www.genenetwork.org). Using this resource, coexpression networks for families of genes can be generated rapidly to test causal models related to function. The data set is optimized for quantitative trait locus (QTL) mapping and was used to identify over 5500 QTLs that modulate mRNA levels. We describe a wide variety of analyses and novel synthetic approaches that take advantage of this resource, and demonstrate how both the data and associated tools can be applied to the study of gene regulation in the hippocampus and relations to structure and function

Cdk5 Regulates Accurate Maturation of Newborn Granule Cells in the Adult Hippocampus

Newborn granule cells become functionally integrated into the synaptic circuitry of the adult dentate gyrus after a morphological and electrophysiological maturation process. The molecular mechanisms by which immature neurons and the neurites extending from them find their appropriate position and target area remain largely unknown. Here we show that single-cell–specific knockdown of cyclin-dependent kinase 5 (cdk5) activity in newborn cells using a retrovirus-based strategy leads to aberrant growth of dendritic processes, which is associated with an altered migration pattern of newborn cells. Even though spine formation and maturation are reduced in cdk5-deficient cells, aberrant dendrites form ectopic synapses onto hilar neurons. These observations identify cdk5 to be critically involved in the maturation and dendrite extension of newborn neurons in the course of adult neurogenesis. The data presented here also suggest a mechanistic dissociation between accurate dendritic targeting and subsequent synapse formation

Integrative Analysis of Low- and High-Resolution eQTL

The study of expression quantitative trait loci (eQTL) is a powerful way of detecting transcriptional regulators at a genomic scale and for elucidating how natural genetic variation impacts gene expression. Power and genetic resolution are heavily affected by the study population: whereas recombinant inbred (RI) strains yield greater statistical power with low genetic resolution, using diverse inbred or outbred strains improves genetic resolution at the cost of lower power. In order to overcome the limitations of both individual approaches, we combine data from RI strains with genetically more diverse strains and analyze hippocampus eQTL data obtained from mouse RI strains (BXD) and from a panel of diverse inbred strains (Mouse Diversity Panel, MDP). We perform a systematic analysis of the consistency of eQTL independently obtained from these two populations and demonstrate that a significant fraction of eQTL can be replicated. Based on existing knowledge from pathway databases we assess different approaches for using the high-resolution MDP data for fine mapping BXD eQTL. Finally, we apply this framework to an eQTL hotspot on chromosome 1 (Qrr1), which has been implicated in a range of neurological traits. Here we present the first systematic examination of the consistency between eQTL obtained independently from the BXD and MDP populations. Our analysis of fine-mapping approaches is based on ‘real life’ data as opposed to simulated data and it allows us to propose a strategy for using MDP data to fine map BXD eQTL. Application of this framework to Qrr1 reveals that this eQTL hotspot is not caused by just one (or few) ‘master regulators’, but actually by a set of polymorphic genes specific to the central nervous system

COVID19 Disease Map, a computational knowledge repository of virus-host interaction mechanisms.

Funder: Bundesministerium für Bildung und ForschungFunder: Bundesministerium für Bildung und Forschung (BMBF)We need to effectively combine the knowledge from surging literature with complex datasets to propose mechanistic models of SARS-CoV-2 infection, improving data interpretation and predicting key targets of intervention. Here, we describe a large-scale community effort to build an open access, interoperable and computable repository of COVID-19 molecular mechanisms. The COVID-19 Disease Map (C19DMap) is a graphical, interactive representation of disease-relevant molecular mechanisms linking many knowledge sources. Notably, it is a computational resource for graph-based analyses and disease modelling. To this end, we established a framework of tools, platforms and guidelines necessary for a multifaceted community of biocurators, domain experts, bioinformaticians and computational biologists. The diagrams of the C19DMap, curated from the literature, are integrated with relevant interaction and text mining databases. We demonstrate the application of network analysis and modelling approaches by concrete examples to highlight new testable hypotheses. This framework helps to find signatures of SARS-CoV-2 predisposition, treatment response or prioritisation of drug candidates. Such an approach may help deal with new waves of COVID-19 or similar pandemics in the long-term perspective