Cell states along oligodendrocyte development and disease

The brain, one of the most complex organs in the body, where an immense diversity of cell states emerges from simple structure, where function arises from sets of regulatory principles and pattern persist where individual cells do not. Revealing the regulatory underpinnings of the brain, from unspecified cell states to diversity, is paramount for achieving a thorough understanding of the development process and generating insight into the disease states of the brain. This thesis is an exploration into how canonical regulatory factors and elements, such as transcription factors and genes, lock a regulatory system in a multi-outcome network with limited possible states. The work in this thesis focuses on the oligodendrocyte lineage, a glial cell known for it’s supportive role in the central nervous system, where it facilitates electrical transmission through the enscheathment of axons. Oligodendrocytes (OLs) lie at the heart of multiple sclerosis (MS), a disease where an immune response is mounted against myelin. As a response, oligodendrocyte precursor cells (OPCs) move towards lesions and remyelinate axons, however, this mechanism fails in later stages of the disease. Thus, an understanding to how OPCs develop is vital to amelioration of the altered oligodendrocyte population. In Paper I we reveal a previously underestimated heterogeneity within the oligodendrocyte lineage in mouse. We show that OL maturation is an ongoing process, albeit, decreasing in frequency with age. Furthermore, complex wheel training in mice revealed that the OLs respond to this challenge through an increase in differentiation. Paper II investigates the cellular response in the experimental autoimmune encephalomyelitis (EAE) disease mouse model of MS, where we find a tailored response by the resident OL population, changed from its normal transcriptional program, expressing a spectrum of genes related to survival, immunological stimulation, phagocytosis, and active differentiation. Furthermore, we provide evidence that OLs can elicit responses from T cells. In Paper III we explore the different waves of OPC generation in the developing mouse brain at embryonic day 13.5 and postnatal day 7. We show that recently Pdgfra expressing cells at the E13.5 time point exhibit a multitude of patterning genes, and we show the emergence of a possible OPC progenitor through the inclusion of a bridging E17.5 time point population. This pre-OPC population is biased towards expressing glial and OL lineage specifying genes such as Olig1, Olig2, Ptprz1, and Bcan. Furthermore, lineage tracing of OPC developmental waves, shows no transcriptional differences, leading us to conclude that OPCs are generally naïve to the time or region of specification. In Paper IV we show that we are able to detect OPC formation in the developing human forebrain. We detect OPCs at the earliest sampled time point post conception week 8. We attempt to recover the path of OPC formation, and investigate the regulatory dynamics in the specification of OPCs

Altered human oligodendrocyte heterogeneity in multiple sclerosis

Oligodendrocyte pathology is increasingly implicated in neurodegenerative diseases as oligodendrocytes both myelinate and provide metabolic support to axons. In multiple sclerosis (MS), demyelination in the central nervous system thus leads to neurodegeneration, but the severity of MS between patients is very variable. Disability does not correlate well with the extent of demyelination1, which suggests that other factors contribute to this variability. One such factor may be oligodendrocyte heterogeneity. Not all oligodendrocytes are the same—those from the mouse spinal cord inherently produce longer myelin sheaths than those from the cortex2, and single-cell analysis of the mouse central nervous system identified further differences3,4. However, the extent of human oligodendrocyte heterogeneity and its possible contribution to MS pathology remain unknown. Here we performed single-nucleus RNA sequencing from white matter areas of post-mortem human brain from patients with MS and from unaffected controls. We identified subclusters of oligodendroglia in control human white matter, some with similarities to mouse, and defined new markers for these cell states. Notably, some subclusters were underrepresented in MS tissue, whereas others were more prevalent. These differences in mature oligodendrocyte subclusters may indicate different functional states of oligodendrocytes in MS lesions. We found similar changes in normal-appearing white matter, showing that MS is a more diffuse disease than its focal demyelination suggests. Our findings of an altered oligodendroglial heterogeneity in MS may be important for understanding disease progression and developing therapeutic approaches

Mapping In Vivo Tumor Oxygenation within Viable Tumor by 19F-MRI and Multispectral Analysis

AbstractQuantifying oxygenation in viable tumor remains a major obstacle toward a better understanding of the tumor microenvironment and improving treatment strategies. Current techniques are often complicated by tumor heterogeneity. Herein, a novel in vivo approach that combines 19F magnetic resonance imaging (19F-MRI)R1 mapping with diffusionbased multispectral (MS) analysis is introduced. This approach restricts the partial pressure of oxygen (pO2) measurements to viable tumor, the tissue of therapeutic interest. The technique exhibited sufficient sensitivity to detect a breathing gas challenge in a xenograft tumor model, and the hypoxic region measured by MS 19F-MRI was strongly correlated with histologic estimates of hypoxia. This approach was then applied to address the effects of antivascular agents on tumor oxygenation, which is a research question that is still under debate. The technique was used to monitor longitudinal pO2 changes in response to an antibody to vascular endothelial growth factor (B20.4.1.1) and a selective dual phosphoinositide 3-kinase/mammalian target of rapamycin inhibitor (GDC-0980). GDC-0980 reduced viable tumor pO2 during a 3-day treatment period, and a significant reduction was also produced by B20.4.1.1. Overall, this method provides an unprecedented view of viable tumor pO2 and contributes to a greater understanding of the effects of antivascular therapies on the tumor's microenvironment

Pest categorisation of Unaspis citri

The Panel on Plant Health performed a pest categorisation of the citrus snow scale, Unaspis citri (Comstock) (Hemiptera: Diaspididae), for the European Union (EU). This is a well-de fi ned and distinguishable species, native to south-eastern Asia, which has spread to many tropical and subtropical regions. U. citri can be a pest of citrus and has been cited on over 28 different species in 16 plant families. In the EU, U. citri occurs in the Azores. There is uncertainty as to whether it occurs in continental Portugal. Reports of it occurring in Greece and Spain are likely to be invalid and based on interception records from these countries. An old Italian record is a misidenti fi cation. U. citri is listed in Annex IIAI of 2000/29/EC as a harmful organism. The international trade of hosts, as either plants for planting, fruit or cut fl owers, provide potential pathways into the EU. However, current EU legislation prohibits the import of citrus plants for planting from third countries. U. citri is mostly con fi ned to coastal humid tropical areas and does not occur in semi-arid areas that are irrigated. Nevertheless, given that it occurs in the Azores and that there are regional climatic similarities between places where U. citri occurs and climates within the EU, and taking EU host distribution into account, U. citri has the potential to establish in the EU, especially in citrus-growing regions around the Mediterranean where losses in quality and yield of citrus could occur. Phytosanitary measures are available to inhibit the likelihood of introduction of U. citri . Considering the criteria within the remit of EFSA to assess the status as a potential Union quarantine pest (QP), or as a potential regulated non-quarantine pest (RNQP), U. citri meets the criteria assessed by EFSA for consideration as a potential Union QP

Pest categorisation of Ips sexdentatus

23The Panelon Plant Health performed a pest categorisation of the six-toothed bark beetle, Ips sexdentatus (Borner) (Coleoptera: Curculionidae, Scolytinae), for the EU. I.sexdentatus is a well-defined and distinguishable species, native to Eurasia and recognised mainly as a pest of pine (Pinus spp., in the pest's whole range) and spruce (mainly Picea orientalis in Turkey and Georgia). It also might occasionally attack Larix spp. and Abies spp. It is distributed throughout the EU (24 Member States). It is a protected zone quarantine pest in Ireland, Cyprus and the United Kingdom (Northern Ireland, Isle of Man), listed in Annex IIB of Council Directive 2000/29/EC. Wood, wood products, bark and wood packaging material are considered as pathways for this pest, which is also able to disperse by flight over tens of kilometres. The adults normally establish on fallen or weakened trees (e.g. after a fire or a drought) and can also mass-attack healthy trees. The males produce aggregation pheromones that attract conspecifics of both sexes. The insects also inoculate pathogenic fungi to their hosts. There are one to five generations per year. The wide current geographical range of I.sexdentatus suggests that it is able to establish anywhere in the EU where its hosts are present. Sanitary thinning or clear-felling are the major control methods. Pheromone mass-trapping is also locally implemented. Quarantine measures are implemented to prevent entry into the protected zones. All criteria for consideration as potential protected zone quarantine pest are met. The criteria for considering I.sexdentatus as a potential regulated non-quarantine pest are not met since plants for planting are not viewed as a pathway.openopenJeger, Michael; Bragard, Claude; Caffier, David; Candresse, Thierry; Chatzivassiliou, Elisavet; Dehnen‐Schmutz, Katharina; Gilioli, Gianni; Jaques Miret, Josep Anton; MacLeod, Alan; Navajas Navarro, Maria; Niere, Björn; Parnell, Stephen; Potting, Roel; Rafoss, Trond; Rossi, Vittorio; Urek, Gregor; Van Bruggen, Ariena; Van der Werf, Wopke; West, Jonathan; Winter, Stephan; Kertész, Virág; Aukhojee, Mitesha; Grégoire, Jean‐ClaudeJeger, Michael; Bragard, Claude; Caffier, David; Candresse, Thierry; Chatzivassiliou, Elisavet; Dehnen‐schmutz, Katharina; Gilioli, Gianni; Jaques Miret, Josep Anton; Macleod, Alan; Navajas Navarro, Maria; Niere, Björn; Parnell, Stephen; Potting, Roel; Rafoss, Trond; Rossi, Vittorio; Urek, Gregor; Van Bruggen, Ariena; Van der Werf, Wopke; West, Jonathan; Winter, Stephan; Kertész, Virág; Aukhojee, Mitesha; Grégoire, Jean‐claud

Pest categorisation of Toxoptera citricida

23The European Commission requested EFSA to conduct a pest categorisation of Toxoptera citricida (Hemiptera: Aphididae), an oligophagous aphid developing and reproducing parthenogenetically on tender leaf and flower flush of citrus (Rutaceae). T.citricida is a taxonomic entity with reliable methods available for detection and identification. It is regulated in the EU by Council Directive 2000/29/EC where it is listed in Annex IIAI as a harmful organism whose introduction and spread into the EU shall be banned. T.citricida is native to tropical regions of Southeast Asia and has spread to most citrus-growing areas worldwide, except California and the Mediterranean basin, causing significant damage to citrus as it is the most efficient vector of the Citrus tristeza virus (CTV). T.citricida occurs in Madeira and, with a restricted distribution, in the north-west of the Iberian Peninsula, mostly on backyard citrus trees. This may have hindered the effectiveness of the official control measures in these areas. There are further phytosanitary measures in place in the EU in order to limit entry via traded commodities. Citrus plants for planting are regulated and are a closed pathway. However, there is uncertainty regarding host status of some non-rutaceous plants on which this aphid has been recorded and so other plant genera may provide additional pathways. The EFSA Plant Health Panelconcludes that the establishment of T.citricida in the main EU citrus growing areas around the Mediterranean would have significant impacts because of its ability to vector CTV. Considering the criteria within the remit of EFSA to assess the status as a potential Union quarantine pest (QP), as a potential protected zone quarantine pest (PZQP) or as a potential regulated non-quarantine pest (RNQP), T.citricida meets with no uncertainties the criteria assessed by EFSA for consideration as a potential Union QP.openopenJeger, Michael; Bragard, Claude; Caffier, David; Candresse, Thierry; Chatzivassiliou, Elisavet; Dehnen‐Schmutz, Katharina; Gilioli, Gianni; Grégoire, Jean‐Claude; Jaques Miret, Josep Anton; Navarro, Maria Navajas; Niere, Björn; Parnell, Stephen; Potting, Roel; Rafoss, Trond; Rossi, Vittorio; Urek, Gregor; Van Bruggen, Ariena; Van der Werf, Wopke; West, Jonathan; Winter, Stephan; Gardi, Ciro; Bergeretti, Filippo; MacLeod, AlanJeger, Michael; Bragard, Claude; Caffier, David; Candresse, Thierry; Chatzivassiliou, Elisavet; Dehnen‐schmutz, Katharina; Gilioli, Gianni; Grégoire, Jean‐claude; Jaques Miret, Josep Anton; Navarro, Maria Navajas; Niere, Björn; Parnell, Stephen; Potting, Roel; Rafoss, Trond; Rossi, Vittorio; Urek, Gregor; Van Bruggen, Ariena; Van der Werf, Wopke; West, Jonathan; Winter, Stephan; Gardi, Ciro; Bergeretti, Filippo; Macleod, Ala

Pest categorisation of Scirtothrips citri

The Panel on Plant Health performed a pest categorisation of the citrus thrips, Scirtothrips citri (Moulton) (Thysanoptera: Thripidae), for the European Union (EU). This is a well-de fi ned and distinguishable species, occurring in North America and Asia. Its precise distribution in Asia is uncertain. S. citri is a pest of citrus and blueberries and has been cited on over 50 different host species in 33 plant families. Whether all plants reported as hosts are true hosts, allowing population development of S. citri , is uncertain. S. citri feeds exclusively on young actively growing foliage and fruit. It is not known to occur in the EU and is listed in Annex IIAI of 2000/29/EC as a harmful organism. The international trade of hosts, as either plants for planting or cut fl owers, provide potential pathways into the EU. However, current EU legislation prohibits the import of citrus plants for planting. Furthermore, measures aimed at the import of plants for planting in a dormant stage (no young foliage or fruits present) with no soil/growing medium attached, decreases the likelihood of the pest ’ s entry via other hosts. Considering that there are regional climatic similarities where S. citri occurs in the USA with climates in the EU, and taking EU host distribution into account, S. citri has the potential to establish in the EU, especially in citrus and blueberry growing regions around the Mediterranean where quality losses in citrus and yield losses in blueberry could occur. Phytosanitary measures are available to inhibit the likelihood of introduction of S. citri from infested countries. Considering the criteria within the remit of EFSA to assess its status as a potential Union quarantine pest (QP) or as a potential regulated non-quarantine pest (RNQP), S. citri meets with no uncertainties the criteria assessed by EFSA for consideration as a potential Union QP