Elucidating the diverse identities of oligodendrocyte precursor cells

It has long been known that central nervous system (CNS) neurons are a diverse cell population, but in recent years it has also become clear that non-neuronal support cells of the CNS, summarised as ‘glia’, exhibit diverse properties and functions. One particular type of glia is called the oligodendrocyte precursor cell (OPC), which has established roles in giving rise to myelinating oligodendrocytes during long-term development, as a form of CNS plasticity, and in myelin regeneration. OPCs can do so because they exist throughout the CNS lifelong, comprising approximately 5% of all CNS cells. However, despite their abundance, it is also apparent that not all OPCs contribute to myelination with equal efficiency. Understanding how new myelin can be recruited from the OPC pool is an important question for both neurodevelopmental and regenerative myelination. Work over the past decade has revealed that OPCs have diverse properties. However, we do not understand what this diversity reflects. One major reason for this lack of knowledge is that there is a notorious lack of markers to categorise different OPCs at any point in time, and lack of knowledge to predict their properties and functions. The other reason is that OPC properties can change over time, and we have only very limited understanding of the relationships between OPC subgroups with different properties. Here, we propose to address these problems through newly generated zebrafish knock-in reporter lines for two identified markers of OPC subpopulations. In a first step, we will carry out clonal analysis of OPC dynamics across the entire CNS using in vivo imaging methods to monitor how OPCs transition between marker identities, and how this relates to the production of new myelinating oligodendrocytes. In a second step, we will manipulate the generation of new oligodendrocytes in experimental models of myelin regeneration and of myelin plasticity to test how OPC subpopulations with different marker identities respond to these different triggers to generate new myelin. The results obtained from this work will push forward the frontiers of bioscience discovery from several perspectives. Firstly, the implementation of CRISPR reporter knock-ins in zebrafish for in vivo lineage tracing will showcase the power of this approach to unambiguously test cell lineage relationships, which is crucial for our understanding of all biological processes. Within our field of oligodendrocyte and myelin biology, we will provide principally new knowledge on how the oligodendrocyte lineage is organised. Beyond the immediate goals of this proposal, we will generate knowledge with implications for animal and human health as it may help tailoring informed strategies to drive the myelination process where it is inefficient.