Investigating the role of Wnt signaling effectors on the neuron-glia switch and OPC specification during development and after injury.

PROJECT SUMMARY Nervous system development and regeneration relies on sequential and coordinated formation of diverse neurons and glia from neural progenitor cells. Though neuronal and glial differentiation is extensively studied, less is known about the molecular signals that modulate the transition from neurogenesis to gliogenesis. Oligodendrocytes, glial cells that support axon conduction and survival through myelination, are essential for nervous system development and regeneration. During spinal cord development, distinct neural progenitors in the pMN domain undergo a neuron-glia switch to sequentially produce motor neurons followed by oligodendrocyte progenitor cells (OPCs). Similarly, successful regeneration after spinal cord injury requires the coordinated production of both neurons and oligodendrocytes to functionally restore damaged circuits. Zebrafish are highly regenerative compared to mammals and endogenous neural progenitors produce motor neurons after injury, but interestingly do not produce OPCs. The molecular mechanisms that regulate the neuron-glia switch to specify neural progenitor cells into a neuronal or oligodendrocyte fate during development and after injury remain unknown. Recently, our lab conducted fate mapping and single-cell RNAseq and revealed a molecularly distinct subset of pMN neural progenitors, pre-OPCs, that are specified to commit to the oligodendrocyte lineage. Our data revealed that pre-OPCs are uniquely enriched for factors involved in Wnt signaling, a cascade that modulates OPC differentiation during development and that is reactivated after injury to regulate neurogenesis. Using zebrafish, I will utilize immunohistochemistry and transgenic imaging techniques alongside CRISPR/Cas9 mutagenesis strategies to determine how axin1 modulates wnt expression in pMN progenitors to activate a transcriptional switch in tcf7l2 and drive a neuron-glia switch to specify pMN progenitor cells into pre-OPCs. Further, through powerful single-cell multi-omics techniques I will identify transcriptional interactions with neuronal and oligodendrocyte-specific genes in pMN progenitors to establish a gene regulatory network that drives the neuron-glia switch. Finally, I will use pharmacological and genetic tools to manipulate wnt expression after spinal cord injury and induce a neuron-glia switch in vivo to drive gliogenesis in endogenous neural progenitor cells. Together, these studies will uncover molecular regulators of pMN progenitor specification and highlight the role of the neuron-glia switch in nervous system development and regeneration.