Winkler, C. C. | bioRxiv Science

bioRxiv2020

Unraveling the transcriptional networks that drive oligodendrocyte fate specification in Sonic hedgehog-responsive neocortical progenitors

In the developing nervous system, progenitors first generate neurons before making astrocytes and oligodendrocytes. We previously showed that increased Sonic hedgehog (Shh) signaling in dorsal forebrain progenitors is important for their production of oligodendrocytes as neurogenesis winds down. Here, we analyzed single-cell RNA sequencing datasets to better understand how Shh controls this neuron-to-oligodendrocyte switch in the neocortex. We first identified Shh-responding progenitors using a dataset in which Shh was overexpressed in the mouse dorsal forebrain. Pseudotime trajectory inferences revealed a subpopulation committed to the oligodendrocyte precursor cell (OPC) lineage. Genes upregulated along this lineage defined a pre-OPC state, as cells transitioned from progenitors to OPCs. Using several datasets from wild-type mouse and human embryos at different ages, we confirmed a pre-OPC state preceding OPC emergence during normal development. Finally, we show that pre-OPCs are enriched for a gene regulatory network involving the transcription factor Ascl1. Genetic lineage-tracing demonstrated Ascl1+ dorsal progenitors primarily make oligodendrocytes. We propose a model in which Shh shifts the balance between opposing transcriptional networks toward an Ascl1 lineage, thereby facilitating the switch between neurogenesis and oligodendrogenesis.

developmental biology↗

bioRxiv2019

Loss of Shh signaling in the neocortex reveals heterogeneous cell recovery responses from distinct oligodendrocyte populations

The majority of oligodendrocytes in the neocortex originate from neural progenitors that reside in the dorsal forebrain. We recently showed that Sonic Hedgehog (Shh) signaling in these dorsal progenitors is required to produce normal numbers of neocortical oligodendrocytes during embryonic development. Conditional deletion of the Shh signaling effector, Smo, in dorsal progenitors caused a dramatic reduction in oligodendrocyte numbers in the embryonic neocortex. In the current study, we show that the depleted oligodendrocyte lineage in Smo conditional mutants is able to recover to control numbers over time. This eventual recovery is achieved in part by expansion of the ventrally-derived wild-type lineage that normally makes up a minority of the total oligodendrocyte population. However, we find that the remaining dorsally-derived mutant cells also increase in numbers over time to contribute equally to the recovery of the total population. Additionally, we found that the ways in which the dorsal and ventral sources cooperate to achieve recovery is different for distinct subclasses of oligodendrocyte-lineage cells. Oligodendrocyte precursor cells (OPCs) in the neocortical white matter recover completely by expansion of the remaining dorsally-derived Smo mutant cells. On the other hand, mature oligodendrocytes in the white and gray matter recover through an equal contribution from dorsal mutant and ventral wild-type lineages. Interestingly, the only population that did not make a full recovery was OPCs in the gray matter. We find that gray matter OPCs are less proliferative in Smo cKO mutants compared to controls, which may explain their inability to fully recover. These studies shed light on the nature of competition and cooperation between dorsal and ventral sources of oligodendrocytes in the developing neocortex. Furthermore, our data point towards differential use of Shh signaling in the development of distinct subclasses of the oligodendrocyte lineage.

neuroscience↗