C1ql1 expression in oligodendrocyte progenitor cells promotes oligodendrocyte differentiation.

Myelinating oligodendrocytes arise from the stepwise differentiation of oligodendrocyte progenitor cells (OPCs). Approximately 5% of all adult brain cells are OPCs. Why would a mature brain need such a large number of OPCs? New myelination is possibly required for higher-order functions such as cognition and learning. Additionally, this pool of OPCs represents a source of new oligodendrocytes to replace those lost during injury, inflammation, or in diseases such as multiple sclerosis (MS). How OPCs are instructed to differentiate into oligodendrocytes is poorly understood, and for reasons presently unclear, resident pools of OPCs are progressively less utilized in MS. The complement component 1, q subcomponent-like (C1QL) protein family has been studied for their functions at neuron-neuron synapses, but we show that OPCs express C1ql1. We created OPC-specific conditional knockout mice and show that C1QL1 deficiency reduces the differentiation of OPCs into oligodendrocytes and reduces myelin production during both development and recovery from cuprizone-induced demyelination. In vivo over-expression of C1QL1 causes the opposite phenotype: increased oligodendrocyte density and myelination during recovery from demyelination. We further used primary cultured OPCs to show that C1QL1 levels can bidirectionally regulate the extent of OPC differentiation in vitro. Our results suggest that C1QL1 may initiate a previously unrecognized signaling pathway to promote differentiation of OPCs into oligodendrocytes. This study has relevance for possible novel therapies for demyelinating diseases and may illuminate a previously undescribed mechanism to regulate the function of myelination in cognition and learning.

Creation of a novel CRISPR-generated allele to express HA epitope-tagged C1QL1 and improved methods for its detection at synapses.

C1QL1 is expressed in a subset of cells in the brain and likely has pleiotropic functions, including the regulation of neuron-to-neuron synapses. Research progress on C1QL proteins has been slowed by a dearth of available antibodies. Therefore, we created a novel knock-in mouse line in which an HA-tag is inserted into the endogenous C1ql1 locus. We examined the entire brain, identifying previously unappreciated nuclei expressing C1QL1, presumably in neurons. By total numbers, however, the large majority of C1QL1-expressing cells are of the oligodendrocyte lineage. Subcellular immunolocalization of synaptic cleft proteins is challenging, so we developed a new protocol to improve signal at synapses. Lastly, we compared various anti-HA antibodies to assist future investigations using this and likely other HA epitope-tagged alleles.