Probes for INS

Abstract

During development, newborn interneurons migrate throughout the embryonic brain. Here, we provide evidence that these interneurons act in a paracrine fashion to regulate developmental oligodendrocyte formation. Specifically, we show that medial ganglionic eminence (MGE) interneurons secrete factors that promote genesis of oligodendrocytes from glially biased cortical precursors in culture. Moreover, when MGE interneurons are genetically ablated in vivo prior to their migration, this causes a deficit in cortical oligodendrogenesis. Modeling of the interneuron-precursor paracrine interaction using transcriptome data identifies the cytokine fractalkine as responsible for the pro-oligodendrocyte effect in culture. This paracrine interaction is important in vivo, since knockdown of the fractalkine receptor CX3CR1 in embryonic cortical precursors, or constitutive knockout of CX3CR1, causes decreased numbers of oligodendrocyte progenitor cells (OPCs) and oligodendrocytes in the postnatal cortex. Thus, in addition to their role in regulating neuronal excitability, interneurons act in a paracrine fashion to promote the developmental genesis of oligodendrocytes.

Traumatic brain injury (TBI) commonly results in injury to the components of the white matter tracts, causing post-injury cognitive deficits. The myelin-producing oligodendrocytes (OLs) are vulnerable to TBI although may plausibly be replaced by proliferating oligodendrocyte progenitor cells (OPCs). The cytokine interleukin-1β (IL-1β) is a key mediator of the complex inflammatory response, and when neutralized in experimental TBI behavioral outcome was improved. To evaluate the role of IL-1β on OL cell death and OPC proliferation, 116 adult male mice subjected to sham injury or the central fluid percussion injury (cFPI) model of traumatic axonal injury, were analyzed at 2, 7 and 14 days post-injury. At 30 min post-injury, mice were randomly assigned to receiving an IL-1β neutralizing or a control antibody. OPC proliferation (5-ethynyl 2´- deoxyuridine (EdU)/Olig2 co-labeling) and mature OL cell loss was evaluated in injured white matter tracts. Microglia immunohistochemistry and ramification using Sholl analysis was also evaluated. Neutralizing IL-1β resulted in attenuated cell death, indicated by cleaved caspase-3 expression, and reduced loss of mature OLs from 2-7 days post-injury in brain-injured animals. IL-1β neutralization also attenuated the early, 2 day post-injury, increase of microglial immunoreactivity and the change in their ramification. However, the proliferation of OPCs in brain-injured animals was not altered. Our data suggest that IL-1β is involved in the TBI-induced loss of OLs and early microglial activation, although not the OPC proliferation. Attenuated oligodendrocyte cell loss may contribute to the improved behavioral outcome observed by IL-1β neutralization in this mouse model of diffuse TBI.

Nervous system function depends on proper myelination for insulation and critical trophic support for axons. Myelination is tightly regulated spatially and temporally, but how it is controlled molecularly remains largely unknown. Here, we identified key molecular mechanisms governing the regional and temporal specificity of CNS myelination. We show that transcription factor EB (TFEB) is highly expressed by differentiating oligodendrocytes and that its loss causes precocious and ectopic myelination in many parts of the murine brain. TFEB functions cell-autonomously through PUMA induction and Bax-Bak activation to promote programmed cell death of a subset of premyelinating oligodendrocytes, allowing selective elimination of oligodendrocytes in normally unmyelinated brain regions. This pathway is conserved across diverse brain areas and is critical for myelination timing. Our findings define an oligodendrocyte-intrinsic mechanism underlying the spatiotemporal specificity of CNS myelination, shedding light on how myelinating glia sculpt the nervous system during development.