Expression data from purified medial ganglionic eminence (MGE) interneurons, 3 biological replicates

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. We used microarrays to generate a list of expressed genes in purified medial ganglionic eminence (MGE) interneurons E13 MGE tissue was dissected from CD1 embryos and cultured as described (Tsui et al., 2014). Briefly, embryos were maintained on ice in Hank’s balanced salt solution (HBSS, Gibco) during dissection. Following removal of the cortex and meninges to expose the ventral forebrain, MGE tissue was excised and mechanically triturated in Neurobasal medium (Gibco) containing 40 ng/ml FGF2 (BD Biosciences), 2% B27 supplement (Gibco), and 500 µM L-Glutamine (Gibco). Triturated MGE cells were plated on to four-well chamber slides (Nunc) pre-coated with 2% laminin (BD Biosciences) and 1% poly-D-lysine (Sigma) at a density of 59,000 cells/cm2. On day 5 of culture, 1 μM cytosine β arabinofuranoside C (AraC, Sigma) was added. After 24h of AraC treatment, the medium was changed 3 times at 2h intervals to wash out the AraC and dead cells. Purified MGE neurons were then cultured for 2 additional days.