G protein-coupled receptor 37-like 1 modulates astrocyte glutamate transporters and neuronal NMDA receptors and is neuroprotective in ischemia.

We show that the G protein-coupled receptor GPR37-like 1 (GPR37L1) is expressed in most astrocytes and some oligodendrocyte precursors in the mouse central nervous system. This contrasts with GPR37, which is mainly in mature oligodendrocytes. Comparison of wild type and Gpr37l1-/- mice showed that loss of GPR37L1 did not affect the input resistance or resting potential of astrocytes or neurons in the hippocampus. However, GPR37L1-mediated signalling inhibited astrocyte glutamate transporters and - surprisingly, given its lack of expression in neurons - reduced neuronal NMDA receptor (NMDAR) activity during prolonged activation of the receptors as occurs in ischemia. This effect on NMDAR signalling was not mediated by a change in the release of D-serine or TNF-α, two astrocyte-derived agents known to modulate NMDAR function. After middle cerebral artery occlusion, Gpr37l1 expression was increased around the lesion. Neuronal death was increased by ∼40% in Gpr37l1-/- brain compared to wild type in an in vitro model of ischemia. Thus, GPR37L1 protects neurons during ischemia, presumably by modulating extracellular glutamate concentration and NMDAR activation.

Combining Double Fluorescence In Situ Hybridization with Immunolabelling for Detection of the Expression of Three Genes in Mouse Brain Sections.

Detection of gene expression in different types of brain cells e.g., neurons, astrocytes, oligodendrocytes, oligodendrocyte precursors and microglia, can be hampered by the lack of specific primary or secondary antibodies for immunostaining. Here we describe a protocol to detect the expression of three different genes in the same brain section using double fluorescence in situ hybridization with two gene-specific probes followed by immunostaining with an antibody of high specificity directed against the protein encoded by a third gene. The Aspartoacyclase (ASPA) gene, mutations of which can lead to a rare human white matter disease - Canavan disease - is thought to be expressed in oligodendrocytes and microglia but not in astrocytes and neurons. However, the precise expression pattern of ASPA in the brain has yet to be established. This protocol has allowed us to determine that ASPA is expressed in a subset of mature oligodendrocytes and it can be generally applied to a wide range of gene expression pattern studies.

An Fgfr3-iCreER(T2) transgenic mouse line for studies of neural stem cells and astrocytes.

The lack of markers for astrocytes, particularly gray matter astrocytes, significantly hinders research into their development and physiological properties. We previously reported that fibroblast growth factor receptor 3 (Fgfr3) is expressed by radial precursors in the ventricular zone of the embryonic neural tube and subsequently by differentiated astrocytes in gray and white matter. Here, we describe an Fgfr3-iCreER(T2) phage artificial chromosome transgenic mouse line that allows efficient tamoxifen-induced Cre recombination in Fgfr3-expressing cells, including radial glial cells in the embryonic neural tube and both fibrous and protoplasmic astrocytes in the mature central nervous system. This mouse strain will therefore be useful for studies of normal astrocyte biology and their responses to CNS injury or disease. In addition, Fgfr3-iCreER(T2) drives Cre recombination in all neurosphere-forming stem cells in the adult spinal cord and at least 90% of those in the adult forebrain subventricular zone. We made use of this to show that there is continuous accumulation of all major interneuron subtypes in the olfactory bulb (OB) from postnatal day 50 (P50) until at least P230 ( approximately 8 months of age). It therefore seems likely that adult-born interneurons integrate into existing circuitry and perform long-term functions in the adult OB.

Specification of CNS glia from neural stem cells in the embryonic neuroepithelium.

All the neurons and glial cells of the central nervous system are generated from the neuroepithelial cells in the walls of the embryonic neural tube, the 'embryonic neural stem cells'. The stem cells seem to be equivalent to the so-called 'radial glial cells', which for many years had been regarded as a specialized type of glial cell. These radial cells generate different classes of neurons in a position-dependent manner. They then switch to producing glial cells (oligodendrocytes and astrocytes). It is not known what drives the neuron-glial switch, although downregulation of pro-neural basic helix-loop-helix transcription factors is one important step. This drives the stem cells from a neurogenic towards a gliogenic mode. The stem cells then choose between developing as oligodendrocytes or astrocytes, of which there might be intrinsically different subclasses. This review focuses on the different extracellular signals and intracellular responses that influence glial generation and the choice between oligodendrocyte and astrocyte fates.

Oligodendrocyte wars.

Oligodendrocyte precursors first arise in a restricted ventral part of the embryonic spinal cord and migrate laterally and dorsally from there. Later, secondary sources develop in the dorsal cord. Normally, the ventrally-derived precursors compete with and suppress their dorsal counterparts. There are also ventral and dorsal sources in the forebrain, but here the more dorsal precursors prevail and the ventral-most lineage is eliminated during postnatal life. How do the different populations compete and what is the outcome of the competition? Do different embryonic origins signify different functional subgroups of oligodendrocyte?

Fgfr3 expression by astrocytes and their precursors: evidence that astrocytes and oligodendrocytes originate in distinct neuroepithelial domains.

The postnatal central nervous system (CNS) contains many scattered cells that express fibroblast growth factor receptor 3 transcripts (Fgfr3). They first appear in the ventricular zone (VZ) of the embryonic spinal cord in mid-gestation and then distribute into both grey and white matter - suggesting that they are glial cells, not neurones. The Fgfr3(+) cells are interspersed with but distinct from platelet-derived growth factor receptor alpha (Pdgfra)-positive oligodendrocyte progenitors. This fits with the observation that Fgfr3 expression is preferentially excluded from the pMN domain of the ventral VZ where Pdgfra(+) oligodendrocyte progenitors--and motoneurones--originate. Many glial fibrillary acidic protein (Gfap)- positive astrocytes co-express Fgfr3 in vitro and in vivo. Fgfr3(+) cells within and outside the VZ also express the astroglial marker glutamine synthetase (Glns). We conclude that (1) Fgfr3 marks astrocytes and their neuroepithelial precursors in the developing CNS and (2) astrocytes and oligodendrocytes originate in complementary domains of the VZ. Production of astrocytes from cultured neuroepithelial cells is hedgehog independent, whereas oligodendrocyte development requires hedgehog signalling, adding further support to the idea that astrocytes and oligodendrocytes can develop independently. In addition, we found that mice with a targeted deletion in the Fgfr3 locus strongly upregulate Gfap in grey matter (protoplasmic) astrocytes, implying that signalling through Fgfr3 normally represses Gfap expression in vivo.