Transplantation of GABAergic interneurons (INs) can provide long-term functional benefits in animal models of epilepsy and other neurological disorders. Whereas GABAergic INs can be differentiated from embryonic stem cells, alternative sources of GABAergic INs may be more tractable for disease modeling and transplantation. We identified five factors (Foxg1, Sox2, Ascl1, Dlx5, and Lhx6) that convert mouse fibroblasts into induced GABAergic INs (iGABA-INs) possessing molecular signatures of telencephalic INs. Factor overexpression activates transcriptional networks required for GABAergic fate specification. iGABA-INs display progressively maturing firing patterns comparable to cortical INs, form functional synapses, and release GABA. Importantly, iGABA-INs survive and mature upon being grafted into mouse hippocampus. Optogenetic stimulation demonstrated functional integration of grafted iGABA-INs into host circuitry, triggering inhibition of host granule neuron activity. These five factors also converted human cells into functional GABAergic INs. These properties suggest that iGABA-INs have potential for disease modeling and cell-based therapeutic approaches to neurological disorders.
SummaryNeural networks are emerging as the fundamental computational unit of the brain and it is becoming progressively clearer that network dysfunction is at the core of a number of psychiatric and neurodegenerative disorders. Yet, our ability to target specific networks for functional or genetic manipulations remains limited. Monosynaptically restricted rabies virus facilitates the anatomical investigation of neural circuits. However, the inherent cytotoxicity of the rabies largely prevents its implementation in long-term functional studies and the genetic manipulation of neural networks. To overcome this limitation, we developed a self-inactivating ΔG-rabies virus (SiR) that transcriptionally disappears from the infected neurons while leaving permanent genetic access to the traced network. SiR provides a virtually unlimited temporal window for the study of network dynamics and for the genetic and functional manipulation of neural circuits in vivo without adverse effects on neuronal physiology and circuit function.
Genetically encoded fluorescent proteins and immunostaining are widely used to detect cellular and subcellular structures in fixed biological samples. However, for thick or whole-mount tissue, each approach suffers from limitations, including limited spectral flexibility and lower signal or slow speed, poor penetration, and high background labeling, respectively. We have overcome these limitations by using transgenically expressed chemical tags for rapid, even, highsignal and low-background labeling of thick biological tissues. We first construct a platform of widely applicable transgenic Drosophila reporter lines, demonstrating that chemical labeling can accelerate staining of whole-mount fly brains by a factor of 100. Using viral vectors to deliver chemical tags into the mouse brain, we then demonstrate that this labeling strategy works well in mice. Thus this tag-based approach drastically improves the speed and specificity of labeling genetically marked cells in intact and/or thick biological samples.immunohistochemistry | neural circuits | protein labeling | fluorescence microscopy T he revolution in live imaging resulting from the use of genetically encoded fluorescent proteins (FPs) is widely appreciated (1, 2), but FPs also have had a major impact on studies of fixed, whole-mount specimens or thick sections. Processing of large or intact pieces of tissue has obvious advantages over sectioning, such as reduced tissue damage, compatibility with fast imaging modalities (e.g., light sheet microscopy), and easy subsequent 3D reconstruction. The drastic increase in imaging throughput by using whole-mount brains had a major impact on Drosophila neurobiology, in which reconstruction of neural circuits is a key requirement. Recently, several methods have been developed that allow whole-mount imaging of the mouse brain: CLARITY (3), Scale (4), SeeDB (5), and CUBIC (6) all render the brain optically transparent (although to different degrees). In such samples, imaging the native fluorescence of genetically encoded FPs offers the advantages of immediate visualization, low background, and spatially even signal. However, FP signals are easily quenched by fixation or other staining procedures, suffer from limited spectral flexibility, and often emit weak signals. Therefore, antibody detection of marker proteins remains essential in many experimental situations. Immunostaining, however, is notoriously slow, highly nonlinear, and often results in uneven labeling with high background levels. Therefore, there are undesirable tradeoffs in the antibody vs. FP labeling techniques.These tradeoffs are a major practical issue for our research in neural circuit tracing in Drosophila (7-12). We therefore sought staining methods that combine the positive aspects of both FPs and antibody-based staining, notably fast, even, strong, and spectrally diverse signals with low background labeling. We have developed an approach based on four commercially available, orthogonal labeling chemistries (SNAP-, CLIP-, Halo-and TMP-tag) characteriz...
We develop an approach to tag proteomes synthesized by specific cell types in dissociated cortex, brain slices, and the brains of live mice. By viral-mediated expression of an orthogonal pyrrolysyl-tRNA synthetase-tRNAXXX pair in a cell type of interest and providing a non-canonical amino acid with a chemical handle, we selectively label neuronal or glial proteomes. The method enables the identification of proteins from spatially and genetically defined regions of the brain.
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