Rapid and Sparse Labeling of Neurons Based on the Mutant Virus-Like Particle of Semliki Forest Virus

Virus-Based Neural Circuit Tracing

Neural circuits provide an anatomical basis for functional networks. Therefore, dissecting the structure of neural circuits is an indispensable prerequisite to understanding how the brain functions. Knowing how the neural circuits organize and function under physiological conditions and their progressive alterations under pathophysiological conditions are key to understanding the underlying circuit mechanism of diseases, thus finding cures for the diseases. Recombinant neurotropic viruses are important tools for neural circuit tracing with many advantages over non-viral tracers: they allow for anterograde, retrograde, and trans-synaptic delivery of tracers in a cell-type-specific, circuit-selective manner. We herein summarize the recent developments in the viral tools for neural circuit tracing, discuss the key principles of using viral tools in neuroscience research, and highlight innovations for developing and optimizing viral tools for neural circuit tracing across diverse animal species, including nonhuman primates.

O-GlcNAcylation Is Required for the Survival of Cerebellar Purkinje Cells by Inhibiting ROS Generation

Purkinje cells (PCs), as a unique type of neurons output from the cerebellar cortex, are essential for the development and physiological function of the cerebellum. However, the intricate mechanisms underlying the maintenance of Purkinje cells are unclear. The O-GlcNAcylation (O-GlcNAc) of proteins is an emerging regulator of brain function that maintains normal development and neuronal circuity. In this study, we demonstrate that the O-GlcNAc transferase (OGT) in PCs maintains the survival of PCs. Furthermore, a loss of OGT in PCs induces severe ataxia, extensor rigidity and posture abnormalities in mice. Mechanistically, OGT regulates the survival of PCs by inhibiting the generation of intracellular reactive oxygen species (ROS). These data reveal a critical role of O-GlcNAc signaling in the survival and maintenance of cerebellar PCs.

Single-Cell Labeling Strategies to Dissect Neuronal Structures and Local Functions

The brain network consists of ten billion neurons and is the most complex structure in the universe. Understanding the structure of complex brain networks and neuronal functions is one of the main goals of modern neuroscience. Since the seminal invention of Golgi staining, single-cell labeling methods have been among the most potent approaches for dissecting neuronal structures and neural circuits. Furthermore, the development of sparse single-cell transgenic methods has enabled single-cell gene knockout studies to examine the local functions of various genes in neural circuits and synapses. Here, we review non-transgenic single-cell labeling methods and recent advances in transgenic strategies for sparse single neuronal labeling. These methods and strategies will fundamentally contribute to the understanding of brain structure and function.

Viral Tools for Neural Circuit Tracing

Neural circuits provide an anatomical basis for functional networks. Therefore, dissecting the structure of neural circuits is essential to understanding how the brain works. Recombinant neurotropic viruses are important tools for neural circuit tracing with many advantages over non-viral tracers: they allow for anterograde, retrograde, and trans-synaptic delivery of tracers in a cell type-specific, circuit-selective manner. In this review, we summarize the recent developments in the viral tools for neural circuit tracing, discuss the key principles of using viral tools in neuroscience research, and highlight innovations for developing and optimizing viral tools for neural circuit tracing across diverse animal species, including nonhuman primates.

In vivo cell tracking with viral vector mediated genetic labeling

Cell tracking is a useful technique to monitor specific cell populations for their morphology, development, proliferation, migration, interaction, function, and other properties, both in vitro and in vivo. Using different materials and methodologies to label the target cells directly or indirectly, the dynamic biological processes in living organisms can be visualized with appropriate detection techniques. Viruses, with the unique ability to deliver exogenous genes into host cells, have been used as vectors to mediate gene transfer. Genetic labeling of target cells by viral vectors endows the cells to express reporter genes with high efficiency and specificity. In conjunction with corresponding imaging techniques, cells labeled with different genetic reporters mediated by different viral vectors can be monitored across spatial and temporal scales to fulfill various purposes and address different questions. In the present review, we introduce the basic principle of viral vectors in cell tracking and highlight the examples of cell tracking in various research areas.

Interrogating autonomic peripheral nervous system neurons with viruses - A literature review

How rich functionality emerges from the rather invariant structural architecture of the peripheral autonomic nervous system remains one of the major mysteries in neuroscience. The high incidence of patients with neural circuit-related autonomic nervous system diseases highlights the importance of fundamental research, among others with neurotracing methods, into autonomic neuron functionality. Due to the emergence of neurotropic virus-based tracing techniques in recent years the access to neuronal connectivity in the peripheral autonomic nervous system has greatly been improved. This review is devoted to the anatomical distribution of neural circuits in the periphery of the autonomous nervous system and to the interaction between the autonomic nervous system and vital peripheral organs or tissues. The experimental evidence available at present has greatly expanded our understanding of autonomic peripheral nervous system neurons.

Scalable volumetric imaging for ultrahigh-speed brain mapping at synaptic resolution

The speed of high-resolution optical imaging has been a rate-limiting factor for meso-scale mapping of brain structures and functional circuits, which is of fundamental importance for neuroscience research. Here, we describe a new microscopy method of Volumetric Imaging with Synchronized on-the-fly-scan and Readout (VISoR) for high-throughput, high-quality brain mapping. Combining synchronized scanning beam illumination and oblique imaging over cleared tissue sections in smooth motion, the VISoR system effectively eliminates motion blur to obtain undistorted images. By continuously imaging moving samples without stopping, the system achieves high-speed 3D image acquisition of an entire mouse brain within 1.5 hours, at a resolution capable of visualizing synaptic spines. A pipeline is developed for sample preparation, imaging, 3D image reconstruction and quantification. Our approach is compatible with immunofluorescence methods, enabling flexible cell-type specific brain mapping and is readily scalable for large biological samples such as primate brains. Using this system, we examined behaviorally relevant whole-brain neuronal activation in 16 c-Fos-shEGFP mice under resting or forced swimming conditions. Our results indicate the involvement of multiple subcortical areas in stress response. Intriguingly, neuronal activation in these areas exhibits striking individual variability among different animals, suggesting the necessity of sufficient cohort size for such studies.

Optimization of the Fluorescent Protein Expression Level Based on Pseudorabies Virus Bartha Strain for Neural Circuit Tracing

Mapping the neural circuits facilitates understanding the brain’s working mechanism. Pseudorabies virus (PRV; Bartha stain) as a tracer can infect neurons and retrogradely transport in neural circuits. To illuminate the network, tracers expressing reporter genes at a high level are needed. In this study, we optimized the expression level of reporter genes and constructed two new retrograde trans-multisynaptic tracers PRV531 and PRV724, which separately express more robust green and red fluorescent proteins than the existing retrograde tracers PRV152 and PRV614. PRV531 and PRV724 can be used for mapping the neural circuit of the central nervous system (CNS) and the peripheral nervous system (PNS). Overall, our work adds two valuable tracers to the toolbox for mapping neural circuits.