A simple and effective genotyping workflow for rapid detection of CRISPR genome editing

Genetically engineered mouse models play a pivotal role in the modeling of diseases, exploration of gene functions, and the development of novel therapies. In recent years, clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein 9 (Cas9)-mediated genome editing technology has revolutionized the process of developing such models by enabling precise genome modifications of the multiple interested genes simultaneously. Following genome editing, an efficient genotyping methodology is crucial for subsequent characterization. However, current genotyping methods are laborious, time-consuming, and costly. Here, using targeting the mouse trypsinogen genes as an example, we introduced common applications of CRISPR-Cas9 editing and a streamlined cost-effective genotyping workflow for CRISPR-edited mouse models, in which Sanger sequencing is required only at the initial steps. In the F0 mice, we focused on identifying the presence of positive editing by PCR followed by Sanger sequencing without the need to know the exact sequences, simplifying the initial screening. In the F1 mice, Sanger sequencing and algorithms decoding were used to identify the precise editing. Once the edited sequence was established, a simple and effective genotyping strategy was established to distinguish homozygous and heterozygous status by PCR from tail DNA. The genotyping workflow applies to deletions as small as one nucleotide, multiple-gene knockout, and knockin studies. This simplified, efficient, and cost-effective genotyping shall be instructive to new investigators who are unfamiliar with characterizing CRISPR-Cas9-edited mouse strains.NEW & NOTEWORTHY This study presents a streamlined, cost-effective genotyping workflow for clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein 9 (Cas9) edited mouse models, focusing on trypsinogen genes. It simplifies initial F0 mouse screening using PCR and Sanger sequencing without needing exact sequences. For F1 mice, precise editing is identified through Sanger sequencing and algorithm decoding. The workflow includes a novel PCR strategy for distinguishing homozygous and heterozygous statuses in subsequent generations, effective for small deletions, multiple-gene knockouts, and knockins.

GetPrimers: A generalized PCR-based genetic targeting primer designer enabling easy and standardized targeted gene modification across multiple systems

Genetic targeting (e.g., gene knockout and tagging) based on polymerase chain reaction (PCR) is a simple yet powerful approach for studying gene functions. Although originally developed in classic budding and fission yeast models, the same principle applies to other eukaryotic systems with efficient homologous recombination. One-step PCR-based genetic targeting is conventionally used but the sizes of the homologous arms that it generates for recombination-mediated genetic targeting are usually limited. Alternatively, gene targeting can also be performed via fusion PCR, which can create homologous arms that are orders of magnitude larger, therefore substantially increasing the efficiency of recombination-mediated genetic targeting. Here, we present GetPrimers (https://www.evomicslab.org/app/getprimers/), a generalized computational framework and web tool to assist automatic targeting and verification primer design for both one-step PCR-based and fusion PCR-based genetic targeting experiments. Moreover, GetPrimers by design runs for any given genetic background of any species with full genome scalability. Therefore, GetPrimers is capable of empowering high-throughput functional genomic assays at multipopulation and multispecies levels. Comprehensive experimental validations have been performed for targeting and verification primers designed by GetPrimers across multiple organism systems and experimental setups. We anticipate GetPrimers to become a highly useful and popular tool to facilitate easy and standardized gene modification across multiple systems.

Reconsidering the role of blood-brain barrier in Alzheimer's disease: From delivery to target

The existence of a selective blood-brain barrier (BBB) and neurovascular coupling are two unique central nervous system vasculature features that result in an intimate relationship between neurons, glia, and blood vessels. This leads to a significant pathophysiological overlap between neurodegenerative and cerebrovascular diseases. Alzheimer's disease (AD) is the most prevalent neurodegenerative disease whose pathogenesis is still to be unveiled but has mostly been explored under the light of the amyloid-cascade hypothesis. Either as a trigger, bystander, or consequence of neurodegeneration, vascular dysfunction is an early component of the pathological conundrum of AD. The anatomical and functional substrate of this neurovascular degeneration is the BBB, a dynamic and semi-permeable interface between blood and the central nervous system that has consistently been shown to be defective. Several molecular and genetic changes have been demonstrated to mediate vascular dysfunction and BBB disruption in AD. The isoform ε4 of Apolipoprotein E is at the same time the strongest genetic risk factor for AD and a known promoter of BBB dysfunction. Low-density lipoprotein receptor-related protein 1 (LRP-1), P-glycoprotein, and receptor for advanced glycation end products (RAGE) are examples of BBB transporters implicated in its pathogenesis due to their role in the trafficking of amyloid-β. This disease is currently devoid of strategies that change the natural course of this burdening illness. This unsuccess may partly be explained by our misunderstanding of the disease pathogenesis and our inability to develop drugs that are effectively delivered to the brain. BBB may represent a therapeutic opportunity as a target itself or as a therapeutic vehicle. In this review, we aim to explore the role of BBB in the pathogenesis of AD including the genetic background and detail how it can be targeted in future therapeutic research.

A perspective on astrocyte regulation of neural circuit function and animal behavior

Studies over the past two decades have demonstrated that astrocytes are tightly associated with neurons and play pivotal roles in neural circuit development, operation, and adaptation in health and disease. Nevertheless, precisely how astrocytes integrate diverse neuronal signals, modulate neural circuit structure and function at multiple temporal and spatial scales, and influence animal behavior or disease through aberrant excitation and molecular output remains unclear. This Perspective discusses how new and state-of-the-art approaches, including fluorescence indicators, opto- and chemogenetic actuators, genetic targeting tools, quantitative behavioral assays, and computational methods, might help resolve these longstanding questions. It also addresses complicating factors in interpreting astrocytes’ role in neural circuit regulation and animal behavior, such as their heterogeneity, metabolism, and inter-glial communication. Research on these questions should provide a deeper mechanistic understanding of astrocyte-neuron assemblies’ role in neural circuit function, complex behaviors, and disease.

A Chemogenetic Approach for the Optical Monitoring of Voltage in Neurons

Optical monitoring of neuronal voltage using fluorescent indicators is a powerful approach for the interrogation of the cellular and molecular logic of the nervous system. Herein, a semisynthetic tethered voltage indicator (STeVI1) based upon nile red is described that displays voltage sensitivity when genetically targeted to neuronal membranes. This environmentally sensitive probe allows for wash-free imaging and faithfully detects supra- and sub-threshold activity in neurons.

Mechanosensory neurons control the timing of spinal microcircuit selection during locomotion

Despite numerous physiological studies about reflexes in the spinal cord, the contribution of mechanosensory feedback to active locomotion and the nature of underlying spinal circuits remains elusive. Here we investigate how mechanosensory feedback shapes active locomotion in a genetic model organism exhibiting simple locomotion-the zebrafish larva. We show that mechanosensory feedback enhances the recruitment of motor pools during active locomotion. Furthermore, we demonstrate that inputs from mechanosensory neurons increase locomotor speed by prolonging fast swimming at the expense of slow swimming during stereotyped acoustic escape responses. This effect could be mediated by distinct mechanosensory neurons. In the spinal cord, we show that connections compatible with monosynaptic inputs from mechanosensory Rohon-Beard neurons onto ipsilateral V2a interneurons selectively recruited at high speed can contribute to the observed enhancement of speed. Altogether, our study reveals the basic principles and a circuit diagram enabling speed modulation by mechanosensory feedback in the vertebrate spinal cord.

Noncanonical connections between the subiculum and hippocampal CA1

The hippocampal formation is traditionally viewed as having a feedforward, unidirectional circuit organization that promotes propagation of excitatory processes. While the substantial forward projection from hippocampal CA1 to the subiculum has been very well established, accumulating evidence supports the existence of a significant backprojection pathway comprised of both excitatory and inhibitory elements from the subiculum to CA1. Based on these recently updated anatomical connections, such a backprojection could serve to modulate information processing in hippocampal CA1. Here we review the published anatomical and physiological studies on the subiculum to CA1 backprojection, and present recent conclusive anatomical evidence for the presence of noncanonical subicular projections to CA1. New insights into this understudied pathway will improve our understanding of reciprocal CA1-subicular connections and guide future studies on how the subiculum interacts with CA1 to regulate hippocampal circuit activity and learning and memory behaviors. J. Comp. Neurol. 524:3666-3673, 2016. © 2016 The Authors The Journal of Comparative Neurology Published by Wiley Periodicals, Inc.

Multiplexed modular genetic targeting of quantum dots

While DNA-directed nanotechnology is now a well-established platform for bioinspired nanoscale assembly in vitro, the direct targeting of various nanomaterials in living biological systems remains a significant challenge. Hybrid biological systems with integrated and targeted nanomaterials may have interesting and exploitable properties, so methods for targeting various nanomaterials to precise biological locations are required. Fluorescence imaging has benefited from the use of nanoparticles with superior optical properties compared to fluorescent organic dyes or fluorescent proteins. While single-particle tracking (SPT) in living cells with genetically encoded proteins is limited to very short trajectories, the high photon output of genetically targeted and multiplexed quantum dots (QDs) would enable long-trajectory analysis of multiple proteins. However, challenges with genetic targeting of QDs limit their application in these experiments. In this report, we establish a modular method for targeting QD nanoparticles selectively to multiple genetically encoded tags by precomplexing QD-streptavidin conjugates with cognate biotinylated hapten molecules. This approach enables labeling and SPT of multiple genetically encoded proteins on living cells at high speed and can label expressed proteins in the cytosol upon microinjection into living cells. While we demonstrate labeling with three distinct QD conjugates, the approach can be extended to other specific hapten-affinity molecule interactions and alternative nanoparticles, enabling precise directed targeting of nanoparticles in living biological systems.

Presynaptic inhibition of gamma-aminobutyric acid release in the bed nucleus of the stria terminalis by kappa opioid receptor signaling

BACKGROUND

The kappa opioid receptor (KOR) and its endogenous agonist, the neuropeptide dynorphin, are a critical component of the central stress system. Both dynorphin and KOR are expressed in the bed nucleus of the stria terminalis (BNST), a brain region associated with anxiety and stress. This suggests that KOR activation in this region may play a role in the regulation of emotional behaviors. To date, however, there has been no investigation of the ability of KOR to modulate synaptic transmission in the BNST.

METHODS

We used whole-cell patch-clamp recordings from acutely prepared mouse brain slices to examine the actions of KOR on inhibitory transmission in the BNST. Additionally, we used neurochemical and pathway-specific optogenetic manipulations to selectively stimulate gamma-aminobutyric acid (GABA)ergic fibers from the central nucleus of the amygdala (CeA) to the BNST.

RESULTS

We found that activation of KOR reduced GABAergic transmission through a presynaptic mechanism. Furthermore, we examined the signal transduction pathways that mediate this inhibition and provide the first functional information implicating extracellular signal-regulated kinase in KOR-mediated presynaptic modulation. Moreover, we found that at KOR signaling robustly reduced inhibitory synaptic transmission in the CeA to BNST pathway.

CONCLUSIONS

Together, these results demonstrate that KOR provides important inhibitory control over presynaptic GABAergic signaling within the BNST and provides the first direct functional demonstration of KOR-sensitive long-range GABAergic connections between the CeA and the BNST.