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Model organism (MO) research provides a basic understanding of biology and disease due to the evolutionary conservation of the molecular and cellular language of life. MOs have been used to identify and understand the function of orthologous genes, proteins, cells and tissues involved in biological processes, to develop and evaluate techniques and methods, and to perform whole-organism-based chemical screens to test drug efficacy and toxicity. However, a growing richness of datasets and the rising power of computation raise an important question: How do we maximize the value of MOs? In-depth discussions in over 50 virtual presentations organized by the National Institutes of Health across more than 10 weeks yielded important suggestions for improving the rigor, validation, reproducibility and translatability of MO research. The effort clarified challenges and opportunities for developing and integrating tools and resources. Maintenance of critical existing infrastructure and the implementation of suggested improvements will play important roles in maintaining productivity and facilitating the validation of animal models of human biology and disease.

The move from reading to writing the human genome offers new opportunities to improve human health. The United States National Institutes of Health (NIH) Somatic Cell Genome Editing (SCGE) Consortium aims to accelerate the development of safer and more-effective methods to edit the genomes of disease-relevant somatic cells in patients, even in tissues that are difficult to reach. Here we discuss the consortium's plans to develop and benchmark approaches to induce and measure genome modifications, and to define downstream functional consequences of genome editing within human cells. Central to this effort is a rigorous and innovative approach that requires validation of the technology through third-party testing in small and large animals. New genome editors, delivery technologies and methods for tracking edited cells in vivo, as well as newly developed animal models and human biological systems, will be assembled-along with validated datasets-into an SCGE Toolkit, which will be disseminated widely to the biomedical research community. We visualize this toolkit-and the knowledge generated by its applications-as a means to accelerate the clinical development of new therapies for a wide range of conditions.

Notch signaling is a highly conserved intercellular pathway with tightly regulated and pleiotropic roles in normal tissue development and homeostasis. Dysregulated Notch signaling has also been implicated in human disease, including multiple forms of cancer, and represents an emerging therapeutic target. Successful development of such therapeutics requires a detailed understanding of potential on-target toxicities. Here, we identify autosomal dominant mutations of the canonical Notch ligand Jagged1 (or JAG1) as a cause of peripheral nerve disease in 2 unrelated families with the hereditary axonal neuropathy Charcot-Marie-Tooth disease type 2 (CMT2). Affected individuals in both families exhibited severe vocal fold paresis, a rare feature of peripheral nerve disease that can be life- threatening. Our studies of mutant protein posttranslational modification and localization indicated that the mutations (p.Ser577Arg, p.Ser650Pro) impair protein glycosylation and reduce JAG1 cell surface expression. Mice harboring heterozygous CMT2-associated mutations exhibited mild peripheral neuropathy, and homozygous expression resulted in embryonic lethality by midgestation. Together, our findings highlight a critical role for JAG1 in maintaining peripheral nerve integrity, particularly in the recurrent laryngeal nerve, and provide a basis for the evaluation of peripheral neuropathy as part of the clinical development of Notch pathway-modulating therapeutics., Introduction The Notch pathway is a highly conserved cell-cell signaling mechanism that functions in virtually all tissues to regulate multiple aspects of cell fate and homeostasis. Dysregulation of Notch signaling [...]

Blood-CNS barrier disruption is a hallmark of numerous neurological disorders, yet whether barrier breakdown is sufficient to trigger neurodegenerative disease remains unresolved. Therapeutic strategies to mitigate barrier hyperpermeability are also limited. Dominant missense mutations of the cation channel transient receptor potential vanilloid 4 (TRPV4) cause forms of hereditary motor neuron disease. To gain insights into the cellular basis of these disorders, we generated knock-in mouse models of TRPV4 channelopathy by introducing two disease-causing mutations (R269C and R232C) into the endogenous mouse Trpv4 gene. TRPV4 mutant mice exhibited weakness, early lethality, and regional motor neuron loss. Genetic deletion of the mutant Trpv4 allele from endothelial cells (but not neurons, glia, or muscle) rescued these phenotypes. Symptomatic mutant mice exhibited focal disruptions of blood–spinal cord barrier (BSCB) integrity, associated with a gain of function of mutant TRPV4 channel activity in neural vascular endothelial cells (NVECs) and alterations of NVEC tight junction structure. Systemic administration of a TRPV4-specific antagonist abrogated channel-mediated BSCB impairments and provided a marked phenotypic rescue of symptomatic mutant mice. Together, our findings show that mutant TRPV4 channels can drive motor neuron degeneration in a non–cell autonomous manner by precipitating focal breakdown of the BSCB. Further, these data highlight the reversibility of TRPV4-mediated BSCB impairments and identify a potential therapeutic strategy for patients with TRPV4 mutations. Editor's summary: TRPV4 (transient receptor potential vanilloid 4) is a mechanosensitive cation channel important for vascular function. TRPV4 mutations have been identified in patients with motor neuropathies, but it is unknown how functional alternations in this channel drive neurodegeneration. Sullivan et al. show that mice with gain-of-function mutations in Trpv4 developed progressive neurological symptoms that were associated with blood–spinal cord barrier breakdown and focal loss of motor neurons. Removal of Trpv4 from endothelial cells (but not other cell types) or treatment with a small molecule antagonist reversed pathology. These findings reveal a cascade of events that potentially drives neurodegeneration in TRPV4 channelopathies. —Daniela Neuhofer [ABSTRACT FROM AUTHOR]

Mitofusin-2 (MFN2) is a mitochondrial outer-membrane protein that plays a pivotal role in mitochondrial dynamics in most tissues, yet mutations in MFN2, which cause Charcot-Marie-Tooth disease type 2A (CMT2A), primarily affect the nervous system. We generated a transgenic mouse model of CMT2A that developed severe early onset vision loss and neurological deficits, axonal degeneration without cell body loss, and cytoplasmic and axonal accumulations of fragmented mitochondria. While mitochondrial aggregates were labeled for mitophagy, mutant MFN2 did not inhibit Parkin-mediated degradation, but instead had a dominant negative effect on mitochondrial fusion only when MFN1 was at low levels, as occurs in neurons. Finally, using a transgenic approach, we found that augmenting the level of MFN1 in the nervous system in vivo rescued all phenotypes in mutant [MFN2.sup.R94Q]-expressing mice. These data demonstrate that the MFN1/MFN2 ratio is a key determinant of tissue specificity in CMT2A and indicate that augmentation of MFN1 in the nervous system is a viable therapeutic strategy for the disease., Introduction Mitofusin-2 (MFN2) is a mitochondrial GTPase that plays a pivotal role in mitochondrial dynamics, including regulation of mitochondrial fusion, transport, mitophagy, mtDNA stability, and mitochondria-ER interactions (1-5). Given the [...]

Gene editing in the brain has been challenging because of the restricted transport imposed by the blood-brain barrier (BBB). Current approaches mainly rely on local injection to bypass the BBB. However, such administration is highly invasive and not amenable to treating certain delicate regions of the brain. We demonstrate a safe and effective gene editing technique by using focused ultrasound (FUS) to transiently open the BBB for the transport of intravenously delivered CRISPR/Cas9 machinery to the brain. [ABSTRACT FROM AUTHOR]

Spinal muscular atrophy (SMA) is a common neuromuscular disorder in humans. In fact, it is the most frequently inherited cause of infant mortality, being the result of mutations in the survival of motor neuron 1 (SMN1) gene that reduce levels of SMN protein. Restoring levels of SMN protein in individuals with SMA is perceived to be a viable therapeutic option, but the efficacy of such a strategy once symptoms are apparent has not been determined. We have generated mice harboring an inducible Smn rescue allele and used them in a model of SMA to investigate the effects of turning on SMN expression at different time points during the course of the disease. Restoring SMN protein even after disease onset was sufficient to reverse neuromuscular pathology and effect robust rescue of the SMA phenotype. Importantly, our findings also indicated that there was a therapeutic window of opportunity from P4 through P8 defined by the extent of neuromuscular synapse pathology and the ability of motor neurons to respond to SMN induction, following which restoration of the protein to the organism failed to produce therapeutic benefit. Nevertheless, our results suggest that even in severe SMA, timely reinstatement of the SMN protein may halt the progression of the disease and serve as an effective postsymptomatic treatment., Introduction Spinal muscular atrophy (SMA) is a common (~1:6400 newborns), often fatal, pediatric neuromuscular disorder caused by mutations in the survival of the motor neuron 1 (SMN1) gene (1) and, [...]

The brain activity of a mutant mice was studied by inducing a slow-wave epilepsy phenotype. Results show that there is a neoronal cell death in the mutant mice's cerebellum and brainstem. The sodium-hydrogen exchanger (NHE1) is proven to play an important role in detecting gene defects in the slow-wave epilepsy. However, the beginning and severity of slow-wave epilepsy depends on the genetic background of the mice.

An alpha(sub 1A) voltage-sensitive calcium-channel gene that is mutated in the mouse tottering (tg and tg(super la)) locus is identified to be involved in absence epilepsy. Mutations at the tg locus cause a neurological disorder manifested by ataxia, motor seizures and behavioral absence seizures that resemble petit mal epilepsy in humans. A slow, selective degeneration of cerebellar neurons is also manifested by a more severe allele, leaner tg(super la). These results represent the first mutations in a mammalian central nervous system-specific voltage-sensitive calcium channel and mark the first time that a gene involved in absence epilepsy is identified.

Immunohistochemistry of the generalized and tonic-clonic epilepsies in recombinant inbred mouse strains SWXL-4 reveals that seizure induces defective activation of c-Jun and c-Fos gene products in limbic and cortical structures and causes bilateral high frequency spike cortical discharges and quiescent post-ictal phase. SWXL-L outcrosses with other inbred strains, leading to F1 hybrid formation that reveals a seizure frequency determinant Szf1 close to the pink-eyed dilution locus on chromosome 7 that is responsible for 32% of genetic variation in the F2 hybrids. A genetic epilepsy model simulates these data from the study of common mouse strains.