SARM1 Inhibition in Three Mouse Models of Charcot-Marie-Tooth Disease.

Background: Charcot-Marie-Tooth (CMT) disease can be caused by mutations in over 100 different genes, most of which lead to demyelination (type 1) or degeneration (type 2) of peripheral motor and sensory axons. SARM1 is a protein involved in the active process of Wallerian degeneration after axonal injury. Inhibition of SARM1 protects against axon degeneration following injury or in cases such as chemotherapy-induced peripheral neuropathy.

Inhibitory G proteins play multiple roles to polarize sensory hair cell morphogenesis.

Inhibitory G alpha (GNAI or Gαi) proteins are critical for the polarized morphogenesis of sensory hair cells and for hearing. The extent and nature of their actual contributions remains unclear, however, as previous studies did not investigate all GNAI proteins and included non-physiological approaches. Pertussis toxin can downregulate functionally redundant GNAI1, GNAI2, GNAI3, and GNAO proteins, but may also induce unrelated defects.

Lack of effect from genetic deletion of Hdac6 in a humanized mouse model of CMT2D.

Background: Inhibition of HDAC6 has been proposed as a broadly applicable therapeutic strategy for Charcot-Marie-Tooth disease (CMT). Inhibition of HDAC6 increases the acetylation of proteins important in axonal trafficking, such as α-tubulin and Miro, and has been shown to be efficacious in several preclinical studies using mouse models of CMT.

Aims: Here, we sought to expand on previous preclinical studies by testing the effect of genetic deletion of Hdac6 on mice carrying a humanized knockin allele of Gars1, a model of CMT-type 2D.

Dominant mutations causing axonal Charcot-Marie-Tooth disease expand -associated diseases.

Pathogenic variants in six aminoacyl-tRNA synthetase (ARS) genes are implicated in neurological disorders, most notably inherited peripheral neuropathies. ARSs are enzymes that charge tRNA molecules with cognate amino acids. Pathogenic variants in asparaginyl-tRNA synthetase () cause a neurological phenotype combining developmental delay, ataxia and demyelinating peripheral neuropathy.

Testing SIPA1L2 as a modifier of CMT1A using mouse models.

Charcot-Marie-Tooth disease type 1A (CMT1A) is a demyelinating peripheral neuropathy caused by the duplication of peripheral myelin protein 22 (PMP22), leading to muscle weakness and loss of sensation in the hands and feet. A recent case-only genome-wide association study of CMT1A patients conducted by the Inherited Neuropathy Consortium identified a strong association between strength of foot dorsiflexion and variants in signal induced proliferation associated 1 like 2 (SIPA1L2), indicating that it may be a genetic modifier of disease. To validate SIPA1L2 as a candidate modifier and to assess its potential as a therapeutic target, we engineered mice with deletion of exon 1 (including the start codon) of the Sipa1l2 gene and crossed them to the C3-PMP22 mouse model of CMT1A.

Misregulation of mitochondria-lysosome contact dynamics in Charcot-Marie-Tooth Type 2B disease Rab7 mutant sensory peripheral neurons.

Inter-organelle contact sites between mitochondria and lysosomes mediate the crosstalk and bidirectional regulation of their dynamics in health and disease. However, mitochondria-lysosome contact sites and their misregulation have not been investigated in peripheral sensory neurons. Charcot-Marie-Tooth type 2B disease is an autosomal dominant axonal neuropathy affecting peripheral sensory neurons caused by mutations in the GTPase Rab7.

An allelic series of spontaneous Rorb mutant mice exhibit a gait phenotype, changes in retina morphology and behavior, and gene expression signatures associated with the unfolded protein response.

The Retinoid-related orphan receptor beta (RORβ) gene encodes a developmental transcription factor and has 2 predominant isoforms created through alternative first exon usage; one specific to the retina and another present more broadly in the central nervous system, particularly regions involved in sensory processing. RORβ belongs to the nuclear receptor family and plays important roles in cell fate specification in the retina and cortical layer formation. In mice, loss of RORβ causes disorganized retina layers, postnatal degeneration, and production of immature cone photoreceptors.

Precision mouse models of Yars/dominant intermediate Charcot-Marie-Tooth disease type C and Sptlc1/hereditary sensory and autonomic neuropathy type 1.

Animal models of neurodegenerative diseases such as inherited peripheral neuropathies sometimes accurately recreate the pathophysiology of the human disease, and sometimes accurately recreate the genetic perturbations found in patients. Ideally, models achieve both, but this is not always possible; nonetheless, such models are informative. Here we describe two animal models of inherited peripheral neuropathy: mice with a mutation in tyrosyl tRNA-synthetase, Yars , modeling dominant intermediate Charcot-Marie-Tooth disease type C (diCMTC), and mice with a mutation in serine palmitoyltransferase long chain 1, Sptlc1 , modeling hereditary sensory and autonomic neuropathy type 1 (HSAN1).

tRNA overexpression rescues peripheral neuropathy caused by mutations in tRNA synthetase.

Heterozygous mutations in six transfer RNA (tRNA) synthetase genes cause Charcot-Marie-Tooth (CMT) peripheral neuropathy. CMT mutant tRNA synthetases inhibit protein synthesis by an unknown mechanism. We found that CMT mutant glycyl-tRNA synthetases bound tRNA but failed to release it, resulting in tRNA sequestration.

T Cells from NOD- Mice Target Both Pancreatic and Neuronal Tissue.

It has become increasingly appreciated that autoimmune responses against neuronal components play an important role in type 1 diabetes (T1D) pathogenesis. In fact, a large proportion of islet-infiltrating B lymphocytes in the NOD mouse model of T1D produce Abs directed against the neuronal type III intermediate filament protein peripherin. NOD- mice are a previously developed BCR-transgenic model in which virtually all B lymphocytes express the H and L chain Ig molecules from the intra-islet-derived anti-peripherin-reactive hybridoma H280.

Model validity for preclinical studies in precision medicine: precisely how precise do we need to be?

The promise of personalized medicine is that each patient's treatment can be optimally tailored to their disease. In turn, their disease, as well as their response to the treatment, is determined by their genetic makeup and the "environment," which relates to their general health, medical history, personal habits, and surroundings. Developing such optimized treatment strategies is an admirable goal and success stories include examples such as switching chemotherapy agents based on a patient's tumor genotype.

GPSM2-GNAI Specifies the Tallest Stereocilia and Defines Hair Bundle Row Identity.

The transduction compartment of inner ear hair cells, the hair bundle, is composed of stereocilia rows of graded height, a property essential for sensory function that remains poorly understood at the molecular level. We previously showed that GPSM2-GNAI is enriched at stereocilia distal tips and required for their postnatal elongation and bundle morphogenesis-two characteristics shared with MYO15A (short isoform), WHRN, and EPS8 proteins. Here we first performed a comprehensive genetic analysis of the mouse auditory epithelium to show that GPSM2, GNAI, MYO15A, and WHRN operate in series within the same pathway.

A spontaneous mouse deletion in Mctp1 uncovers a long-range cis-regulatory region crucial for NR2F1 function during inner ear development.

Hundreds of thousands of cis-regulatory DNA sequences are predicted in vertebrate genomes, but unlike genes themselves, few have been characterized at the functional level or even unambiguously paired with a target gene. Here we serendipitously identified and started investigating the first reported long-range regulatory region for the Nr2f1 (Coup-TFI) transcription factor gene. NR2F1 is temporally and spatially regulated during development and required for patterning and regionalization in the nervous system, including sensory hair cell organization in the auditory epithelium of the cochlea.

The Spindle Orientation Machinery Beyond Mitosis: When Cell Specialization Demands Polarization.

Mitosis is a process requiring strict spatial organization of cellular components. In particular, the orientation of the mitotic spindle with respect to the tissue defines the division plane. In turn, the orientation of cell division can regulate tissue morphology or the fate of daughter cells.

A link between planar polarity and staircase-like bundle architecture in hair cells.

Sensory perception in the inner ear relies on the hair bundle, the highly polarized brush of movement detectors that crowns hair cells. We previously showed that, in the mouse cochlea, the edge of the forming bundle is defined by the 'bare zone', a microvilli-free sub-region of apical membrane specified by the Insc-LGN-Gαi protein complex. We now report that LGN and Gαi also occupy the very tip of stereocilia that directly abut the bare zone.

DSCAMs: restoring balance to developmental forces.

Many of the models of neurodevelopmental processes such as cell migration, axon outgrowth, and dendrite arborization involve cell adhesion and chemoattraction as critical physical or mechanical aspects of the mechanism. However, the prevention of adhesion or attraction is under-appreciated as a necessary, active process that balances these forces, insuring that the correct cells are present and adhering in the correct place at the correct time. The phenomenon of not adhering is often viewed as the passive alternative to adhesion, and in some cases this may be true.

Contact is repulsive, but please note the "enclosed".

Previous models of neuronal dendrite arborization suggested that contact-dependent self-avoidance between dendrite branches prevents self-crossings within the arbor. Two papers in Neuron show how integrin-mediated adhesion to the extracellular matrix restricts dendrites to a two-dimensional space to optimize this mechanism (Han et al., 2012; Kim et al.

A spontaneous mutation in contactin 1 in the mouse.

Mutations in the gene encoding the immunoglobulin-superfamily member cell adhesion molecule contactin1 (CNTN1) cause lethal congenital myopathy in human patients and neurodevelopmental phenotypes in knockout mice. Whether the mutant mice provide an accurate model of the human disease is unclear; resolving this will require additional functional tests of the neuromuscular system and examination of Cntn1 mutations on different genetic backgrounds that may influence the phenotype. Toward these ends, we have analyzed a new, spontaneous mutation in the mouse Cntn1 gene that arose in a BALB/c genetic background.

Loss of Bardet-Biedl syndrome protein-8 (BBS8) perturbs olfactory function, protein localization, and axon targeting.

Bardet-Biedl syndrome (BBS) is a pleiotropic, heterogeneous human disease whose etiology lies primarily in dysfunctional basal bodies and/or cilia. Both BBS patients and several BBS mouse models exhibit impaired olfactory function. To explore the nature of olfactory defects in BBS, a genetic ablation of the mouse Bbs8 gene that incorporates a fluorescent reporter protein was created.