MBL-1 and EEL-1 affect the splicing and protein levels of MEC-3 to control dendrite complexity.

Transcription factors (TFs) play critical roles in specifying many aspects of neuronal cell fate including dendritic morphology. How TFs are accurately regulated during neuronal morphogenesis is not fully understood. Here, we show that LIM homeodomain protein MEC-3, the key TF for C. elegans PVD dendrite morphogenesis, is regulated by both alternative splicing and an E3 ubiquitin ligase. The mec-3 gene generates several transcripts by alternative splicing. We find that mbl-1, the orthologue of the muscular dystrophy disease gene muscleblind-like (MBNL), is required for PVD dendrite arbor formation. Our data suggest mbl-1 regulates the alternative splicing of mec-3 to produce its long isoform. Deleting the long isoform of mec-3(deExon2) causes reduction of dendrite complexity. Through a genetic modifier screen, we find that mutation in the E3 ubiquitin ligase EEL-1 suppresses mbl-1 phenotype. eel-1 mutants also suppress mec-3(deExon2) mutant but not the mec-3 null phenotype. Loss of EEL-1 alone leads to excessive dendrite branches. Together, these results indicate that MEC-3 is fine-tuned by alternative splicing and the ubiquitin system to produce the optimal level of dendrite branches.

New Therapeutic Landscape in Neuromyelitis Optica.

PURPOSE OF REVIEW: This review discusses the current treatment trends and emerging therapeutic landscape for patients with neuromyelitis optica spectrum disorder (NMOSD). RECENT FINDINGS: Conventional immune suppressive therapies, such as B cell depletion, have been used for long-term treatment. However, the availability of recent FDA-approved and investigational drugs has made therapeutic choices for NMOSD more complex. SUMMARY: Recent randomized clinical trials have shown that eculizumab, inebilizumab, and satralizumab are efficacious therapies for AQP4 seropositive NMOSD. These therapies may not have the same benefit in patients with seronegative NMOSD, including MOG-associated disease, and further investigation is required in this population. Reliable biomarkers to guide therapy decisions are urgently needed. There is a plethora of promising investigational therapies currently in the pipeline with exciting and novel mechanisms of action.

Case series: Hearing loss in neuromyelitis optica spectrum disorders.

BACKGROUND: Aquaporin 4 (AQP4)- and myelin oligodendrocyte glycoprotein (MOG)-associated neuromyelitis optica spectrum disorders (NMOSD) are thought to primarily affect the central nervous system (CNS). However, emerging evidence suggests that there are extra-CNS manifestations of NMOSD, including myopathies, gastrointestinal dysfunction, renal involvement and adverse pregnancy outcomes.1 METHODS: Three patients who reported hearing loss during a NMOSD relapse were identified through a retrospective case review. RESULTS: In this article, we discuss two AQP4-IgG positive NMOSD cases, each presenting with conductive and sensorineural hearing loss, and a case of MOG-IgG-associated NMOSD presenting with sensorineural hearing loss. CONCLUSION: Hearing loss may be present as a relapse in patients with NMOSD. Early recognition and timely treatment are essential to prevent irreversible hearing loss.

A case of GFAP-astroglial autoimmunity presenting with reversible parkinsonism.

Autoimmune glial fibrillary acidic protein (GFAP) astrocytopathy is a newly recognized autoimmune central nervous system (CNS) inflammatory disorder, presenting with an array of neurological symptoms in association with autoantibodies against GFAP, a hallmark protein expressed on astrocytes. Limited knowledge is available on the disease pathogenesis and clinical outcome. Here, we report a case of autoimmune GFAP astrocytopathy presenting with encephalomyelitis and parkinsonism. Our patient was a 66-year old male who experienced progressive somnolence, apathy, anxiety, right arm tremor, urinary retention, progressive weakness, and falls over the course of three months, followed by acute delusional psychosis. His neurologic exam on hospital admission was notable for cognitive impairment, myoclonus, rigidity, right hand action tremor, bradykinesia, shuffling gait, and dysmetria. Cerebrospinal fluid examination showed elevated protein, lymphocytic pleocytosis, and one unique oligoclonal band. Magnetic resonance imaging (MRI) revealed non-specific T2/FLAIR hyperintensities in the brain and longitudinally extensive transverse myelitis in the cervical spine. FDG-PET showed a pattern of brain uptake suspicious for limbic encephalitis. Serum and CSF paraneoplastic panel showed presence of GFAP immunoglobulin G (IgG). Treatment with corticosteroids resulted in clinical and radiographic improvement. However, the patient was treated with anti-CD20 immunotherapy due to steroid-dependence. This case exemplifies the recently described neurologic syndrome of autoimmune GFAP astrocytopathy presenting with encephalomyelitis and parkinsonism, reversed by B lymphocyte depletion.

A multi-protein receptor-ligand complex underlies combinatorial dendrite guidance choices in C. elegans.

Ligand receptor interactions instruct axon guidance during development. How dendrites are guided to specific targets is less understood. The C. elegans PVD sensory neuron innervates muscle-skin interface with its elaborate dendritic branches. Here, we found that LECT-2, the ortholog of leukocyte cell-derived chemotaxin-2 (LECT2), is secreted from the muscles and required for muscle innervation by PVD. Mosaic analyses showed that LECT-2 acted locally to guide the growth of terminal branches. Ectopic expression of LECT-2 from seam cells is sufficient to redirect the PVD dendrites onto seam cells. LECT-2 functions in a multi-protein receptor-ligand complex that also contains two transmembrane ligands on the skin, SAX-7/L1CAM and MNR-1, and the neuronal transmembrane receptor DMA-1. LECT-2 greatly enhances the binding between SAX-7, MNR-1 and DMA-1. The activation of DMA-1 strictly requires all three ligands, which establishes a combinatorial code to precisely target and pattern dendritic arbors.

MTM-6, a phosphoinositide phosphatase, is required to promote synapse formation in Caenorhabditis elegans.

Forming the proper number of synapses is crucial for normal neuronal development. We found that loss of function of the phosphoinositide phosphatase mtm-6 results in a reduction in the number of synaptic puncta. The reduction in synapses is partially the result of MTM-6 regulation of the secretion of the Wnt ligand EGL-20 from cells in the tail and partially the result of neuronal action. MTM-6 shows relative specificity for EGL-20 over the other Wnt ligands. We suggest that the ability of MTM-6 to regulate EGL-20 secretion is a function of its expression pattern. We conclude that regulation of secretion of different Wnt ligands can use different components. Additionally, we present a novel neuronal function for MTM-6.

Caenorhabditis elegans Muscleblind homolog mbl-1 functions in neurons to regulate synapse formation.

BACKGROUND: The sequestration of Muscleblind splicing regulators results in myotonic dystrophy. Previous work on Muscleblind has largely focused on its roles in muscle development and maintenance due to the skeletal and cardiac muscle degeneration phenotype observed in individuals with the disorder. However, a number of reported nervous system defects suggest that Muscleblind proteins function in other tissues as well. RESULTS: We have identified a mutation in the Caenorhabditis elegans homolog of Muscleblind, mbl-1, that is required for proper formation of neuromuscular junction (NMJ) synapses. mbl-1 mutants exhibit selective loss of the most distal NMJ synapses in a C. elegans motorneuron, DA9, visualized using the vesicle-associated protein RAB-3, as well as the active zone proteins SYD-2/liprin-α and UNC-10/Rim. The proximal NMJs appear to have normal pre- and postsynaptic specializations. Surprisingly, expressing a mbl-1 transgene in the presynaptic neuron is sufficient to rescue the synaptic defect, while muscle expression has no effect. Consistent with this result, mbl-1 is also expressed in neurons. CONCLUSIONS: Based on these results, we conclude that in addition to its functions in muscle, the Muscleblind splice regulators also function in neurons to regulate synapse formation.