A Comprehensive Review of Neuromuscular Manifestations of COVID-19 and Management of Pre-Existing Neuromuscular Disorders in Children

Since the emergence of SARS-CoV-2, several studies have been published describing neuromuscular manifestations of the disease, as well as management of pre-existing pediatric neuromuscular disorders during the COVID-19 pandemic. These disorders include muscular dystrophies, myasthenic syndromes, peripheral nerve disorders, and spinal muscular atrophy. Such patients are a vulnerable population due to frequent complications such as scoliosis, cardiomyopathy, and restrictive lung disease that put them at risk of severe complications of COVID-19. In this review, neuromuscular manifestations of COVID-19 in children and the management of pre-existing pediatric neuromuscular disorders during the COVID-19 pandemic are discussed. We also review strategies to alleviate pandemic-associated disruptions in clinical care and research, including the emerging role of telemedicine and telerehabilitation to address the continued special needs of these patients

Patronin-mediated minus end growth is required for dendritic microtubule polarity.

Microtubule minus ends are thought to be stable in cells. Surprisingly, in Drosophila and zebrafish neurons, we observed persistent minus end growth, with runs lasting over 10 min. In Drosophila, extended minus end growth depended on Patronin, and Patronin reduction disrupted dendritic minus-end-out polarity. In fly dendrites, microtubule nucleation sites localize at dendrite branch points. Therefore, we hypothesized minus end growth might be particularly important beyond branch points. Distal dendrites have mixed polarity, and reduction of Patronin lowered the number of minus-end-out microtubules. More strikingly, extra Patronin made terminal dendrites almost completely minus-end-out, indicating low Patronin normally limits minus-end-out microtubules. To determine whether minus end growth populated new dendrites with microtubules, we analyzed dendrite development and regeneration. Minus ends extended into growing dendrites in the presence of Patronin. In sum, our data suggest that Patronin facilitates sustained microtubule minus end growth, which is critical for populating dendrites with minus-end-out microtubules

A unified in vitro evaluation for apatite-forming ability of bioactive glasses and their variants

The aim of this study was to propose and validate a new unified method for testing dissolution rates of bioactive glasses and their variants, and the formation of calcium phosphate layer formation on their surface, which is an indicator of bioactivity. At present, comparison in the literature is difficult as many groups use different testing protocols. An ISO standard covers the use of simulated body fluid on standard shape materials but it does not take into account that bioactive glasses can have very different specific surface areas, as for glass powders. Validation of the proposed modified test was through round robin testing and comparison to the ISO standard where appropriate. The proposed test uses fixed mass per solution volume ratio and agitated solution. The round robin study showed differences in hydroxyapatite nucleation on glasses of different composition and between glasses of the same composition but different particle size. The results were reproducible between research facilities. Researchers should use this method when testing new glasses, or their variants, to enable comparison between the literature in the future

Cryo EM Analysis Reveals Inherent Flexibility of Authentic Murine Papillomavirus Capsids

Human papillomavirus (HPV) is a significant health burden and leading cause of virus-induced cancers. However, studies have been hampered due to restricted tropism that makes production and purification of high titer virus problematic. This issue has been overcome by developing alternative HPV production methods such as virus-like particles (VLPs), which are devoid of a native viral genome. Structural studies have been limited in resolution due to the heterogeneity, fragility, and stability of the VLP capsids. The mouse papillomavirus (MmuPV1) presented here has provided the opportunity to study a native papillomavirus in the context of a common laboratory animal. Using cryo EM to solve the structure of MmuPV1, we achieved 3.3 Å resolution with a local symmetry refinement method that defined smaller, symmetry related subparticles. The resulting high-resolution structure allowed us to build the MmuPV1 asymmetric unit for the first time and identify putative L2 density. We also used our program ISECC to quantify capsid flexibility, which revealed that capsomers move as rigid bodies connected by flexible linkers. The MmuPV1 flexibility was comparable to that of a HPV VLP previously characterized. The resulting MmuPV1 structure is a promising step forward in the study of papillomavirus and will provide a framework for continuing biochemical, genetic, and biophysical research for papillomaviruses

Patronin-mediated minus end growth is required for dendritic microtubule polarity.

Microtubule minus ends are thought to be stable in cells. Surprisingly, in Drosophila and zebrafish neurons, we observed persistent minus end growth, with runs lasting over 10 min. In Drosophila, extended minus end growth depended on Patronin, and Patronin reduction disrupted dendritic minus-end-out polarity. In fly dendrites, microtubule nucleation sites localize at dendrite branch points. Therefore, we hypothesized minus end growth might be particularly important beyond branch points. Distal dendrites have mixed polarity, and reduction of Patronin lowered the number of minus-end-out microtubules. More strikingly, extra Patronin made terminal dendrites almost completely minus-end-out, indicating low Patronin normally limits minus-end-out microtubules. To determine whether minus end growth populated new dendrites with microtubules, we analyzed dendrite development and regeneration. Minus ends extended into growing dendrites in the presence of Patronin. In sum, our data suggest that Patronin facilitates sustained microtubule minus end growth, which is critical for populating dendrites with minus-end-out microtubules

Bilaterian Giant Ankyrins Have a Common Evolutionary Origin and Play a Conserved Role in Patterning the Axon Initial Segment

<div><p>In vertebrate neurons, the axon initial segment (AIS) is specialized for action potential initiation. It is organized by a giant 480 Kd variant of ankyrin G (AnkG) that serves as an anchor for ion channels and is required for a plasma membrane diffusion barrier that excludes somatodendritic proteins from the axon. An unusually long exon required to encode this 480Kd variant is thought to have been inserted only recently during vertebrate evolution, so the giant ankyrin-based AIS scaffold has been viewed as a vertebrate adaptation for fast, precise signaling. We re-examined AIS evolution through phylogenomic analysis of ankyrins and by testing the role of ankyrins in proximal axon organization in a model multipolar <i>Drosophila</i> neuron (ddaE). We find giant isoforms of ankyrin in all major bilaterian phyla, and present evidence in favor of a single common origin for giant ankyrins and the corresponding long exon in a bilaterian ancestor. This finding raises the question of whether giant ankyrin isoforms play a conserved role in AIS organization throughout the Bilateria. We examined this possibility by looking for conserved ankyrin-dependent AIS features in <i>Drosophila</i> ddaE neurons via live imaging. We found that ddaE neurons have an axonal diffusion barrier proximal to the cell body that requires a giant isoform of the neuronal ankyrin Ank2. Furthermore, the potassium channel shal concentrates in the proximal axon in an Ank2-dependent manner. Our results indicate that the giant ankyrin-based cytoskeleton of the AIS may have evolved prior to the radiation of extant bilaterian lineages, much earlier than previously thought.</p></div

<i>Ciona intestinalis</i> ankyrin has a long exon comparable to mouse, fly and worm that can encode giant isoform(s).

<p>(A) A map of the Ciona intestinalis ankyrin locus showing the position of exons (color coded by domain) comprising an ankyrin ortholog gene prediction relative to the position of a giant ORF (red) that could represent a long exon. (B) <i>In situ</i> hybridization of mid (left) and late (right) tail bud stage larvae with a probe corresponding to an EST cluster from within the potential long exon (black box in A) shows expression in the sensory vesicle (SV) and the visceral ganglion (VG), which together comprise the bulk of the larval nervous system. Pictures are publically available from the Aniseed database (<b>A</b>scidian <b>N</b>etwork for <b>I</b>n <b>S</b>itu <b>E</b>xpression and <b>E</b>mbryological <b>D</b>ata; <a href="http://www.aniseed.cnrs.fr/" target="_blank">http://www.aniseed.cnrs.fr/</a>) where additional pictures and methods can be found (gene prediction KH.C1.943). (C) Comparison of the Ciona ankyrin long exon size with that of the average size of all ORFs (defined as > 300 nucleotides without a stop codon) in the Ciona genome draft. (D) Length distribution for the largest 1,000 ORFs in the Ciona genome in bins of 250 bp, reveals that the Ciona ankyrin long exons sits in the 2^nd largest ORF in the genome. (E-G) Similar length distribution graphs for the largest 1,000 ORFs in mouse, <i>Drosophila melanogaster</i> and <i>C</i>. <i>elegans</i> with the rank of long ankyring exons indicated.</p

Diffusion in the plasma membrane is restricted at the base of the axon compared to the base of the dendrite.

<p>A. Example images of dendrite and axon FRAP experiments at two different larval ages are shown. mCD8-RFP was expressed in class I dendritic arborization neurons. Bleaching was performed in the ddaE neuron either at the base of the comb-like dendrite or the base of the axon. The red circle indicates the bleach area. B. The average recovery of fluorescence into the bleach areas as shown in A is plotted on the graph; averages were calculated from 14 cells for the dendrite, 17 for axon 2 day and 13 for axon 3 day. Each cell was in a different animal. The error bars show the standard error of the mean. C. Bars show the recovery plateau (mean ± SEM) quantitated by averaging recovery values between 110 and 120 ms. The asterisk indicates significant difference (P < 0.01, t-test).</p

RNAi targeting Ank2L reduces the axonal diffusion barrier.

<p>A. mCD8-GFP was expressed in class I neurons, and proximal axons of ddaE neurons were photobleached. Example images of a control neuron are shown in the top row, and Ank2 RNAi neurons below. B. Quantitation of FRAP experiments in different genetic backgrounds is compiled in the graph. The average recovery is shown, with standard error shown as error bars. Number of cells tested for each genotype were: control-24, Ank2-19, Ank-12, CRMP-9. C. The recovery plateau (mean ± SEM) was quantitated by averaging recovery values between 110 and 120 ms. The asterisk indicates significant difference (p < 0.02, t-test).</p

Ankyrins are highly conserved between bilaterians, cnidarians and placozoans.

<p>(A) schematic diagram of a canonical ankyrin protein showing the 24 ankyrin repeats, the ZU5-ZU5-UPA cassette and the death domain (DD). The position of the long exon included in giant isoforms is shown for vertebrates (red star) and protostome invertebrates (green star). (B) Pairwise amino acid identity shared between mouse AnkG (Mmus_AnkG; Bilateria, deuterostome), <i>Drosophila melanogaster</i> Ank2 (Dmel_Ank2; Bilateria, protostome), <i>Nematostella vectensis</i> Ank (Nvec_Ank; Cnidaria) and <i>Trichoplax adhaerens</i> Ank (Tadh_Ank; Placozoa) for the shown alignment. (C) Amino acid alignment of core conserved domains is shown for bilaterian, cnidarian and placozoan ankyrins. Gene name is given at the left margin and amino acid position at the right margin. Residues identical in at least 3/4 sequences are shaded according to the domain color codes shown in (A). Domains boundaries are indicated with underlines; the 24 ankyrin repeats are underlined with alternating black and gray lines for clarity. The spectrin binding motif of vertebrate ankyrins is highlighted with a bright green outline.</p