Deltamethrin resistance in the salmon louse, Lepeophtheirus salmonis (Krøyer): Maternal inheritance and reduced apoptosis

publishedVersio

Myonuclear content regulates cell size with similar scaling properties in mice and humans

Muscle fibers are the largest cells in the body, and one of its few syncytia. Individual cell sizes are variable and adaptable, but what governs cell size has been unclear. We find that muscle fibers are DNA scarce compared to other cells, and that the nuclear number (N) adheres to the relationship N = aVb where V is the cytoplasmic volume. N invariably scales sublinearly to V (b < 1), making larger cells even more DNA scarce. N scales linearly to cell surface in adult humans, in adult and developing mice, and in mice with genetically reduced N, but in the latter the relationship eventually fails when they reach adulthood with extremely large myonuclear domains. Another exception is denervation-atrophy where nuclei are not eliminated. In conclusion, scaling exponents are remarkably similar across species, developmental stages and experimental conditions, suggesting an underlying scaling law where DNA-content functions as a limiter of muscle cell size.publishedVersio

Enhanced exercise and regenerative capacity in a mouse model that violates size constraints of oxidative muscle fibres

A central tenet of skeletal muscle biology is the existence of an inverse relationship between the oxidative fibre capacity and its size. However, robustness of this relationship is unknown. We show that superimposition of Estrogen-related receptor gamma (Erry) on the myostatin (Mtn) mouse null background (Mtn(-/-)Err gamma(Tg/+)) results in hypertrophic muscle with a high oxidative capacity thus violating the inverse relationship between fibre size and oxidative capacity. We also examined the canonical view that oxidative muscle phenotype positively correlate with Satellite cell number, the resident stem cells of skeletal muscle. Surprisingly, hypertrophic fibres from Mtn(-/-)Err gamma(Tg/+) mouse showed satellite cell deficit which unexpectedly did not affect muscle regeneration. These observations 1) challenge the concept of a constraint between fibre size and oxidative capacity and 2) indicate the important role of the microcirculation in the regenerative capacity of a muscle even when satellite cell numbers are reduced.Peer reviewe

Overexpression of SMPX in adult skeletal muscle does not change skeletal muscle fiber type or size

Mechanical factors such as stretch are thought to be important in the regulation of muscle phenotype. Small muscle protein X-linked (SMPX) is upregulated by stretch in skeletal muscle and has been suggested to serve both as a transcription factor and a mechanosensor, possibly giving rise to changes in both fiber size and fiber type. We have used in vivo confocal imaging to study the subcellular localization of SMPX in skeletal muscle fibers of adult rats using a SMPX-EGFP fusion protein. The fusion protein was localized predominantly in repetitive double stripes flanking the Z-disc, and was excluded from all nuclei. This localization would be consistent with SMPX being a mechanoreceptor, but not with SMPX playing a role as a transcription factor. In vivo overexpression of ectopic SMPX in skeletal muscle of adult mice gave no significant changes in fiber type distribution or cross sectional area, thus a role of SMPX in regulating muscle phenotype remains unclear

DNA vaccines: MHC II-targeted vaccine protein produced by transfected muscle fibres induces a local inflammatory cell infiltrate in mice

Vaccination with naked DNA holds great promise but immunogenicity needs to be improved. DNA constructs encoding bivalent proteins that bind antigen-presenting cells (APC) for delivery of antigen have been shown to enhance T and B cell responses and protection in tumour challenge experiments. However, the mechanism for the increased potency remains to be determined. Here we have constructed DNA vaccines that express the fluorescent protein mCherry, a strategy which allowed tracking of vaccine proteins. Transfected muscle fibres in mice were visualized, and their relationship to infiltrating mononuclear cells could be determined. Interestingly, muscle fibers that produced MHC class II-specific dimeric vaccine proteins with mCherry were for weeks surrounded by a localized intense cellular infiltrate composed of CD45+, MHC class II+ and CD11b+ cells. Increasing numbers of eosinophils were observed among the infiltrating cells from day 7 after immunization. The local infiltrate surrounding mCherry+ muscle fibers was dependent on the MHC II-specificity of the vaccine proteins since the control, a non-targeted vaccine protein, failed to induce similar infiltrates. Chemokines measured on day 3 in immunized muscle indicate both a DNA effect and an electroporation effect. No influence of targeting was observed. These results contribute to our understanding for why targeted DNA vaccines have an improved immunogenicity

Specific labelling of myonuclei by an antibody against Pericentriolar material 1 (PCM1) on skeletal muscle tissue sections

Aim: Skeletal muscle is a heterogeneous tissue containing several different cell types, and only about 40%‐50% of the cell nuclei within the tissue belong to myofibres. Existing technology, attempting to distinguish myonuclei from other nuclei at the light microscopy level, has led to controversies in our understanding of the basic cell biology of muscle plasticity. This study aims at demonstrating that an antibody against the protein pericentriolar material 1 (PCM1) can be used to reliably identify myonuclei on histological cross sections from humans, mice and rats. Methods: Cryosections were labelled with a polyclonal antibody against PCM1. The specificity of the labelling for myonuclei was verified using 3D reconstructions of confocal z‐stacks triple‐labelled for DNA, dystrophin and PCM1, and by co‐localization with nuclear mCherry driven by the muscle‐specific Alpha‐Actin‐1 promoter after viral transduction. Results: The PCM1 antibody specifically labelled all myonuclei, and myonuclei only, in cryosections of muscles from rats, mice and men. Nuclei in other cell types including satellite cells were not labelled. Both normal muscles and hypertrophic muscles after synergist ablation were investigated. Conclusion: Pericentriolar material 1 can be used as a specific histological marker for myonuclei in skeletal muscle tissue without relying on counterstaining of other structures or cumbersome and subjective analysis of nuclear positioning

SMPX-EGFP was localized in bands flanking the z-disc.

<p>A) <i>In situ</i> confocal image of EGFP or SMPX-EGFP expression from an isolated EDL rat muscle in Ringer-solution. Scale bar is 10 microns. B) <i>In vitro</i> confocal image of EGFP or SMPX-EGFP stained with Alexa Fluor 680 Phalloidin (red) to visualize actin filaments. Scale bar is 10 microns (inset 1 micron).</p

SMPX-EGFP was excluded from all myonuclei.

<p>A) C2C12 myoblasts expressing either EGFP or SMPX-EGFP stained with Hoechst 33342 to visualize nuclei. B) <i>In vitro</i> confocal image of dissected single rat EDL muscle fibers expressing EGFP or SMPX-EGFP stained with DAPI to visualize nuclei. C) Confocal images of EDL muscle fibers <i>in situ,</i> after no treatment (CON) or functional overload for 18 hours (LOAD), expressing SMPX-EGFP stained with Hoechst 33342 to visualize nuclei. Myonuclei are labeled with arrowheads. Scale bar is 10 microns.</p

Expression of SMPX plasmids, in vitro and in vivo.

<p>A) Western blot of SMPX-EGFP expression in HEK-293 cells stained with antibodies against EGFP. Lane 1: Negative control. Lane 2: EGFP only. Lane 3-6: SMPX-EGFP. B) <i>In vivo</i> fluorescence image of EDL muscle expressing pCMS-EGFP-<i>Smpx</i>. Scalebar is 500 microns. Inset: High magnification of single fibers. Scalebar is 50 microns. C) β-gal (left) and myosin heavy chain type 2A (right) stain on neighboring cross-sections from the same muscle as in B). β-gal expressing fibers marked with asterisks. Scale bar is 50 microns.</p

Muscle fiber type and cross sectional area (CSA) in mouse EDL.

<p>Single fibers from muscles transfected with either pCMS-EGFP (left leg sham control, only expressing EGFP) or pCMS-EGFP-<i>Smpx</i> (expressing SMPX and EGFP). A) CSA with n = 226/254 cells for sham/SMPX. Values are means +/- SD. B) Fiber type composition of the same fibers as in A.</p