Regulation of the dystrophin-associated glycoprotein complex composition by the metabolic properties of muscle fibres

The dystrophin-glycoprotein complex (DGC) links the muscle cytoskeleton to the extracellular matrix and is responsible for force transduction and protects the muscle fibres from contraction induced damage. Mutations in components of the DGC are responsible for muscular dystrophies and congenital myopathies. Expression of DGC components have been shown to be altered in many myopathies. In contrast we have very little evidence of whether adaptive changes in muscle impact on DGC expression. In this study we investigated connection between muscle fibre phenotype and the DGC. Our study reveals that the levels of DGC proteins at the sarcolemma differ in highly glycolytic muscle compared to wild-type and that these changes can be normalised by the super-imposition of an oxidative metabolic programme. Importantly we show that the metabolic properties of the muscle do not impact on the total amount of DGC components at the protein level. Our work shows that the metabolic property of a muscle fibre is a key factor in regulating the expression of DGC proteins at the sarcolemma

Hes5 Expression in the Postnatal and Adult Mouse Inner Ear and the Drug-Damaged Cochlea

The Notch signaling pathway is known to have multiple roles during development of the inner ear. Notch signaling activates transcription of Hes5, a homologue of Drosophila hairy and enhancer of split, which encodes a basic helix-loop-helix transcriptional repressor. Previous studies have shown that Hes5 is expressed in the cochlea during embryonic development, and loss of Hes5 leads to overproduction of auditory and vestibular hair cells. However, due to technical limitations and inconsistency between previous reports, the precise spatial and temporal pattern of Hes5 expression in the postnatal and adult inner ear has remained unclear. In this study, we use Hes5-GFP transgenic mice and in situ hybridization to report the expression pattern of Hes5 in the inner ear. We find that Hes5 is expressed in the developing auditory epithelium of the cochlea beginning at embryonic day 14.5 (E14.5), becomes restricted to a particular subset of cochlear supporting cells, is downregulated in the postnatal cochlea, and is not present in adults. In the vestibular system, we detect Hes5 in developing supporting cells as early as E12.5 and find that Hes5 expression is maintained in some adult vestibular supporting cells. In order to determine the effect of hair cell damage on Notch signaling in the cochlea, we damaged cochlear hair cells of adult Hes5-GFP mice in vivo using injection of kanamycin and furosemide. Although outer hair cells were killed in treated animals and supporting cells were still present after damage, supporting cells did not upregulate Hes5-GFP in the damaged cochlea. Therefore, absence of Notch-Hes5 signaling in the normal and damaged adult cochlea is correlated with lack of regeneration potential, while its presence in the neonatal cochlea and adult vestibular epithelia is associated with greater capacity for plasticity or regeneration in these tissues; which suggests that this pathway may be involved in regulating regenerative potential

Variation in content and function of non-neuronal cells in the outgrowth of sympathetic ganglia from embryos of differing age

Studies on cellular interactions in the developing nervous system are greatly facilitated by the availability of tissue culture preparations that contain single or combined populations of neurons and non-neuronal cells (NNCs). Using superior cervical ganglia (SCG) from early E15 rats on air-dried collagen, we were able to prepare cultures containing neurons along with Schwann cells (SCs) as the only NNC type present without the use of antimitotic treatment and cultures containing only neurons, following brief antimitotic treatment. Light-microscopic observation of E15 outgrowth showed a uniform population of flattened cells, unlike that of E20 cultures, which contained a mixture of spindle-shaped and flattened cells. Autoradiograms following [3H]thymidine administration to E15 cultures revealed a striking gradient of nuclear labeling: Only a few cells were labeled near the explant and nearly all cells were labeled at the growth front. This was in marked contrast to E20 cultures, in which nuclei were labeled throughout the outgrowth. The conclusion that the labeling gradient is explained by the presence of SCs without other NNC types in E15 cultures was confirmed by immunocytochemical studies. Anti-laminin antibodies stain only those extracellular matrix components related to the SC surface, whereas anti-fibronectin antibodies stain fibroblast- related components (Cornbrooks et al., 1983a). Anti-laminin antibodies stained cell surfaces in both E15 and E20 outgrowth. E15 outgrowth did not stain with anti-fibronectin antibodies although marked staining was obtained in E20 cultures. Electron microscopy confirmed the presence of only SCs in E15, and of both SCs and fibroblasts in E20 outgrowth. Thus, it appears that there is a narrow developmental window in which the ganglia contain neurons and SCs but relatively few fibroblast components; cultures prepared from ganglia at this stage form outgrowth containing only neurites and SCs without antimitotic treatment. Surprisingly, neither SC ensheathment nor SC basal lamina formation was normal in E15 and E20 outgrowth. When either E15 or E20 SCG SCs were transplanted onto dorsal root ganglion neurons free of endogenous SCs, however, the sensory neurites were typically ensheathed or myelinated and basal lamina appeared 9 d later, identifying the SCG NNCs as functionally competent SCs

Chemical neuroanatomy of the hypothalamo-hypophyseal system in sturgeons

International audienceThe preoptic-hypothalamo-hypophyseal system of sturgeons, located at the base of the brain, has a neurosecretory role exerted by hypophysiotropic neurons most of them located in the preoptic and hypothalamic periventricular region. The majority of those cells are of the cerebrospinal fluid-contacting type and exhibit short processes reaching the ventricular lumen. Moreover, the processes of those hypophysiotropic neurons course along the hypothalamic floor toward the hypophysis forming a preoptic-hypothalamo-hypophyseal tract. This chapter summarizes available data on the distribution of several hypophysiotropic factors, such as galanin, neurophysin, somatostatin, or gonadotropin-releasing hormone, in the preoptic-hypothalamo-hypophyseal system of sturgeons obtained by the use of immunohistochemical techniques. Immunoreactive neurons to those substances were found in the preoptic and hypothalamic nuclei, and immunoreactive fibers were observed along the preoptic-hypothalamo-hypophyseal tract and in the hypophysis, indicating their hypophysiotrophic role in the brain of sturgeons. Thus, most of the neuropeptides and neurohormones found in tetrapods are also present in sturgeons, suggesting that their common ancestors already possessed such regulatory systems. Unfortunately, because of the difficulty in approaching the physiology of sturgeons (size, cost, etc.), the number of experimental studies aiming at deciphering the roles of such neuropeptides and neurohormones is very limited, although we can speculate that part of the functions supported by these neurohormones would be similar. © Springer International Publishing AG, part of Springer Nature 2018. All rights reserved