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Expression of the glucose regulated protein GRP94 at the cell surface is required for myotube formation
No full textDistribution of conduction system fibers in the developing and adult rabbit heart revealed by an anti-neurofilament antibody.
No full textUsing an immunological approach, we demonstrated previously that a
neurofilament-like protein is expressed in rabbit heart conduction tissue
myocytes, and we proposed that these specialized cardiac muscle cells are of
neuroectodermal origin. In the present study, we used the expression of the
neurofilament-like protein as a marker for identifying conduction tissue cells
and studying their distribution in the developing heart. In 11-day-old rabbit
embryos, myocytes expressing the neurofilament-like protein were localized at the
atrioventricular and the sinoatrial junctions and had a ring-like distribution.
At embryonic day 12, reactive myocytes were found also in the subendocardial
layer of the dorsal ventricular wall, in continuity with labeled myocytes at the
atrioventricular junction. Examination of older embryos and of neonatal and adult
hearts revealed that the expression of the neurofilament-like protein was not
restricted to myocytes of conduction tissue regions, but it was also detectable
in myocytes of the sinoatrial ring bundle, in scattered myocytes localized in the
left sinal horn wall, and in the right atrium in proximity to atrioventricular
sulcus tissue. Thus, using an intracellular marker, we show that precursors of
adult atrial conduction tissue are distributed at the sinoatrial and
atrioventricular junctions; at variance, ventricular conduction tissue precursors
do not have a ring-like distribution but are localized in the subendocardial
layer, in continuity with the atrioventricular junctional myocytes
Transfection of skeletal myoblasts with antisense cDNA for GRP94 results in loss of fusion competence.
No full textCell-surface localization of the glucose-regulated protein GRP94 in skeletal myoblasts is involved in myotube formation
No full textMyotube formation requires cell surface expression of the glucose-regulated protein GRP94
No full text
Rabbit cardiac and skeletal myocytes differ in constitutive and inducible expression of the glucose-regulated protein GRP94.
Full text linkThe glucose-regulated protein GRP94 is a stress-inducible glycoprotein that is known to be constitutively and ubiquitously expressed in the endoplasmic reticulum of mammalian cells. From a rabbit heart cDNA library we isolated four overlapping clones coding for the rabbit homologue of GRP94 mRNA. Northern blot analysis shows that a 3200 nt mRNA species corresponding to GRP94 mRNA is detectable in several tissues and it is 5-fold more abundant in the heart than in the skeletal muscle. Hybridization analysis in situ shows that GRP94 mRNA accumulates in cardiac myocytes, whereas in skeletal muscles it is not detectable in myofibres. A monoclonal antibody raised by using a 35 kDa recombinant GRP94 polypeptide as immunogen detects a single reactive polypeptide of 94 kDa in a Western blot of liver and heart homogenates and does not react with skeletal muscle homogenates. Conversely, GRP94 mRNA and protein are detectable in both cardiac and skeletal muscle myocytes of fetal and neonatal rabbits. After 24 h of endotoxin administration to adult rabbits, GRP94 mRNA accumulation increases 3-fold in both heart and skeletal muscle and it is followed by a comparable increase in protein accumulation. However, hybridization and immunohistochemistry in situ do not reveal any change in the expression of GRP94 mRNA and protein in skeletal muscle myocytes after endotoxin treatment. Thus skeletal muscle fibres display a unique regulation of the GRP94 gene, which is upregulated during perinatal development, whereas in the adult animal it is apparently silent and not responsive to endotoxin treatment
Skeletal Muscle Atrophy Secondary to Simulated Microgravity is Counteracted by Curcumin-Induced Increase in Muscle Levels of the Stress-Protein Grp94.
No full textReduced amount of the glucose-regulated protein GRP94 in skeletal myoblasts results in loss of fusion competence
No full textWe previously showed that skeletal myocytes of the adult rabbit do not accumulate the endoplasmic reticulum glucose-regulated protein GRP94, neither constitutively nor inducibly, at variance with skeletal myocytes during perinatal development (5), Here we show that C2C12 cells upregulate GRP94 during differentiation and, similarly to primary cultures of murine skeletal myocytes, specifically display GRP94 immunoreactivity on the cell surface. Stable transfection of C2C12 cells with grp94 antisense cDNA shows lack of myotube formation in clones displaying >40% reduction in GRP94 amount. The same result is obtained after irt vivo injection of grp94-antisense myoblasts, Conversely, GRP94 overexpression is accompanied by accelerated myotube formation. Analyses of BrdU incorporation, p21 nuclear translocation, and muscle-gene expression show that muscle differentiation is not apparently affected in grp94-antisense clones. In contrast, cell-surface GRP94 is greatly reduced in grp94-antisense clones, as shown by immunocytochemistry and precipitation of cell-surface biotinylated proteins. Thus, cell-surface expression of GRP94 is necessary for maintenance of fusion competence. Furthermore, differentiating C2C12 cells grown in the presence of anti-GRP94 antibody show decreased myotube number suggesting that cell-surface GRP94 is directly involved in myoblast fusion process
Heart conduction system: a neural crest derivative?
No full textUsing the anti-neurofilament monoclonal antibody iC8 we report here that muscle
fibers of the conduction system of the adult and developing rabbit heart express
a cytoskeletal protein antigenically and electrophoretically similar to the
middle subunit of neurofilaments (NF-M). In the 11-day embryo a number of cardiac
muscle cells also express a neural crest surface marker recognized by the
monoclonal antibody HNK-1. Both markers are found in many cells of the 3rd and
4th branchial arches, which are populated by cells of neural crest origin. In the
11-day embryo cells of the 4th branchial arch are in close proximity to and
intermingled with the atrial myocardium: cells co-expressing sarcomeric myosin
heavy chain with iC8 and HNK-1 immunoreactivity are seen at these sites. The
findings suggest that conduction tissue cells of the rabbit heart originate from
a population of neural crest-derived cells migrating from the branchial arches
into the developing heart
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