Sequential expression during postnatal development of specific markers of junctional and free sarcoplasmic reticulum in chicken pectoralis muscle

Structural Adaptation of the Excitation-Contraction Coupling Apparatus in Calsequestrin1-Null Mice during Postnatal Development

The precise arrangement and peculiar interaction of transverse tubule (T-tubule) and sarcoplasmic reticulum (SR) membranes efficiently guarantee adequate contractile properties of skeletal muscle fibers. Fast muscle fibers from mice lacking calsequestrin 1 (CASQ1) are characterized by the profound ultrastructural remodeling of T-tubule/SR junctions. This study investigates the role of CASQ1, an essential component of calcium release units (CRUs), in the postnatal development of muscle fibers. By using CASQ1-knockout mice, we examined the maturation of CRUs and the involvement of different junctional proteins in the juxtaposition of the membrane system. Our morphological investigation of both wild-type (WT) and CASQ1-null extensor digitorum longus (EDL) fibers, from 1 week to 4 months of age, yielded noteworthy findings. Firstly, we observed that the absence of CASQ1 hindered the full maturation of CRUs, despite the correct localization of key junctional components (ryanodine receptor, dihydropyridine receptor, and triadin) to the junctional SR in adult animals. Furthermore, analysis of protein expression profiles related to T-tubule biogenesis and organization (junctophilin 1, amphiphysin 2, caveolin 3, and mitsugumin 29) demonstrated delayed progression in their expression during postnatal development in the absence of CASQ1, suggesting the impaired maturation of CRUs. The absence of CASQ1 directly impacts the proper assembly of CRUs during development and influences the expression and coordination of other proteins involved in T-tubule biogenesis and organization.

Effect of feed restriction timing on live performance, breast myopathy occurrence, and muscle fiber degeneration in 2 broiler chicken genetic lines

During recent years, research on meat quality in poultry has aimed to evaluate the presence and consequences of breast myopathies as well as the factors which can affect their occurrence by modifying the growth rate. A total of 900 broiler chickens were reared until slaughter (48 D) to evaluate the effect of 2 genetic lines (A vs. B) and feeding plans (ad libitum [AL], early restricted [ER], from 13 to 23 D of age, and late restricted [LR], from 27 to 37 D of age; restriction rate: 80%) on performance, meat quality, and breast muscle myopathies. Calsequestrin and vascular endothelial growth factor (VEGF) expressions, and muscle fiber degeneration (MFD) were recorded at 22, 36, and 48 D. Chickens in the AL treatment had greater final live (P < 0.01) and carcass weights and proportion of pectoralis major muscle (P = 0.04) compared to chickens in the LR treatment, whereas chickens in the ER treatment had intermediate final live (3,454 g) and carcass weights, and proportion of pectoralis major muscle (25.6%). Chickens of line A were heavier than chickens of line B (P < 0.001), and had a greater feed conversion rate. Chickens of line A also had a greater dressing out percentage (P < 0.001), but a lower proportion of pectoralis major muscle (P = 0.04), as well as a greater meat pH (P < 0.001), meat cooking losses (P < 0.01), and shear force of the pectoralis major muscle (P = 0.03). Calsequestrin and VEGF mRNA were significantly lower in ER and LR chickens compared to AL chickens after feed restriction and during refeeding (P < 0.05). MFD scores increased with chicken age (P < 0.001) and differed between genetic lines (P < 0.001). Neither feeding plan nor genetic line affected the occurrence of white striping or wooden breast condition.

Histidine-rich calcium binding protein: the new regulator of sarcoplasmic reticulum calcium cycling

The histidine-rich calcium binding protein (HRC) is a novel regulator of sarcoplasmic reticulum (SR) Ca(2+)-uptake, storage and release. Residing in the SR lumen, HRC binds Ca(2+) with high capacity but low affinity. In vitro phosphorylation of HRC affects ryanodine affinity of the ryanodine receptor (RyR), suggesting a functional role of HRC on SR Ca(2+)-release. Indeed, acute HRC overexpression in isolated rodent cardiomyocytes decreases Ca(2+)-induced Ca(2+)-release, increases SR Ca(2+)-load, and impairs contractility. The HRC effects on RyR may be regulated by the Ca(2+)-sensitivity of its interaction with triadin. However, HRC also affects the SR Ca(2+)-ATPase, as shown by HRC overexpression in transgenic mouse hearts, which resulted in reduced SR Ca(2+)-uptake rates, cardiac remodeling and hypertrophy. In fact, in vitro generated evidence suggests that HRC directly interacts with SR Ca(2+)-ATPase2, supporting a dual role of HRC in Ca(2+)-homeostasis: regulation of both SR Ca(2+)-uptake and Ca(2+)-release. Furthermore, HRC plays an important role in myocyte differentiation and in antiapoptotic cardioprotection against ischemia/reperfusion induced cardiac injury. Interestingly, HRC has been linked with familiar cardiac conduction disease and an HRC polymorphism was shown to associate with malignant ventricular arrhythmias in the background of idiopathic dilated cardiomyopathy. This review summarizes studies, which have established the critical role of HRC in Ca(2+)-homeostasis, suggesting its importance in cardiac physiology and pathophysiology.

Subcellular localization of S100A11 (S100C, calgizzarin) in developing and adult avian skeletal muscles

S100A11 is a member of a multigenic family of Ca(2+)-modulated proteins of the EF-hand type. We studied the subcellular localization of S100A11 in developing and adult avian skeletal muscle cells by confocal laser scanning microscopy and immunogold cytochemistry to get information about possible functional roles of this protein. Analyses of alpha-actinin, S100A1 and S100B were done in parallel for comparison. Low levels of S100A11 were found in skeletal muscle cells at embryonic day (E) 8. At E12, S100A11 was found in myotubes in the form of fine dots located between Z-discs, and on the sarcolemma and its invaginations. At E15, S100A11 was found on the sarcolemma and internal membranes, likely longitudinal tubules, where the protein was co-localized in part with S100A1 and S100B. At E18 and afterwards, co-localization of the three S100 proteins on internal membranes was almost complete. No evidence for association of S100A11 with the contractile elements of the sarcomeres was obtained. Our data suggests that, like S100A1 and S100B, S100A11 might have a role in the regulation of membrane activities, probably in relation to Ca(2+) fluxes in skeletal muscle cells.

Annexin V, annexin VI, S100A1 and S100B in developing and adult avian skeletal muscles

Annexins and S100 proteins constitute two multigenic families of Ca2+-modulated proteins that have been implicated in the regulation of both intracellular and extracellular activities. Some annexins can interact with certain S100 protein dimers thereby forming heterotetramers in which an S100 dimer crosslinks two copies of the partner annexin. It is suggested that S100 protein binding to an annexin might serve the function of regulating annexin function and annexin binding to an S100 protein might regulate S100 function. In the present study, annexin V, annexin VI (or ANXA5 and ANXA6, respectively, according to a novel nomenclature), S100A1 and S100B were analyzed for their subcellular localization in developing and adult avian skeletal muscles by confocal laser scanning microscopy, immunogold cytochemistry, and western blotting, and for their ability to form annexin-S100 heterocomplex in vivo by immunoprecipitation. These four proteins displayed distinct expression patterns, ANXA5 being the first to be expressed in myotubes (i.e. at embryonic day 8), followed by ANXA6 (at embryonic day 12) and S100A1 and S100B (between embryonic day 12 and embryonic day 15). The two annexins and the two S100 proteins were found associated to different extents with the sarcolemma, membranes of the sarcoplasmic reticulum, and putative transverse tubules where they appeared to be co-localized from embryonic day 18 onwards. No one of these proteins was found associated with the contractile apparatus of the sarcomeres. Immunoprecipitation studies indicated that ANXA6/S100A1 and ANXA6/S100B complexes formed in vivo. Whereas, ANXA5 was not recovered in S100A1 or S100B immunoprecipitates. From our data we suggest that: (i) ANXA5 and ANXA6, and S100A1 and S100B can be used as markers of skeletal muscle development; (ii) ANXA6 and S100A1 and S100B appear strategically located close to or on skeletal muscle membrane organelles that are critically involved in the regulation of Ca2+ fluxes, thus supporting previous in vitro observations implicating S100A1 and ANXA6 in the stimulation of Ca2+-induced Ca2+ release; and (iii) ANXA6/S100A1 and ANXA6/S100B complexes can form in vivo thereby regulating each other activities and/or acting in concert to regulate membrane-associated activities.

Ca(2+)-dependent interaction of triadin with histidine-rich Ca(2+)-binding protein carboxyl-terminal region

A direct binding of HRC (histidine-rich Ca(2+)-binding protein) to triadin, the main transmembrane protein of the junctional sarcoplasmic reticulum (SR) of skeletal muscle, seems well supported. Opinions are still divided, however, concerning the triadin domain involved, either the cytoplasmic or the lumenal domain, and the exact role played by Ca(2+), in the protein-to-protein interaction. Further support for colocalization of HRC with triadin cytoplasmic domain is provided here by experiments of mild tryptic digestion of tightly sealed TC vesicles. Accordingly, we show that HRC is preferentially phosphorylated by endogenous CaM K II, anchored to SR membrane on the cytoplasmic side, and not by lumenally located casein kinase 2. We demonstrate that HRC can be isolated as a complex with triadin, following equilibrium sucrose-density centrifugation in the presence of mM Ca(2+). Here, we characterized the COOH-terminal portion of rabbit HRC, expressed and purified as a fusion protein (HRC(569-852)), with respect to Ca(2+)-binding properties, and to the interaction with triadin on blots, as a function of the concentration of Ca(2+). Our results identify the polyglutamic stretch near the COOH terminus, as the Ca(2+)-binding site responsible, both for the acceleration in mobility of HRC on SDS-PAGE in the presence of millimolar concentrations of Ca(2+), and for the enhancement by high Ca(2+) of the interaction between HRC and triadin cytoplasmic segment. (c)2001 Elsevier Science.

Interaction of triadin with histidine-rich Ca(2+)-binding protein at the triadic junction in skeletal muscle fibers

The present study documents the binding interaction of skeletal muscle sarcoplasmic reticulum (SR) transmembrane protein triadin with peripheral histidine-rich, Ca(2+)-binding protein (HCP). In addition to providing further evidence that HCP coenriches with RyR1, FKBP-12, triadin and calsequestrin (CS) in sucrose-density-purified TC vesicles, using specific polyclonal antibody, we show it to be expressed as a single protein species, both in fast-twitch and slow-twitch fibers, and to identically localize to the I-band. Colocalization of HCP and triadin at junctional triads is supported by the overlapping staining pattern using monoclonal antibodies to triadin. We show a specific binding interaction between digoxigenin-HCP and triadin, using ligand blot techniques. The importance of this finding is strengthened by the similarities in binding affinity and in Ca2+ dependence, (0.1-1 mM Ca2+) of the interaction of digoxigenin-HCP with immobilized TC vesicles. Suggesting that triadin dually interacts with HCP and with CS, at distinct sites, we have found that triadin-CS interaction in overlays does not require the presence of Ca2+. Consistent with the binding of CS to triadin luminal domain (Guo and Campbell, 1995), we show that binding sites for digoxigenin-CS, although not binding sites for digoxigenin-HCP, can be recovered in the 92 kDa triadin fragment, after chymotryptic cleavage of the NH2-terminal end of the folded molecule in intact TC vesicles. These differential effects form the basis for the hypothesis that HCP anchors to the junctional membrane domain of the SR, through binding to triadin short cytoplasmic domain at the NH2 terminus. Although the function of this interaction, as such, is not well understood, it seems of potential biological interest within the more general context of the structural-functional role of triadin at the triadic junction in skeletal muscle.

Interaction of triadin with histidine-rich Ca(2+)-binding protein at the triadic junction in skeletal muscle fibers

The present study documents the binding interaction of skeletal muscle sarcoplasmic reticulum (SR) transmembrane protein triadin with peripheral histidine-rich, Ca(2+)-binding protein (HCP). In addition to providing further evidence that HCP coenriches with RyR1, FKBP-12, triadin and calsequestrin (CS) in sucrose-density-purified TC vesicles, using specific polyclonal antibody, we show it to be expressed as a single protein species, both in fast-twitch and slow-twitch fibers, and to identically localize to the I-band. Colocalization of HCP and triadin at junctional triads is supported by the overlapping staining pattern using monoclonal antibodies to triadin. We show a specific binding interaction between digoxigenin-HCP and triadin, using ligand blot techniques. The importance of this finding is strengthened by the similarities in binding affinity and in Ca2+ dependence, (0.1-1 mM Ca2+) of the interaction of digoxigenin-HCP with immobilized TC vesicles. Suggesting that triadin dually interacts with HCP and with CS, at distinct sites, we have found that triadin-CS interaction in overlays does not require the presence of Ca2+. Consistent with the binding of CS to triadin luminal domain (Guo and Campbell, 1995), we show that binding sites for digoxigenin-CS, although not binding sites for digoxigenin-HCP, can be recovered in the 92 kDa triadin fragment, after chymotryptic cleavage of the NH2-terminal end of the folded molecule in intact TC vesicles. These differential effects form the basis for the hypothesis that HCP anchors to the junctional membrane domain of the SR, through binding to triadin short cytoplasmic domain at the NH2 terminus. Although the function of this interaction, as such, is not well understood, it seems of potential biological interest within the more general context of the structural-functional role of triadin at the triadic junction in skeletal muscle.

Differential response of the membrane systems involved in excitation-contraction coupling to early and later postnatal denervation in rat skeletal muscle

We compared the morphological features of the membrane systems involved in excitation-contraction (E-C) coupling during early postnatal development stages in rat skeletal muscles (tibialis anterior) denervated either at birth or 7 days after birth. Four obvious structural changes are observed in the arrangement of the transverse (T) tubule network and the disposition of triads following early postnatal denervation: (1) an increase in the longitudinal segments of the T tubule network, (2) changes in the direction and disposition of triads, (3) the appearance of caveolae clusters, (4) the appearance of pentads and heptads (i.e. a close apposition of two or three T tubule elements with three or four elements of terminal cisternae of sarcoplasmic reticulum). The increased presence of longitudinal T tubules parallels the loss of cross striations, and this in turn is due to misalignment of the myofibrils. The clusters of caveolae appear almost exclusively in muscle fibres denervated at birth, and pentads and heptads are more frequently observed in muscles denervated at 7 days. The differential growth of muscle fibres in response to denervation leads to the formation of abnormal membrane systems involved in the E-C coupling with very unique morphological features, which differ from the case of denervation in adult muscle fibres.

Colocalization of the dihydropyridine receptor, the plasma-membrane calcium ATPase isoform 1 and the sodium/calcium exchanger to the junctional-membrane domain of transverse tubules of rabbit skeletal muscle

The subcellular distribution of the calmodulin-stimulated plasma-membrane Ca(2+)-ATPase (PMCA) has been studied in rat and rabbit skeletal muscle cells by indirect (calmodulin gel overlays) and direct (Western blotting with specific antibodies) methods. It has also been studied in situ in immunocytochemistry experiments. The distribution of PMCA has been compared with that of the NA+/Ca2+ exchanger and of the dihydropyridine receptor, which has been studied by Western blotting with specific antibodies. Both PMCA and the Na+/Ca2+ exchanger had a dual localization, i.e., they were found in the plasma membrane and in the transverse-tubule fractions of the two main types of skeletal muscles studied. The pump and the exchanger were not diffusely distributed in the transverse-tubule-membrane system, but specifically confined to the membrane domain where the dihydropyridine receptor was also localized, i.e., the junctional membrane. Experiments with isoform-specific antibodies have shown that the pump isoform expressed in skeletal muscle is PMCA 1.

Expression of sarcoplasmic reticulum Ca2+ transport proteins in cold-acclimating ducklings

The relationship between the cold-induced increase in sarcoplasmic reticulum (SR) Ca2+ transport proteins and the development of muscular nonshivering theermogenesis (NST) was investigated by determining the time course of expression of the sarcoplasmic or endoplasmic reticulum Ca(2+)-ATPase (SERCA), Ca2+ release channel, and calsequestrin in control and cold-acclimating ducklings. 45Ca2+ uptake and [3H]ryanodine binding measurements with skeletal muscle homogenates showed that a cold acclimation period of approximately 4 wk was required to observe a substantial increase in Ca(2+)-ATPase activity and Ca2+ release channel content, which correlates well with NST development Immunoblot analysis of muscle homogenates showed no differences in calsequestrin levels but revealed that the decrease in SERCA2a content was delayed in cold-acclimating birds and that the SERCA1 level was increased after 4 wk of cold acclimation. The persistence of SERCA2a may be related to shivering thermogenesis occurring preferentially in slow-twitch fibers. SERCA1 may account for most of the cold-induced increase in 45Ca2+ uptake activity, suggesting the preferential occurrence of a Ca(2+)-dependent NST in fast-twitch fibers.

Perinatal changes in avian muscle: implications from ultrastructure for the development of endothermy

Endothermic heat production and the capacity to shiver develop soon after hatching in birds, permitting chicks to regulate their body temperature. Physiological studies have not clearly identified the developmental events causing this change in function. Here, we use electron microscopy to examine the development of structures involved in muscle activation, contraction, and metabolism coincident with the development of shivering thermogenesis. A stereological study was used to compare the ultrastructure of chicken iliofibularis before endothermic heat production was present (24 h before hatching) and 120 h later, when the iliofibularis had substantial capacity for shivering. Profound increases were found in the t-tubule system and terminal cisternae, mitochondrial cristae, and lipids. The number of triadic profiles increased 3.8-fold (7.6 +/- 1.31/100 microns 2 to 28.5 +/- 2.90/100 microns 2 fiber area). The surface area of cristae per mitochondrial volume doubled (12.0 +/- 1.50 microns 2/microns 3 to 25.7 +/- 1.84 microns 2/microns 3). Lipid droplets were rare in the iliofibularis of embryos about to hatch, but accounted for 4.4% of the muscle fiber volume in day 4 birds. We suggest that these ultrastructural changes more fully activate the iliofibularis, allow it to produce more heat both from calcium pumping and from contraction, and increase its endurance, thus permitting the muscle to be effective in thermogenesis.

Characterization study of the ryanodine receptor and of calsequestrin isoforms of mammalian skeletal muscles in relation to fibre types

We have investigated high-affinity ryanodine-binding sites in membrane preparations from representative fast-twitch and slow-twitch muscles of the rabbit and rat, as well as from human mixed muscle. Our results, obtained in high-ionic strength binding buffer, demonstrate extensive similarities in binding affinity for [3H]ryanodine (Kd: about 10 nM) and a two-fold to four-fold difference in membrane density of the ryanodine receptor between fast-twitch and slow-twitch muscle of the rat and rabbit, respectively. The [3H]ryanodine-pCa relationship for the Ca(2+)-activation curve of ryanodine binding was found to be similar for all mammalian muscles, as tested at 20 nM ryanodine. With 10 mM caffeine or 50 microM doxorubicin the pCa for half-maximal activation of [3H]ryanodine binding invariably shifted from an average pCa value of 6.5 to pCa 7.1-7.3. IC50 values for the inhibition of [3H]ryanodine binding by Ruthenium Red, a Ca(2+)-release channel blocker, did not differ significantly (range 0.3-1.0 microM). The Ca(2+)-dependence curve (range 1 nM-10 mM free Ca2+) that we have observed at 5 nM ryanodine, for [3H]ryanodine binding to terminal cisternae from rabbit fast-twitch, as well as slow-twitch muscle, is bell-shaped and differs from that obtained with cardiac terminal cisternae from the same species. Cardiac ryanodine receptor is also clearly distinguishable for electrophoretic mobility, Cleveland's peptide maps, and, most strikingly, for total lack of cross-reactivity with polyclonal antibody to fast skeletal RyR. By the same properties, the ryanodine receptor of fast- and slow-twitch muscle appear to be the same or a similar protein. On investigating the composition of calsequestrin in rat and human skeletal muscles, both in membrane-bound form and after purification by phenyl-Sepharose chromatography, we have been able to show that, independent of the animal species, the cardiac isoform, as characterized by the identical amino-terminal amino-acid sequence, pattern of immunoreactivity, and lack of Ca(2+)-dependent shift in mobility on SDS-PAGE, is exclusively expressed in slow-twitch fibres, together with the main fast-skeletal calsequestrin isoform. While our experimental findings strongly argue for the presence of only one population of skeletal-specific Ca(2+)-release channels in junctional terminal cisternae of mammalian fast-twitch and slow-twitch muscle, they at the same time suggest the existence of differences in calsequestrin modulation of Ca(2+)-release, depending on its isoform composition.

Development of the excitation-contraction coupling apparatus in skeletal muscle: peripheral and internal calcium release units are formed sequentially

The development of calcium release units and of transverse tubules has been studied in skeletal muscle fibres from embryonal and newborn chicken. Three constituents of calcium release units: the tetrads, the feet and an internal protein directly associated with junctional surface of the sarcoplasmic reticulum are visualized by various electron microscope techniques. Evidence in the literature indicates that the three components correspond to the voltage sensors, the sarcoplasmic reticulum calcium release channels and the calcium binding protein calsequestrin respectively. We recognize two stages at which important events in membrane morphogenesis occur. The first stage coincides with early myofibrillogenesis (starting at approximately embryonal day E5.5), and it involves the assembly of calcium release units at the periphery of the muscle fibre in which feet and the internal protein are identified. Groups of tetrads also are present at very early stages and their disposition indicates a relation to the feet of peripheral couplings. Thus three major components of the excitation-contraction coupling pathway are in place as soon as myofibrils develop. The density of groups of tetrads in the surface membrane of primary and secondary fibres is similar, despite differences in developmental stages. The second stage involves the formation of a complex transverse tubule network and of internal sarcoplasmic reticulum-transverse tubule junctions, while peripheral couplings disappear. This stage starts abruptly (between E15 and E16) and simultaneously in primary and secondary fibres. It coincides with the myotube-to-myofibre transition. The two stages are separated by a relatively long intervening period (between E9 and E16). During the latter part of this period some primitive transverse tubules appear, and form junctions with the sarcoplasmic reticulum, but they remain strictly located at the periphery of the fibre and are not numerous. Finally, after the second stage there is a prolonged (up to 4 weeks) period of maturation, during which density of free sarcoplasmic reticulum increases, triads acquire a location at the A-I junction and fibre type differences appear. We conclude that a system for calcium uptake, storage and release exists at the periphery of the myotube during early myogenesis. The complexity of the system and its ability to deliver calcium through the entire fibre develop in parallel to the formation of myofibrils.

Postnatal development of rabbit fast-twitch skeletal muscle: accumulation, isoform transition and fibre distribution of calsequestrin

The time-course of disappearance of slow-cardiac calsequestrin (CS) and that of appearance of the skeletal CS isoform were investigated in developing fast-twitch skeletal muscle of the rabbit between postnatal days 1 and 60, along with changes in density of the ryanodine receptor (RyR)/Ca2+ release channel. Western blot data on skeletal muscle membranes, purification of two CS isoforms by phenyl-Sepharose chromatography, and their immunolocalization in muscle fibres, all show that both CS isoforms are coexpressed in neonatal muscles. Our results, at the protein level, indicate that the turning off of synthesis of cardiac CS and its total disappearance from fast-twitch fibres take place at critical periods between two and four weeks postnatally, i.e. past changes in the respective mRNA. In contrast, the accumulation in muscle membranes of both the RyR and the skeletal CS isoform proceeds steadily up to one month, to reach adult values at about two months of age. These findings seem to argue that myogenic factors, in addition to the morphogenetic influence on the sarcoplasmic reticulum from the neural input to the muscle, may be involved in the developmental transition of CS isoforms in mammalian fast-twitch muscle fibres.