Generation of a monoclonal antibody reactive to prefusion myocytes

We established a novel monoclonal antibody, Yaksa that is specific to a subpopulation of myogenic cells. The Yaksa antigen is not expressed on the surface of growing myoblasts but only on a subpopulation of myogenin-positive myocytes. When Yaksa antigen-positive mononucleated cells were freshly prepared from a murine myogenic cell by a cell sorter, they fused with each other and formed multinucleated myotubes shortly after replating while Yaksa antigen-negative cells scarcely generated myotubes. These results suggest that Yaksa could segregate fusion-competent, mononucleated cells from fusion–incompetent cells during muscle differentiation. The Yaksa antigen was also expressed in developing muscle and regenerating muscle in vivo and it was localized at sites of cell–cell contact between mono-nucleated muscle cells and between mono-nucleated muscle cells and myotubes. Thus, Yaksa that marks prefusion myocytes before myotube formation can be a useful tool to elucidate the cellular and molecular mechanisms of myogenic cell fusion.     

The organogenesis of murine striated muscle: A cytoarchitectural study

The ultrastructure and the three-dimensional cytoarchitecture of the developing murine extensor digitorum longus muscle has been studied in spaced, serial, transverse and longitudinal ultrathin sections of the muscles of 12-, 14-, 16-, and 18-day in utero, newborn, and 5-day-old 129 ReJ mice. Despite the fact that in vivo myogenesis is asynchronous (i.e., during most of the fetal period, multiple stages of myogenesis can be seen in a single developing muscle mass), a distinct temporal pattern of development can be seen across the entire width and length of the developing muscle. At 12 days in utero, the developing extensor digitorum longus muscle consists of primary myotubes surrounded by a pleomorphic population of mononucleated cells devoid of myofilaments. At this stage, blood vessels and nerves are found peripheral to but not within the developing muscle mass. A delay of ≥ 2 days occurs between the time of formation of the primary and secondary myotubes. Clusters (consisting of one primary myotube and secondary myotubes), axon bundles, capillaries, and primitive motor endplates are found in the muscle by 16 days in utero. Evidence is presented consistent with the hypothesis that cluster formation and cluster dispersal occur simultaneously in the developing muscle, beginning as early as 16-days in utero. By 18 days in utero, many of the primary myotubes of the cluster and the independent myotubes (i.e., single myotubes enclosed in their own basal lamina) have begun to acquire the polygonal shape, fascicular arrangement, and ultrastructure characteristic of more mature myofibers. At birth, clusters are infrequently encountered, and intramuscular axons have begun to undergo myelination. At this time, the only undifferentiated, mononucleated cells present in the muscle are myosatellite cells. The first week postnatal was characterized by further maturation of the myofibers.     

An ultrastructural study of the dufferentiation of skeletal muscle in the bovine fetus

Summary The differentiation of skeletal muscle was studied by electron microscopy in bovine fetuses from 47 days gestation to neonatal calves 3 days of age.Initally, the muscle was composed of clusters of myotubes with mononucleated myoblasts between them. In 2-month-old fetuses these myoblasts became apposed to the differentiating muscle cells and were enclosed within the rudimentary basal lamina of the myotubes. At this stage the clusters of myotubes consisted of central, larger diameter, more differentiated myotubes and also the mononucleated satellite cells. The differentiated myotubes separated from the clusters accompanied by satellite cells which continued proliferating and fused together to form new generations of satellite myotubes. In this manner new clusters of myotubes were formed. By 4–5 months some of the separating myotubes began to form individual myotubes and independent myofibers were prominent in fetuses of 5–8 months of age.The myofibers in the 8-month-old fetuses showed diversification into fiber types by differences in the thickness of the Z-line, the prominence of the sarcotubular system, the amount of glycogen and lipid droplets and also the number of mitochondria.     

Expression and organization of muscle specific proteins during the early developmental stages of the rabbit heart

Summary The expression and intracellular distribution patterns of muscle-specific proteins were studied during rabbit embryo development (7–13 dpc) using monoclonal antibodies against titin, myosin, tropomyosin and actin, as well as the intermediate filament proteins desmin, keratin and vimentin. From our panel, titin appeared to be the first muscle-specific protein to be exclusively expressed in the embryonic rabbit heart. Upon differentiation (myocyte and myotube formation), titin reorganizes from dot-like aggregates into a cross-striated pattern (in 9- to 30-somite embryos) via a transiently filamentous distribution. When the expression and organization of the other muscle proteins was studied in relation to titin, it became apparent that tropomyosin followed upon titin with respect to its exclusive expression in the heart anlagen and its organization into a striated pattern. Myosin and desmin were organized into cross-striated patterns after titin and tropomyosin, but this arrangement had not reached its final form in 13-dpc embryos. Actin, keratin and vimentin were distributed in cytoplasmic filaments in the embryonic stages we investigated. Since the first pulsations are already detected in 3-somite embryos, we conclude that the organization of titin, tropomyosin, myosin and desmin into a striated pattern does not seem to be essential for the initiation of muscle cell contraction in the heart anlagen. Furthermore, this study shows that, in comparison with studies on mouse, chick and rat, the sequence of expression of muscle-specific and intermediate filament proteins during cardiomyogenesis is species-dependent, and that their expression and organization varies in time in different regions of the developing heart.Abbreviations IFP intermediate filament proteins - PBS phosphate-buffered saline - FITC fluorescein isothiocyanate - TRITC tetramethylrhodamine isothiocyanate - TxRd texas red - dpc days post conception     

Passive stiffness changes in soleus muscles from desmin knockout mice are not due to titin modifications

Passive stiffness was found to be increased in mouse soleus muscles lacking desmin. Because titin is considered to be the major source of muscle elasticity, the stiffening might be explainable by titin adaptation. To test this, passive mechanical properties of single skinned fibres of soleus muscles from desmin knockout and control mice were analysed by using various extension tests. Titin expression was studied by SDS-gel electrophoresis. Absence of desmin did not modify either electrophoretic mobility of the titin band (3700 kDa) or optical density-unit ratios between bands for titin and nebulin (congruent with 0.3) and bands for titin and myosin heavy chain (congruent with 0.08). Elastic properties of fibres were not altered in the absence of desmin since passive tensions were similar under quasi-static (56-66 kN m(-2)) and dynamic (100-118 kN m(-2)) conditions whatever the kind of fibre. Thus, titin is unlikely to be responsible for the large increase in passive stiffness observed in whole soleus muscles when desmin is lacking.     

Desmin-lacZ transgene expression and regeneration within skeletal muscle transplants

The purpose of this study was to investigate the initiation and time course of the regeneration process in fragments of skeletal muscle transplants as a function of muscle tissue age at implantation. The appearance of desmin occurs at the very beginning of myogenesis. The transgenic desminnls lacZ mice used in the study bear a transgene in which the 1 kb DNA 5′ regulatory sequence of the desmin gene is linked to a reporter gene coding for Escherichia coliβ-galactosidase. The desmin lacZ transgene labels muscle cells in which the desmin synthesis programme has commenced. We implanted pectoralis muscle fragments from fetal transgenic embryos and mature and old transgenic mice into mature non-transgenic mice. Early events of myogenesis occurring during regeneration started sooner in transplants from 4-month-old (day 3 post-implantation) muscle than in those from 24-month-old (day 5-6 post-implantation) muscle, and they lasted longer in those from young (day 17 post-implantation) than in those from old (day 14 post-implantation) muscle fragments. In adult muscle, transgene activation proceeded from the periphery toward the centre of the transplant. In transplants from fetal 18-day-old pectoralis, myotubes with transgene activity were observed from day 1 to day 19. Desmin immunoreactivity, which appeared about one day after transgene activation, was followed by myosin expression. In adult transplants, the continuity of laminin labelling was disrupted around degenerative fibres, illustrating alteration of the extracellular matrix. Our data suggest that satellite cells from old muscle tissue have lower proliferative capacity and/or less access to trophic substances released by the host (damaged fibres, vascularization) than those from fetal or young adult muscle This revised version was published online in July 2006 with corrections to the Cover Date.     

The expression pattern of contractile and intermediate filament proteins in developing skeletal muscle and rhabdomyosarcoma of childhood: Diagnostic and prognostic utility

In order to investigate whether rhabdomyosarcoma (RMS) can be related to equivalent stages of skeletal muscle development, muscle tissue of 21 human foetuses and 112 primary RMSs were characterized immunohistochemically using antibodies directed against vimentin, desmin, muscle-specific actin (HHF35), sarcomeric actin (sr-actin), smooth muscle actin (sm-actin), and troponin-T. During fetal skeletal muscle development, all myotubes/fibres of the first and second generations expressed desmin, HHF35, and sr-actin. Vimentin was almost exclusively present in immature primary and secondary myotubes/fibres. Troponin-T was expressed in immature myotubes/fibres of the first and second generations as well as mature fibres of the second generation. Sm-actin was never expressed. Vimentin was expressed in 96 per cent of primary and 98 per cent of relapsed RMS; HHF35 in 96 and 98 per cent, respectively; desmin in 95 and 100 per cent; troponin-T in 82 and 75 per cent; sr-actin in 71 and 86 per cent; and sm-actin in 13 and 17 per cent. The proportion of RMS cells reacting with vimentin, HHF35, and desmin was consistently higher than those expressing sr-actin and troponin-T. Neither the shape nor size of neoplastic RMS cells nor the histopathological types were related to the expression pattern of the investigated markers. RMS with aberrant expression of two or more markers predicted a worse prognosis than RMS in which at most one marker was aberrantly expressed (25 per cent and 54 per cent 10-year survival, P=0·01). These results demonstrate that HHF35, desmin, sr-actin, and troponin-T have the potential to confirm the commitment of the tumours to the myogenic pathway which supports the diagnosis of RMS. However, it was impossible to relate RMS to equivalent stages of skeletal muscle development. Aberrant marker expression by RMS cells correlated significantly with patients' survival.     

Mammalian myoblasts become fast or slow myocytes within the somitic myotome

Summary A monoclonal antibody has been prepared to slow skeletal muscle type myosin heavy chain which in the rat distinguishes fast and slow myocytes within the somitic myotome at 11.5 days in utero. The distribution of slow myotubes identified by this antibody in developing limb buds is also restricted to presumptive slow muscle cell type regions only. No slow myoblasts in hindlimb buds, however, were detected at 14.5 day in utero when a small number of fast muscle cells were already present. The presence of slow muscle cell population detected by this specific antibody became apparent a day later. This study thus demonstrated the diversification into different muscle cell types during both early embryonic and foetal development.     

Ablation of the fetal mouse spinal cord: the effect on soleus muscle cytoarchitecture.

A technique is described whereby it is possible to surgically ablate the lumbosacral spinal cord of a developing mouse fetus without interfering with fetal viability. The lumbosacral spinal cords of 14-day in utero, 129ReJ mice were ablated with a Cooper Nd-YAG laser, and the fetuses, enclosed in their membranes and attached to the uterus by their placentae, were allowed to develop in the abdominal cavity of the dam. The cytoarchitecture and the temporal pattern of organogenesis of aneural soleus muscles were studied in spaced, serial, transverse, ultrathin sections of muscles of 16- and 18-day gestation and newborn (20-day gestation) mice. At the time of surgery, the soleus muscle was a discrete mass consisting of primary myotubes and a pleomorphic population of mononucleated cells. Axon bundles and blood vessels were found at the muscle's periphery, but had not penetrated throughout the muscle mass. The organogenesis of the aneural muscle was remarkably similar to that of the innervated soleus muscle (Ontell et al., Am J Anat 181:267-278, 1988). In the aneural muscle, as in the innervated muscle, significant numbers of secondary myotubes formed all along the lengths of primary myotubes. Moreover, the time course of myotube formation, the dynamics of cluster formation and cluster dispersal, and the ultrastructural appearance of the myotubes mimicked that observed in innervated muscle. The frequency of necrotic myotubes was no greater in the aneural muscle than in the innervated soleus muscle. Myotube maturation was similar in aneural and innervated soleus muscles until 18 days gestation. However, at birth, aneural myotubes appeared to be slightly less mature than innervated myotubes. Thus, the major morphogenic phenomena that characterize the development of the soleus muscle appear to be independent of innervation.     

Distribution and organization of desmin in cultured adult cardiac muscle cells: reflection on function

The cell-culture model for the study of desmin in adult cardiac muscle cells has provided insight into the function of desmin based on its distribution and structural organization. Initially, desmin emerged as a filamentous network from the existing amorphous form in the growing adult cardiac myocytes in vitro. Later, desmin became organized in various forms. In addition to the presence of a periodic array of desmin in the Z-line regions as observed in cardiac myocytes in vivo, longitudinally and transversely oriented strands of desmin were observed along the length of myofibrils in cardiac myocytes in vitro. These desmin strands and transverse perodicities formed a complex interwoven network, interlacing myofibrils of cells. Desmin and agr;-actinin were organized in ribbon- or aponeuroses-like structures that appeared as sheet-like, supportive structures for the cell body. The cellular cytoplasmic processes containing myofibrils were supported by desmin bars. The complex desmin network, desmin bars, transverse strands and ribbons or aponeuroses were observed in in vitro cardiac myocytes in contrast to in vivo cardiac myocytes. The functional implication of desmin, as indicated by in vivo studies, required more information concerning the organization of desmin for its supportive function, and is addressed in the present study. The elaborate organization of desmin provides evidence for its supportive function for the maintenance of the structural integrity and function of cardiac muscle cells.     

Cytoarchitecture of the fetal murine soleus muscle

The organogenesis of the soleus muscle of the 120 ReJ mouse (a mixed muscle, which in the adult contains approximately equal numbers of slow-twitch oxidative and fast-twitch oxidative-glycolytic myofibers) was studied in spaced, serial transverse, and longitudinal sections of muscles of 14-, 16-, and 18-day in utero and 1- and 5-day postnatal mice. A discrete soleus muscle was distinguished by 14 days in utero. It consisted of groups of closely apposed primary myotubes displaying junctional complexes and a pleo-morphic population of mononucleated cells. Between 14 and 16 days in utero there was little de novo myotube formation. At 16 days in utero, basal lamina surrounded groups of primary myotubes; and primitive motor endplates were found on these myotubes. At 18 days in utero, the basal-lamina-enclosed groups of primary myotubes were no longer present. At this stage, basal lamina surrounded clusters (consisting of one primary myotube and one or more secondary myotubes) or independent myotubes (single myotubes surrounded by their own basal lamina). Cluster formation and cluster dispersal occurred concurrently, beginning at 18 days in utero and extending until birth. At birth, there was still a substantial population of immature, secondary myotubes that interdigitated with larger, more mature primary myofibers. At this stage, intermuscular axons had begun to myelinate, and posteynaptic specialization of the motor endplates had begun. Cluster dispersal and myonuclear migration was completed during the first 5 days postnatally with the muscle taking on adult characteristics. Beginning at 16 days in utero and extending into the neonatal period, there was evidence of myotube death in the soleus muscle.     

Regeneration of single skeletal muscle fibers in vitro.

A culture system utilizing single skeletal muscle fibers from adult rats was developed to study the origin and behavior of mononucleated myoblasts during muscle regeneration. The single fibers are removed manually from the leg and thigh muscles at 300-400 gm rats and maintained in vitro embedded in a fibrin clot overlain with culture medium. Regenerative events were monitored by continuous observations of the cultured fibers. During the first few hours in vitro the fibers undergo degenerative changes including the formation of myofibrillar contraction clots and pyknosis of myonuclei. The endomysial tube (basement lamina) remains intact along the entire length of the fiber and forms transparent chambers bridging the contraction clots. Single fibers are free of endomysial cells and display no cellular outgrowth in cultures, except at the cut ends. In contrast, a rich outgrowth of endomysial connective tissue cells is found with bundles consisting of two or more fibers. Isolated mononucleated cells, presumed to be muscle satellite cells, are present within the endomysial tube of single fibers at the onset of the culture period. There is no evidence that myonuclei contribute to the formation of mononucleated cells. The satellite cells enlarge and begin to proliferate during the second day in vitro to form clones of presumptive myoblasts within the endomysial tube. The early clones have a cell doubling time of about 22 hours and exhibit mitotic synchrony. After 5-7 days in vitro the satellite cell progeny begin to fuse to form multinucleated myotubes within the endomysial tube of the original fiber. The myotubes display spontaneous contractile activity and may extend throughout the length of the endomysial tube.     

C2C12细胞诱导构建三维骨骼肌组织

目的 利用修饰并铸型后的Sylgard 184凹槽与C2C12细胞复合培养、诱导分化,获取三维极性骨骼肌组织. 方法 Sylgard 184双组分以10∶1的比例均匀混合并倒板,室温下静置固化并对其表面压槽铸型,Hank液冲洗凹槽,Matrigel和胶原的混合液均匀铺被凹槽底部,置生物安全柜待细胞基质自然干燥、紫外线照射消毒1h以上时接种C2C12细胞悬液,细胞增殖约80%汇合时改用分化培养基进行分化诱导,倒置显微镜下观察肌管的分化状态, RT-PCR方法检测肌管内myogenin和desmin基因mRNAs的表达,免疫荧光检测生肌转录因子myogenin和desmin蛋白的表达,扫描电镜观察肌管形态和肌管间的连接. 结果 C2C12细胞在Sylgard 184弹性体铸型压槽中培养分化7d后,倒置显微镜下可见肌管呈极性分化,且肌管之间融合紧密;21d后,扫描电镜检测可见肌管之间排列紧密且相互重叠,形成膜样结构,厚度可达0.15mm,具有三维性;RT-PCR、免疫荧光检测证实极性分化肌管内具有myogenin和desmin的阳性表达. 结论 修饰并铸型的Sylgard 184凹槽具有一定的方向引导效应,能促进C2C12细胞分化形成多核肌管,且肌管呈极性重叠排列,形成三维极性骨骼肌组织结构.     

Intermediate filament proteins in TPA-treated skeletal muscle cells in culture

Summary The cocarcinogenic phorbol ester 13-tetradecanoyl-O-phorbol acetate selectively and reversibly inhibits the ongoing differentiation programme of chick muscle cells in culture. 13-tetradecanoyl-O-phorbol acetate promptly blocks spontaneous contractions in mature myotubes and induces them to retract, forming giant myosacs and concurrently stress fibre-like structures are assembled. Using indirect immunofluorescence to localise desmin, the muscle specific intermediate filament protein, it was shown that its distribution is longitudinally oriented in mature myotubes. In myosacs, desmin has a reticular pattern although not as linearly oriented as in control myotubes. Using gel electrophoresis of control and 13-tetradecanoyl-O-phorbol acetate treated cell extracts, three major protein bands were observed with molecular weight of 43, 50 and 55 kDa. They migrate as actin, desmin and vimentin, respectively. The 50 kDa and 55 kDa proteins were expressed more in 13-tetradecanoyl-O-phorbol acetate-treated cells. The 50 kDa band was confirmed as desmin by immunoblotting using anti-chicken desmin antibody. Two-dimensional gel electrophoresis analysis showed the appearance of more acidic isoforms of the 50 and 55 kDa proteins 13-tetradecanoyl-O-phorbol in acetate-treated cells. The 43 kDa protein was seen as three distinct isoforms in control cells and as only two isoforms in 13-tetradecanoyl-O-phorbol acetate-treated cells.     

Regeneration of single skeletal muscle fibers in vitro

A culture system utilizing single skeletal muscle fibers from adult rats was developed to study the origin and behavior of mononucleated myoblasts during muscle regeneration. The single fibers are removed manually from the leg and thigh muscles of 300–400 gm rats and maintained in vitro embedded in a fibrin clot overlain with culture medium. Regenerative events were monitored by continuous observation of the cultured fibers. During the first few hours in vitro the fibers undergo degenerative changes including the formation of myofibrillar contraction clots and pyknosis of myonuclei. The endomysial tube (basement lamina) remains intact along the entire length of the fiber and forms transparent chambers bridging the contraction clots. Single fibers are free of endomysial cells and display no cellular outgrowth in culture, except at the cut ends. In contrast, a rich outgrowth of endomysial connective tissue cells is found with bundles consisting of two or more fibers. Isolated mononucleated cells, presumed to be muscle satellite cells, are present within the endomysial tube of single fibers at the onset of the culture period. There is no evidence that myonuclei contribute to the formation of mononucleated cells. The satellite cells enlarge and begin to proliferate during the second day in vitro to form clones of presumptive myoblasts within the endomysial tube. The early clones have a cell doubling time of about 22 hours and exhibit mitotic synchrony. After 5–7 days in vitro the satellite cell progeny begin to fuse to from multinucleated myotubes within the endomysial tube of the original fiber. The myotubes display spontaneous contractile activity and may extend throughout the length of the endomysial tube.     

Fusion-independent expression of functional ACh receptors in mouse mesoangioblast stem cells contacting muscle cells

Mesoangioblasts are vessel-associated fetal stem cells that can be induced to differentiate into skeletal muscle, both in vitro and in vivo . Whether this is due to fusion or to transdifferentiation into bona fide satellite cells is still an open question, for mesoangioblasts as well as for other types of stem cells. The early steps of satellite cell myogenic differentiation involve MyoD activation, membrane hyperpolarization and the appearance of ACh sensitivity and gap junctional communication. If mesoangioblasts differentiate into satellite cells, these characteristics should be observed in stem cells prior to fusion into multinucleated myotubes. We have investigated the functional properties acquired by mononucleated green fluorescent protein (GFP)-positive mesoangioblasts co-cultured with differentiating C2C12 myogenic cells, using the patch-clamp technique. Mesoangioblasts whose membrane contacted myogenic cells developed a hyperpolarized membrane resting potential and ACh-evoked current responses. Dye and electrical coupling was observed among mesoangioblasts but not between mesoangioblasts and myotubes. Mouse MyoD was detected by RT-PCR both in single, mononucleated mesoangioblasts co-cultured with C2C12 myotubes and in the total mRNA from mouse mesoangioblasts co-cultured with human myotubes, but not in human myotubes or stem cells cultured in isolation. In conclusion, when co-cultured with muscle cells, mesoangioblasts acquire many of the functional characteristics of differentiating satellite cells in the absence of cell fusion, strongly indicating that these stem cells undergo transdifferentiation into satellite cells, when exposed to a myogenic environment.     

Association of plectin with Z-discs is a prerequisite for the formation of the intermyofibrillar desmin cytoskeleton

Plectin is a high-molecular mass protein (approximately 500 kd) that binds actin, intermediate filaments, and microtubules. Mutations of the plectin gene cause a generalized blistering skin disorder and muscular dystrophy. In adult muscle, plectin is colocalized with desmin at structures forming the intermyofibrillar scaffold and beneath the plasma membrane. To study the involvement of plectin in myofibrillogenesis, we analyzed the spatial and temporal expression patterns of plectin in cultured differentiating human skeletal muscle cells and its relationship to desmin intermediate filaments during this process. Northern and Western blot analyses demonstrated that at least two different plectin isoforms are expressed at all developmental stages from proliferating myoblasts to mature myotubes. Using immunocytochemistry, we show that the localization of plectin dramatically changes from a network-like distribution into a cross-striated distribution during maturation of myocytes. Double immunofluorescence experiments revealed that desmin and plectin are colocalized in premyofibrillar stages and in mature myotubes. Interestingly, plectin was often found to localize to the periphery of Z-discs during the actual alignment of neighboring myofibrils, and an obvious cross-striated plectin staining pattern was observed before desmin was localized in the Z-disc region. We conclude that the association of plectin with Z-discs is an early event in the lateral alignment of myofibrils that precedes the formation of the intermyofibrillar desmin cytoskeleton.     

Inhibition of fasL sustains phagocytic cells and delays myogenesis in regenerating muscle fibers

Macrophage-muscle cell interactions are complex, and the majority is unknown. The persistence of inflammatory cells in skeletal muscle could be critical for myofiber viability. In the present paper, we show that FasL plays a role in the resolution of muscle inflammation. We analyzed inflamed muscles of normal mice treated from day 3 to day 8 with a FasL inhibitor (Fas-Ig) or with control Ig. Treated muscles were collected at 3, 5, and 10 days. The treatment with recombinant Fas-Ig protein induced a severe persistence of inflammatory cells at 5 days (115,000+/-27,838 vs. 41,661+/-6848, p<0.01) and 10 days from injury (145,500+/-40,850 vs. 5000+/-1000, p<0.001). Myofiber regeneration was highly impaired (37+/-14 vs. 252+/-28, p<0.01). Apoptosis of phagocytic cells was absent during Fas-Ig treatment (0.9+/-0.6 vs. 1300+/-150, p<0.0001), but apoptotic, mononucleated cells appeared at day 10, 2 days after the suspension of Fas-Ig administration. The time course of FasL expression during muscle inflammation, at mRNA and protein level, reveals a peak during myoblast proliferation. The peak of FasL expression coincides with the peak of apoptosis of phagocytic cells. In situ hybridization shows the co-expression of FasL and MyoD mRNA in mononucleated cells, i.e., myoblasts. Experiments on the myoblast cell culture confirmed the expression of FasL in myoblasts. The findings shown here indicate one of the pathways to control myoblast-macrophage interaction and might be relevant for the control of inflammatory cells in muscle tissue. Perhaps altering FasL expression with recombinant proteins could ameliorate inflammation in degenerative myopathies and up-regulate muscle regeneration.