Effects of 20(S)-hydroxycholesterol on satellite cell proliferation and differentiation of broilers.

In the modern poultry industry, with increasing product demand, muscle growth rate and meat yield in chickens have tremendously changed. Understanding the regulation of muscle development is important to maintain efficient growth and development in meat-type chickens. 20(S)-hydroxycholesterol (20S) is known as one of the naturally occurring osteogenic cholesterol derivatives due to its ability to induce osteogenic differentiation; however, no studies have evaluated myogenic response to 20S in chicken muscle cells. To determine the use of 20S in vitro for the proliferation and differentiation of chicken satellite cells, satellite cells were isolated from pectoralis major muscle of 4-week-old Ross 708 male chickens and subjected to 0.25, 0.5, and 1.0 µmol of 20S during their proliferation and differentiation stages. Cell proliferation and differentiation were measured every 24 h for 72 h by determining DNA concentration, the activity of creatine kinase, and the expressions of myogenic regulatory transcription factors. Together these results suggested that a lower concentration of 20S did not affect myogenesis but a high concentration of 1.0 µmol 20S can negatively affect proliferation and differentiation in chicken satellite cells.

Effect of growth selection of broilers on breast muscle satellite cell function: Response of satellite cells to NOV, COMP, MYBP-C1, and CSRP3.

The wooden breast (WB) myopathy is characterized by the palpation of a hard pectoralis major muscle that results in the necrosis and fibrosis of muscle fibers in fast-growing heavy weight meat-type broiler chickens. Necrosis of existing muscle fibers requires the repair and replacement of these myofibers. Satellite cells are responsible for the repair and regeneration of myofibers. To address how WB affects satellite cell function, top differentially expressed genes in unaffected and WB-affected pectoralis major muscle determined by RNA-Sequencing were studied by knocking down their expression by small interfering RNA in proliferating and differentiating commercial Ross 708 and Randombred (RBch) satellite cells. RBch satellite cells are from commercial 1995 broilers before WB appeared in broilers. Genes studied were: Nephroblastoma Overexpressed (NOV); Myosin Binding Protein-C (MYBP-C1); Cysteine-Rich Protein 3 (CSRP3); and Cartilage Oligomeric Matrix Protein (COMP). Ross 708 satellite cells had greatly reduced proliferation and differentiation compared to RBch satellite cells. MYBP-C1, CSRP3, and COMP reduced late proliferation and NOV did not affect proliferation in both lines. The timing of the knockdown differentially affected differentiation. If the expression was reduced at the beginning of proliferation, the effect on differentiation was greater than if the knockdown was at the beginning of differentiation. These data suggest, appropriate gene expression levels during proliferation greatly impact multinucleated myotube formation during differentiation. The effect of slow myofiber genes MYBP-C1 and CSRP3 on proliferation and differentiation suggests the presence of aerobic Type I satellite cells in the pectoralis major muscle which contains anaerobic Type IIb cells.

Response of turkey pectoralis major muscle satellite cells to hot and cold thermal stress: Effect of growth selection on satellite cell proliferation and differentiation.

Satellite cell (SCs), the main progenitors for post-hatch poultry muscle growth, has maximal mitotic activity and sensitivity to temperature during the first week after hatch. The objective of the present study was to determine the effect of hot and cold temperatures on the proliferation and differentiation of SCs from pectoralis major (P. major) muscle of fast-growing 1-week-old Nicholas commercial (NC) turkeys compared to Randombred Control Line 2 (RBC2) turkeys representing commercial turkeys from 1966. Three temperature regimens were used: SCs proliferation at 38 °C (control) with differentiation at 43° or 33 °C; proliferation at 43° or 33 °C with differentiation at 38 °C; or both proliferation and differentiation at 43°, 38°, or 33°C. Satellite cell proliferation and differentiation increased at 43 °C and decreased at 33 °C in both lines. When a thermal challenge was administered during proliferation, greater stimulatory or suppressive effects on differentiation were observed compared to if the thermal challenge was applied only during differentiation in both lines. Expression of myoblast determination protein 1 during proliferation showed a higher increase in the NC line compared to the RBC2 line at 43 °C. Increased myogenin expression was observed in all hot treatment groups in the NC line but was only observed in the RBC2 line if the hot treatment was administered throughout proliferation and differentiation. Cold treatment suppressed myogenin expression independent of line. These results suggest turkey P. major muscle SCs are more sensitive to environmental temperatures during proliferation, and SCs from growth-selected NC turkeys are more sensitive to thermal stress compared to the RBC2 turkeys.

Effect of early posthatch supplementation of vitamin E and omega-3 fatty acids on the severity of wooden breast, breast muscle morphological structure, and gene expression in the broiler breast muscle.

Wooden breast (WB) has arisen primarily in the breast muscle of commercial broilers. It is characterized by palpation of a rigid pectoralis major (p. major) muscle and is under severe oxidative stress and inflammation. Previous studies have shown that vitamin E (VE) has antioxidant properties and omega-3 (n-3) fatty acids have an anti-inflammatory effect. The objectives of this study were to identify the effects of VE and n-3 fatty acids on the severity of WB, morphological structure of the p. major muscle, expression of genes likely associated with WB and to determine the most beneficial supplementation period. A total of 210 Ross 708 broilers were randomly assigned into 7 treatments with 10 replicates of 3 birds each. The control group received a corn-soybean meal basal diet during the entire study (0-58 d). Supplementation of VE (200 IU/kg), n-3 fatty acids (n-6/n-3 ratio of 3.2:1), or combination of both were fed during the starter phase (0-10 d) or grower phase (11-24 d). All broilers were harvested at 58 d of age. Morphological assessment of the p. major muscle included myofiber width, perimysial and endomysial connective tissue space, overall morphological structure, and scoring of WB microscopically. Gene expression was measured using nanostring analysis. Genes associated with muscle development and growth factors, inflammation, extracellular matrix, and glucose metabolism were differentially expressed in the p. major muscle of the broilers supplemented with VE in the grower diet. Greater than 2 times more giant myofibers (≥70 µm) were found in the group supplemented with VE and n-3 fatty acids in the starter diet compared with the group fed VE in the grower diet (P = 0.02). Microscopic evaluation showed that VE supplementation in the grower diet had a 16.19% increase in muscle with no WB compared with the control group (P = 0.05). These data suggest that supplementation of VE during the grower phase may reduce the severity of WB in broilers.

Krüppel-like factor KLF9 inhibits chicken intramuscular preadipocyte differentiation.

1. Poultry meat quality is affected by many factors, among which intramuscular fat (IMF) is predominant. IMF content affects tenderness, juiciness and flavour of meat. Krüppel-like transcriptional factors (KLFs) are important regulators of adipocyte differentiation. However, little is known about the KLF9 gene associated with poultry IMF deposition, especially intramuscular adipocyte differentiation.2. Previous work has shown that chicken KLF9 was differentially expressed during adipogenesis of intramuscular preadipocytes differentiation. In this study, the function of KLF9 in chicken intramuscular preadipocytes differentiation was investigated.3. In the chicken preadipocyte differentiation model, KLF9 expression showed a major increase with adipogenic induction. Overexpression of KLF9 down-regulated the expression of the adipogenic marker gene AP2, and impaired triglyceride accumulation. Knockdown of KLF9 in chicken intramuscular preadipocytes increased the expression of PPARG, CEBPA and AP2. In addition, it was proposed that KLF9 may regulate adipogenesis via lncRNAs NONGGAT002209.2, NONGGAT003346.2, NONGGAT000436.2 and NONGGAT006302.2 in chicken.4. The data supported a novel role of KLF9 in regulating chicken intramuscular preadipocyte differentiation. Such findings may contribute to a more thorough understanding of chicken IMF deposition and the improvement of poultry meat quality.

Superficial and deep changes of histology, texture and particle size distribution in broiler wooden breast muscle during refrigerated storage.

Recently the poultry industry faced an emerging muscle abnormality termed wooden breast (WB), the prevalence of which has dramatically increased in the past few years. Considering the incomplete knowledge concerning this condition and the lack of information on possible variations due to the intra-fillet sampling locations (superficial vs. deep position) and aging of the samples, this study aimed at investigating the effect of 7-d storage of broiler breast muscles on histology, texture, and particle size distribution, evaluating whether the sampling position exerts a relevant role in determining the main features of WB. With regard to the histological observations, severe myodegeneration accompanied by accumulation of connective tissue was observed within the WB cases, irrespective of the intra-fillet sampling position. No changes in the histological traits took place during the aging in either the normal or the WB samples. As to textural traits, although a progressive tenderization process took place during storage (P ≤ 0.001), the differences among the groups were mainly detected when raw meat rather than cooked was analyzed, with the WB samples exhibiting the highest (P ≤ 0.001) 80% compression values. In spite of the increased amount of connective tissue components in the WB cases, their thermally labile cross-links will account for the similar compression and shear-force values as normal breast cases when measured on cooked samples. Similarly, the enlargement of extracellular matrix and fibrosis might contribute in explaining the different fragmentation patterns observed between the superficial and the deep layer in the WB samples, with the superficial part exhibiting a higher amount of larger particles and an increase in particles with larger size during storage, compared to normal breasts.

Satellite cells isolated from skeletal muscle will proliferate faster in WENS yellow feather chicks.

This study was conducted to evaluate the differential proliferation ability of satellite cells (SCs) derived from pectoral muscles (PM) with different fiber characteristics and further to explore the underlying molecular mechanism. WENS Yellow Feather Chicks (WYFC) were chosen as the animal model, with White Plymouth Rock Chicks (WPRC) as a comparison. The results showed that WPRC had higher body and pectoral muscle weight than WYFC at 4 days old (P < 0.05). However, WYFC showed greater fiber numbers/mm(2) but smaller fiber cross-sectional area compared with WPRC in PM (P < 0.05). SCs derived from PM of WYFC had a faster proliferation rate but smaller cell size compared with that from PM of WPRC (P < 0.05). The percentage of cell population in G2/M phase and the messenger RNA abundance of TSC1 (P = 0.08), Rheb (P = 0.07) and target of rapamycin (TOR, P = 0.06) in WYFC were higher than that in WPRC. In conclusion, our results demonstrated that SCs isolated from PM of WYFC had faster proliferation rate but smaller cell size than that in WPRC. The higher SC proliferation in WYFC may be due to higher gene expression of TOR signaling pathway than in WPRC, and the larger cell size of WPRC may be due to higher insulin-like growth factor-1 expression than in WYFC.

Transcriptome analysis of post-hatch breast muscle in legacy and modern broiler chickens reveals enrichment of several regulators of myogenic growth.

Agriculture provides excellent model systems for understanding how selective pressure, as applied by humans, can affect the genomes of plants and animals. One such system is modern poultry breeding in which intensive genetic selection has been applied for meat production in the domesticated chicken. As a result, modern meat-type chickens (broilers) exhibit enhanced growth, especially of the skeletal muscle, relative to their legacy counterparts. Comparative studies of modern and legacy broiler chickens provide an opportunity to identify genes and pathways affected by this human-directed evolution. This study used RNA-seq to compare the transcriptomes of a modern and a legacy broiler line to identify differentially enriched genes in the breast muscle at days 6 and 21 post-hatch. Among the 15,945 genes analyzed, 10,841 were expressed at greater than 0.1 RPKM. At day 6 post-hatch 189 genes, including several regulators of myogenic growth and development, were differentially enriched between the two lines. The transcriptional profiles between lines at day 21 post-hatch identify 193 genes differentially enriched and still include genes associated with myogenic growth. This study identified differentially enriched genes that regulate myogenic growth and differentiation between the modern and legacy broiler lines. Specifically, differences in the ratios of several positive (IGF1, IGF1R, WFIKKN2) and negative (MSTN, ACE) myogenic growth regulators may help explain the differences underlying the enhanced growth characteristics of the modern broilers.

Histological findings of an autologous dermal fat graft implanted onto the pectoralis major muscle of a rat model.

BACKGROUND: The aim of this study was to investigate the maintenance of volume as a spacer by comparing vascular supply and apoptosis in an implanted autologous-free dermal fat graft (FDFG) and free fat graft (FFG). An autologous FDFG is a material used in plastic surgery and oncoplastic breast surgery that is ideal for immediate volume replacement after partial mastectomy because of its easy availability and minimal invasion of the donor site; however, immunohistochemical findings and survival procedures have not yet been reported. METHODS: An experimental protocol using a unique animal model was designed for the present study. The expression of vascular endothelial growth factor (VEGF) was measured in FDFGs and FFGs implanted onto the pectoral major muscle of Wistar rats. Thirty Wistar rats were divided into two groups and postoperatively 1, 2, 4, 8, and 16 weeks (POW1, 2, 4, 8, 16). Six samples from three rats in each group were used as control samples (POW0). RESULTS: The thickness of the implanted FDFG was not significantly different from the control sample at POW1, 2, 4, 8, and 16 between FDFG and FFG group; however, the thickness at POW8 and 16 was significantly lesser in the FFG group than in the control samples. The average proportion of fatty tissue to whole tissue ranged from 34.2 to 48.6 % in the FDFG group and from 57.2 to 76.7 % in the FFG group during the observation period; however, there was no significant difference in the proportion of fatty tissue between these two groups. There were no significant differences between the average number of VEGF-positive cells in the FDFG group and the FFG group at POW1, 2, 4, 8, and 16. The average number of TUNEL-positive cells in the early period at POW1 was significantly lower in the FDFG group than in the FFG group. CONCLUSIONS: This rat model was useful for investigating the mechanisms of angiogenesis, apoptosis, structure maintenance, and fibromatous changes. From the present experimental study, we believe that FDFG is one of the most convenient materials currently available to repair small defects at the time of BCS even in the clinical field.

Delta-like 1 homolog (DLK1) inhibits proliferation and myotube formation of avian QM7 myoblasts.

Delta-like 1 homolog (DLK1) has been implicated as an important regulator in mammalian muscle development. Our previous studies showed that different alternative splicing isoforms have distinct functions in the regulation of myogenesis in mice. Unlike most mammals, including mice, pigs, cattle, and sheep, DLK1 mRNA for avian species has a single form without alternative splicing. In the current study, we have used QM7 cells, a quail myoblast, to study the role of DLK1 in the regulation of avian myogenesis. Overexpression of DLK1 inhibited myogenesis with a lower fusion rate and thinner myotube compared to the control QM7 cells. Comparison of relative levels of protein and mRNA showed down-regulation of PAX7, MYOG, and MHC, and up-regulation of MYOD by DLK1, suggesting that quail DLK1 inhibits myogenesis at later stages of myogenic differentiation and myotube formation. DLK1 reduced the QM7 cell growth rate which is accompanied by a lower percentage of bromodeoxyuridine positive cells, indicating an inhibitory role of DLK1 in proliferation. During the early post-hatch ages, the relatively slower increase in the amount of total DNA mass in breast muscle of the heavy weight quail line, that has been selected for over 40 generations, could be partially explained by the higher expression of DLK1 compared to the control quail. Taken together, DLK1 inhibits myogenic differentiation and proliferation by regulating the expression levels of myogenic factors in quail. In addition, the regulation of expression level and cleavage of full-length DLK1 may be important factors for regulating myogenesis in quail having no splicing variants of DLK1.

The effects of intraperitoneal clenbuterol injection on protein degradation and myostatin expression differ between the sartorius and pectoral muscles of neonatal chicks.

The purpose of this study was to investigate the effects of injection of the ß2-adrenergic receptor agonist clenbuterol on the skeletal muscles of neonatal chicks (Gallus gallus domesticus). One-day-old chicks were randomly divided into four groups and given a single intraperitoneal injection of clenbuterol (0.01, 0.1, or 1mg/kg) or phosphate-buffered saline. Twenty-four hours after the injection, the sartorius muscles (which consist of both slow- and fast-twitch fibers) of chicks that received 0.01 or 0.1mg/kg clenbuterol were significantly heavier than those of controls, while there were no between-group differences in the weight of the pectoral muscles, which consist of only fast-twitch fibers. Muscle free N(t)-methylhistidine, regarded as an index of myofibrillar proteolysis, was decreased in the sartorius muscle of the clenbuterol-injected chicks, while it was not affected in the pectoral muscles. In the sartorius muscle of the clenbuterol-injected chicks, myostatin and atrogin-1/MAFbx mRNA expressions were decreased, while insulin-like growth factor-I was unaffected. These observations suggested, in 1-day-old chicks, clenbuterol might increase mass of the sartorius muscle by decreasing myostatin gene expression and protein degradation.

The effect of nutritional status on myogenic gene expression of satellite cells derived from different muscle types.

Satellite cells (SC) are a multipotential stem cell population responsible for facilitating posthatch muscle fiber hypertrophy. The proliferation and differentiation of SC is sensitive to nutritional regimen, and the SC response to nutrition varies depending upon their muscle type of origin. The objective of the current study was to determine the effect of altering protein synthesis on the expression of several key genes regulating SC activity and the effect of muscle type. Satellite cells isolated from the fast glycolytic pectoralis major and the fast oxidative and glycolytic biceps femoris were studied. These genes included the myogenic regulatory factors myogenic determination factor 1 (MyoD) and myogenin, the cell-membrane associated proteoglycans syndecan-4 and glypican-1, the extracellular matrix proteoglycan decorin, and the transcription factor paired box 7. Protein synthesis potential varied by the concentration of the sulfur amino acids Met and Cys during SC proliferation and differentiation. The SC were cultured and treated with 1 of 6 Met/Cys concentrations: 60/192, 30/96 (control), 7.5/24, 3.0/9.6, 1.0/3.2, or 0/0 mg/L. A consistent pattern of gene expression emerged following Met/Cys manipulation as increasing reductions in mRNA expression for all genes were observed as Met/Cys concentration decreased, whereas increased Met/Cys concentration caused either no change or had a small negative effect on mRNA expression. Reduced paired box 7 expression would limit myogenic specification of SC, whereas decreased myogenic regulatory factor expression would affect subsequent myogenic development of the SC. Decreased levels of decorin affect SC response to growth factors like myostatin and transforming growth factor ß, and extracellular matrix organization. These data highlight the importance of nutrition on the expression of genes critical for satellite cell activation, proliferation and differentiation, and growth factor signal transduction.

Retrograde migration of pectoral girdle muscle precursors depends on CXCR4/SDF-1 signaling.

In vertebrates, muscles of the pectoral girdle connect the forelimbs with the thorax. During development, the myogenic precursor cells migrate from the somites into the limb buds. Whereas most of the myogenic precursors remain in the limb bud to form the forelimb muscles, several cells migrate back toward the trunk to give rise to the superficial pectoral girdle muscles, such as the large pectoral muscle, the latissimus dorsi and the deltoid. Recently, this developing mode has been referred to as the "In-Out" mechanism. The present study focuses on the mechanisms of the "In-Out" migration during formation of the pectoral girdle muscles. Combining in ovo electroporation, tissue slice-cultures and confocal laser scanning microscopy, we visualize live in detail the retrograde migration of myogenic precursors from the forelimb bud into the trunk region by live imaging. Furthermore, we present for the first time evidence for the involvement of the chemokine receptor CXCR4 and its ligand SDF-1 during these processes. After microsurgical implantations of CXCR4 inhibitor beads in the proximal forelimb region of chicken embryos, we demonstrate with the aid of in situ hybridization and live-cell imaging that CXCR4/SDF-1 signaling is crucial for the retrograde migration of pectoral girdle muscle precursors. Moreover, we analyzed the MyoD expression in CXCR4-mutant mouse embryos and observed a considerable decrease in pectoral girdle musculature. We thus demonstrate the importance of the CXCR4/SDF-1 axis for the pectoral girdle muscle formation in avians and mammals.

Highlights in the minimally invasive treatment of SUI in women.

OBJECTIVE: Treatment of stress urinary incontinence consists of a wide range of options, from conservative therapies like lifestyle changes, medication, pelvic floor muscles exercises, electro-stimulation, to minimally invasive procedures--injection of collagen, suburethral slings TVT/TOT and last but not least, invasive surgical treatment reserved for recurrent and complex cases. Among the latest minimally invasive procedures reported in literature, the injection of intra-and perisphincterian of autologous stem cell (mioblasts and/or mature fibroblasts grown and multiplied in the laboratory from biopsy samples taken from the pectoralis muscles). MATERIAL AND METHOD: On October 18, 2010, in 'Fundeni' Clinical Institute of Uronephrology and Renal Transplantation was performed the first stem cell implantation procedure in the urethral sphincter, in Romania. RESULTS: Assessment at 6 weeks, the quality of life questionnaires, micturition diary and clinical examination revealed a stunning decrease of urine loss from 6 pads/day at one per day, which significantly improved the patient's quality of life. CONCLUSIONS: Stem-cell-mioblasts therapy may represent in the future an every-day intervention in the urologist's armamentarium. The effectiveness of this treatment can change the course of therapy and last but not least, the accessibility to urological evaluation of patients with stress urinary incontinence. Clinical and urodynamic evaluations will continue and will be future scientific topics.

Effects of monochromatic light on developmental changes in satellite cell population of pectoral muscle in broilers during early posthatch period.

To investigate the effects of various monochromatic lights on early posthatch changes in satellite cell mitotic activity of pectoral muscle, a total of 416 newly hatched broilers were exposed to blue light (BL), green light (GL), red light (RL), and white light (WL) by light emitting diode system for 3 weeks, respectively. Both, in culture and in vivo studies showed that after hatching, the relative number of satellite cells altered in correlation. The enhancement of satellite cell mitotic activity peaked at post-hatching day (P) 3 and then declined with age concomitantly with the rise in satellite cell differentiation and reduction of satellite cell proliferation. These alterations became more obvious in GL than in RL. The data suggested that early posthatch changes in satellite cell population of broilers occurred through the two different processes, i.e., cellular generation (before P3) and cellular degeneration (after P3). GL promoted significantly the broiler satellite cells to proliferate before P3 and to differentiate after P3. In addition, the circulating insulin-like growth factor-I (IGF-I) levels were higher in GL and BL groups versus WL and RL groups at P3 and P5 indicating that IGF-I plays a central role for GL illumination promoting broiler satellite cell myogenic processes during early posthatch stages.

The influence of age on maternal inheritance of breast muscle morphology in turkeys.

It was apparent in previous studies at our institution using turkeys that measurements of muscle fibers and extracellular spacing were not adequate to explain what was observed in entire pectoralis major muscle sections. A rating system was developed in which muscle sections were rated from 1 (little extracellular matrix and indistinct muscle fibers) to 5 (large extracellular space and distinct muscle fibers). Maternal inheritance was observed at 16 wk of age but not at 8 or 20 wk of age. The purpose of the current study was to determine the effect of age on maternal inheritance. A line (F) selected long-term for increased 16-wk BW, its randombred control (RBC2), and reciprocal crosses between them were compared from 8 through 18 wk of age. Samples of pectoralis major muscle were obtained in a manner to avoid muscle contraction. After being fixed and cross-sectioned, the muscle samples were stained with hematoxylin and eosin and rated by 4 individuals. No significant difference among genetic groups was observed in scores at 8 wk of age. At 10 wk of age, the F line had lower scores than the other genetic groups. Maternal inheritance was suggested at 12 wk of age. The scores for RBC2 were higher than those for F, whereas the F x RBC2 cross did not differ from the pure RBC2 line score at this age. Although the RBC2 x F scores were higher than the pure F-line scores at 12 wk, they were lower than those of the F x RBC2 crosses. From 14 through 18 wk of age, the scores for the RBC2 line were higher than those for the F line and the maternal inheritance was absolute because the value for the individual crosses did not differ from that of the maternal parent. Based on the results, the type of mating used to produce commercial turkeys would have a major effect on breast muscle morphology from 12 through 18 wk of age.

The pectoral fascia: anatomical and histological study.

AIM: Analysis of the pectoral fascia from a macroscopic and histological point of view. RESULTS: The pectoral fascia appears as a thin collagen layer (mean thickness of 297 microm) formed by undulated collagen fibres and many elastic fibres, within which small nerves are highlighted. Numerous septa detach from its internal surface, creating an intimate connection between the fascia and the pectoralis major muscle. DISCUSSION: The pectoral fascia and the pectoralis major muscle should be considered together, given that the anatomical base is effectively a myofascial unit, term that defines the muscles and the fascia of a specific region that have a precise functional organization. The capacity of force transmission between the inferior and superior limbs needs to be attributed to this entire myofascial complex. We hypothesize that the superficial, large muscles of the trunk developed inside the superficial layer of the deep fascia to enhance modulation of tension transmission between the different segments of the body.

Extracellular matrix proteoglycan decorin-mediated myogenic satellite cell responsiveness to transforming growth factor-beta1 during cell proliferation and differentiation Decorin and transforming growth factor-beta1 in satellite cells.

Transforming growth factor-beta1 (TGF-beta1) is a potent inhibitor of muscle cell proliferation and differentiation. Decorin, a small proteoglycan in the extracellular matrix, binds to TGF-beta1 and modulates the activity of TGF-beta1 during muscle cell growth and development. However, its interaction with TGF-beta1 and involvement in myogenesis is not well characterized. In the present study, chicken myogenic satellite cells, myogenic precursors for muscle growth and repair, were isolated from the pectoralis major muscle and used to investigate the biological function of TGF-beta1 and decorin during myogenesis. The over-expression of decorin in satellite cells significantly increased cell proliferation, compared to the control cells. Consistent with this result, reducing decorin expression decreased cell proliferation, which suggests a decorin-mediated mechanism is involved in the regulation of myogenic satellite cell proliferation. Satellite cells over-expressing decorin were less sensitive to TGF-beta1 during proliferation, which indicates that decorin may sequester TGF-beta1 leading to increased proliferation. During satellite cell differentiation, the over-expression of decorin induced differentiation by increasing the muscle specific creatine kinase concentration. However, the addition of TGF-beta1 diminished decorin-mediated cell responsiveness to TGF-beta1 during differentiation. Taken together, these results suggest that decorin induces myogenic satellite cell proliferation and differentiation by regulating cellular responsiveness to TGF-beta1. An alternative TGF-beta1-independent pathway may be involved in the regulation of satellite cells by decorin.

Pax7 reveals a greater frequency and concentration of satellite cells at the ends of growing skeletal muscle fibers.

The main sites of longitudinal growth in skeletal muscle are the ends of the fibers. This study tests the hypothesis that satellite cells (SCs) are at a greater frequency (#SC nuclei/all nuclei within basal laminae) and concentration (closer together) within growing fiber ends of posthatch chicken pectoralis. SCs were localized by their Pax7 expression, and fiber ends were identified by their retention of neonatal myosin heavy chains and small cross-sectional profiles. Whereas SC frequency decreased from about 20% at 9 days posthatch to <5% at 115 days, fiber ends retained a frequency of approximately 16%. Calculated mean area of sarcolemma per SC revealed higher concentrations of SCs at fiber ends. There was also a strong inverse correlation between SC frequency and fiber profile cross-sectional size throughout development. This study suggests that SCs at fiber ends play a key role in the longitudinal growth of muscle fibers, and that fiber profile size may impact SC distribution.