The effect of nutritional status on myogenic satellite cell proliferation and differentiation

Advances and Challenges in Cell Biology for Cultured Meat

Cultured meat is an emerging biotechnology that aims to produce meat from animal cell culture, rather than from the raising and slaughtering of livestock, on environmental and animal welfare grounds. The detailed understanding and accurate manipulation of cell biology are critical to the design of cultured meat bioprocesses. Recent years have seen significant interest in this field, with numerous scientific and commercial breakthroughs. Nevertheless, these technologies remain at a nascent stage, and myriad challenges remain, spanning the entire bioprocess. From a cell biological perspective, these include the identification of suitable starting cell types, tuning of proliferation and differentiation conditions, and optimization of cell-biomaterial interactions to create nutritious, enticing foods. Here, we discuss the key advances and outstanding challenges in cultured meat, with a particular focus on cell biology, and argue that solving the remaining bottlenecks in a cost-effective, scalable fashion will require coordinated, concerted scientific efforts. Success will also require solutions to nonscientific challenges, including regulatory approval, consumer acceptance, and market feasibility. However, if these can be overcome, cultured meat technologies can revolutionize our approach to food.

The effect of protease on growth performance, nutrient digestibility, and expression of growth-related genes and amino acid transporters in broilers

During the course of this trial, our team assessed the influence of protease upon the growth performance, the nutrient digestibility, and the expression of growth-related genes and amino acid transporters within the liver, muscle, and small intestines of broilers. During the first step, our team allocated 600 broilers into four dietary treatments for a period of 35 days in order to measure the growth performance and nutrient digestibility of the broilers selected. The separate treatments contained 10 replicates (15 birds per replicate). The treatments were composed of: 1) CON, basal diet; 2) T1, basal diet + 0.03% protease; 3) T2, basal diet + 0.06% protease; and 4) T3, basal diet + 0.09% protease. Next, the broiler chick sample tissue was harvested from the CON and T3 groups in order to conduct gene expression analysis following the feeding trials the broilers underwent. Our team discovered that the broilers fed protease diets possessed increased body weight and an average daily gain, but conversely, had lower feed conversion ratios when their dietary protease levels increased from 0% to 0.09% (p < 0.05). Additionally, significant linear improvements were identified among the nutrient digestibility of dry matter, crude protein, energy, and amino acids within broilers supplied with protease diets when contrasted and compared with broilers supplied with the basal diet (p < 0.05). In addition, the gene expression of the genes IGF1, IGF2, GH, and LEP in the liver, and the genes MYOD1 and MYOG in the breast muscles, was significantly increased after broilers were fed with a protease diet as compared to broilers that subsisted on a basal diet (p < 0.05). Protease supplementation also raised the expression levels within these amino acid transporters: SCL6A19, SLC7A1, SLC7A7, SLC7A2, SLC7A6, SLC7A9, and SLC15A1, located in the small intestine, when compared to the basal diet (p < 0.05). Our results suggest that protease supplementation in their diet improved the growth performance of broilers via an increase in the expression growth-related genes within broiler liver and muscle tissue. In addition, protease supplementation enhanced broiler digestibility via the upregulation of amino acid transporter expression within the small intestine.

The effect of nutrient restriction and syndecan-4 or glypican-1 knockdown on the differentiation of turkey pectoralis major satellite cells differing in age and growth selection

Skeletal muscle growth is mediated by the proliferation and differentiation of satellite cells, whose activity is affected by both nutrition and the expression of syndecan-4 and glypican-1. Previous research has not addressed if there is an interactive effect of nutrition with the expression of syndecan-4 and glypican-1. Thus, the objective of the current study was to determine if the response of satellite cells to nutrient restriction was altered by syndecan-4 or glypican-1 knockdown and if age and growth selection are factors. Satellite cells were isolated from pectoralis major muscle of 1-day, 7-wk, and 16-wk-old turkeys selected for increased 16-wk body weight (F line) and the randombred control (RBC2) line from which the F line was selected. Syndecan-4 or glypican-1 expression was knocked down in both lines using small interfering RNAs along with nutrient restriction of 0 or 20% of the standard cell culture medium either applied during proliferation with subsequent normal differentiation medium (RN) or during differentiation with preceding normal proliferation medium (NR). For both lines, nutrient restriction and syndecan-4 or glypican-1 knockdown had an independent and additive effect on satellite cell differentiation at 72 h of differentiation except for 1 d satellite cells. The 1 d satellite cell differentiation was increased by RN treatment, but when combined with syndecan-4 or glypican-1 knockdown, the increase in differentiation was negated. At 48 h of differentiation, syndecan-4 knockdown in 7 and 16 wk satellite cells and glypican-1 knockdown in 7 wk cells cancelled the effect of the RN treatment, but enhanced the effect of NR treatment at 24 h of differentiation. Growth selection had little effect on the interaction between nutrient restriction and syndecan-4 or glypican-1 knockdown. Taken together, these data demonstrate that the satellite cell response to nutrition is dependent on the expression of syndecan-4 and glypican-1 in an age-dependent manner with growth selection having little impact.

Nutrient restriction and migration of turkey satellite cells

Post hatch muscle growth and the repair or regeneration of muscle after myofiber injury is mediated by satellite cells. Satellite cells proliferate, migrate, differentiate, and fuse with growing or regenerating myofibers. The proliferation and differentiation of satellite cells are affected by nutrition, but it is unknown how nutrition impacts satellite cell migration. The objective of the study was to determine the effect of a nutrient restriction on satellite cell migration. Satellite cells from the pectoralis major muscle of 1 and 49-day-old Randombred Control Line 2 turkeys were grown in culture, and migration was measured using a wound healing assay. Nutrient restrictions of 0, 5, 10, and 20% of the standard culture medium were applied starting immediately after scratch or 24 h prior to scratch. Nutrient restrictions of 5 and 20% increased 1 D satellite cell migration at 6 h post scratch compared to 1 D satellite cells with standard culture medium but had no effect after 12 h post scratch. Nutrient restrictions started 24 h prior to scratch increased 1 D satellite cell migration at 6 and 12 h post scratch compared to nutrient restrictions started immediately after scratch. The migration of 49 D satellite cells was not affected by the percentage or timing of the nutrient restriction. These data suggest that nutrition has only a minor effect on the migration of turkey pectoralis major muscle satellite cells. Therefore, the influence of nutrition on satellite cell migration is likely not an important factor for evaluating poultry diet formulations to optimize muscle growth and structure for improved meat protein and fat content as well as meat texture.

TRIENNIAL GROWTH SYMPOSIUM: THE NUTRITION OF MUSCLE GROWTH: Impacts of nutrition on the proliferation and differentiation of satellite cells in livestock species1,2

Nutrition and other external factors are known to have a marked effect on growth of skeletal muscle, modulated, at least in part, through effects on satellite cells. Satellite cells and their embryonic precursors play an integral role in both prenatal and postnatal skeletal muscle growth of mammals. Changes in maternal nutrition can impact embryonic muscle progenitor cells which ultimately impacts both prenatal and postnatal skeletal muscle development. Satellite cells are important in postnatal skeletal muscle growth as they support the hypertrophy of existing myofibers. Hypertrophy of existing fibers is the only mechanism of postnatal muscle growth because muscle fiber number is fixed at birth and fiber nuclei have exited the cell cycle. Because fiber nuclei do not divide, additional nuclei required for hypertrophy must be acquired from satellite cells. To date, little research has aimed at determining whether nutrition directly impacts satellite cell populations within skeletal muscle of livestock species. However, it is well established that nutrition alters circulating concentrations of various growth factors such as insulin-like growth factor 1, epidermal growth factor, hepatocyte growth factor, and fibroblast growth factor. Each of these different growth factors impacts satellite cell proliferation and/or activation, indicating that nutrition likely plays a large role in skeletal muscle growth through impacting the satellite cell pool in both prenatal and postnatal growth. The relationship among nutrition, growth factors, and satellite cells relative to skeletal muscle growth is an important area of research that warrants further consideration.

Muscle weakness: Understanding the principles of myopathy and neuropathy in the critically ill patient and the management options

Myo-neuropathy of the critically ill patient is a difficult nosological entity to understand and manage. It appears soon after injury, and it is estimated that 20-30% of patients admitted to Intensive Care Units will develop it in some degree. Although muscular and nervous involvement are related, the former has a better prognosis. Myo-neuropathy associates to more morbidity, longer stay in Intensive Care Unit and in hospital, and also to higher costs and mortality. It is considered part of the main determinants of the new entities: the Chronic Critical Patient and the Post Intensive Care Syndrome. This update focuses on aetiology, pathophysiology, diagnosis and strategies that can prevent, alleviate and/or improve muscle (or muscle-nerve) weakness.

Evaluation of different dietary alterations in their ability to mitigate the incidence and severity of woody breast and white striping in commercial male broilers

The following study was conducted to define how multiple nutritional strategies affect broiler performance, meat yield, and the presence and severity of white striping (WS) and woody breast (WB) in high-yielding broilers. Relative to a commercial set of reference broiler diets (Commercial reference diet; Trt 1) that were fed in a 4-phase program, the following nutritional strategies were investigated: increasing the ratio of digestible arginine: digestible lysine (dArg: dLys ranged from 113 to 126; Trt 2), supplementing Trt 1 with 94.4 mg vitamin C/kg feed (Trt 3), doubling the vitamin pack inclusion rate (Trt 4), reducing the digestible amino acid density (dAA) of only the grower phase by 15% and feeding the same Trt 1 starter, finisher, and withdraw diets (Trt 5), and combining the 4 strategies just mentioned (Trt 6). There was no difference in performance at the end of the starter phase (P = 0.066); however, at the end of the grower and finisher phases, feeding lower dAA grower diets suppressed BW (Trts 5 and 6; P < 0.001) and increased FCR. Differences in performance amongst all treatments disappeared at day 49 (P = 0.220). No differences were observed in average breast weight (P = 0.188); however, breast yield (as a % of live weight) was greatest for Trt 1 and least for Trt 6 (P = 0.041). The WB score dropped from 1.83 in Trt 1 to 1.49, 1.27, 1.74, 1.53, and 1.43 in treatments 2 to 6, respectively (P = 0.018). These changes were the result of a shift in WB score, where the WB class that contained scores of 2 and 3 shifted from 61.3% in Trt 1 to 49.3, 35.9, 60.0, 50.8, and 38.7 in treatments 2 to 6, respectively. Given the FCR, breast weight data and the fact that high WB scores result in a devaluation of breast meat, feeding a higher ratio of dArg: dLys, higher vitamin C, or lower dAA in the grower phase results in better breast meat quality and value.

Early posthatch thermal stress affects breast muscle development and satellite cell growth and characteristics in broilers

Heat or cold stress, can disrupt well-being and physiological responses in birds. This study aimed to elucidate the effects of continuous heat exposure in the first 2 wk of age on muscle development in broilers, with an emphasis on the pectoralis muscle satellite cell population. Chicks were reared for 13 d under either commercial conditions or a temperature regime that was 5°C higher. Body and muscle weights, as well as absolute muscle growth were lower in heat-exposed chicks from d 6 onward. The number of satellite cells derived from the experimental chicks was higher in the heat-treated group on d 3 but lower on d 8 and 13 compared to controls. This was reflected in a lower number of myonuclei expressing proliferating nuclear cell antigen in cross sections of pectoralis major muscle sampled on d 8. However, a TUNEL assay revealed similar cell survival in both groups. Mean myofiber diameter and distribution were lower in muscle sections sampled on d 8 and 13 in heat-treated versus control group, suggesting that the lower muscle growth is due to changes in muscle hypertrophy. Oil-Red O staining showed a higher number of satellite cells with lipids in the heat-treated compared to the control group on these days. Moreover, lipid deposition was observed in pectoralis muscle cross sections derived from the heat-treated chicks on d 13, whereas the controls barely exhibited any lipid staining. The gene and protein expression levels of CCAAT/enhancer binding protein β in pectoralis muscle from the heat-treated group were significantly higher on d 13 than in controls, while myogenin levels were similar. The results suggest high sensitivity of muscle progenitor cells in the early posthatch period at a time when they are highly active, to chronic heat exposure, leading to impaired myogenicity of the satellite cells and increased fat deposition.

Potential Benefits of Ameliorating Metabolic and Nutritional Abnormalities in People With Profound Developmental Disabilities

Background:

People with profound developmental disabilities have some of the most severe neurological impairments seen in society, have accelerated mortality due to huge medical challenges, and yet are often excluded from scientific studies. They actually have at least 2 layers of conditions: (1) the original disability and (2) multiple under-recognized and underexplored metabolic and nutritional imbalances involving minerals (calcium, zinc, and selenium), amino acids (taurine, tryptophan), fatty acids (linoleic acid, docosahexaenoic acid, arachidonic acid, adrenic acid, Mead acid, plasmalogens), carnitine, hormones (insulinlike growth factor 1), measures of oxidative stress, and likely other substances and systems.

Summary:

This review provides the first list of metabolic and nutritional abnormalities commonly found in people with profound developmental disabilities and, based on the quality of life effects of similar abnormalities in neurotypical people, indicates the potential effects of these abnormalities in this population which often cannot communicate symptoms.

Key messages:

We propose that improved understanding and management of these disturbed mechanisms would enhance the quality of life of people with profound developmental disabilities. Such insights may also apply to people with other conditions associated with disability, including some diseases requiring stem cell implantation and living in microgravity.

Methionine concentration in the pre-starter diet: its effect on broiler breast muscle development

The effect of feeding diets of variable methionine concentration on breast muscle development was assessed in Ross 308 broiler chicks. Four isonitrogenous and isoenergetic starter diets were formulated to contain 7.8, 5.9, 4.6, and 3.4 g methionine/kg diet, and were provided for the first 7 days post-hatch. At 7 days of age all birds were placed on an industry standard starter diet with 5.9 g methionine/kg diet until 14 days, and then provided standard broiler grower (until 28 days) and finisher (until 42 days) diets. Birds were weighed periodically throughout the study and feed intake and feed conversion ratio were determined. Ten birds per treatment were sacrificed and weighed on 0, 1, 4, 7, 14, 21, 28, 35, and 42 days. The pectoralis major (breast muscle) was then removed from the carcass and weighed. Samples of breast muscle were collected for genetic and histological analysis. Expression of the myogenic marker genes, myogenic differentiation factor 1 and myogenin, which regulate satellite cell activity, and the adipogenic marker gene, peroxisome proliferator-activated receptor gamma (PPARγ), was measured. Histological assessment of breast muscle morphology and fat deposition morphology was also performed. No effect of dietary treatment was observed on body or breast muscle weight, feed intake or feed conversion ratio. Marker gene expression was also similar in all treatment groups, except for PPARγ. Significantly higher expression of PPARγ was observed at 0 days in the 5.9 g methionine/kg diet treatment, before dietary treatments were provided. Expression of PPARγ did not differ among treatment groups on any subsequent day. Methionine dietary treatment had no effect on the morphological structure of the breast muscle, or intramuscular fat deposition. These results suggest that under the conditions of this study, satellite cell activity in the early post-hatch chick, and subsequent muscle development, were not responsive to the variable methionine manipulations tested in the pre-starter period.

Relationship of Skeletal Muscle Development and Growth to Breast Muscle Myopathies: A Review

Selection in meat-type birds has focused on growth rate, muscling, and feed conversion. These strategies have made substantial improvements but have affected muscle structure, repair mechanisms, and meat quality, especially in the breast muscle. The increase in muscle fiber diameters has reduced available connective tissue spacing, reduced blood supply, and altered muscle metabolism in the breast muscle. These changes have increased muscle fiber degeneration and necrosis but have limited muscle repair mechanisms mediated by the adult myoblast (satellite cell) population of cells, likely resulting in the onset of myopathies. This review focuses on muscle growth mechanisms and how changes in the cellular development of the breast muscle may be associated with breast muscle myopathies occurring in meat-type birds.

Potential Role of Omega-3 Fatty Acids on the Myogenic Program of Satellite Cells

Skeletal muscle loss is associated with aging as well as pathological conditions. Satellite cells (SCs) play an important role in muscle regeneration. Omega-3 fatty acids are widely studied in a variety of muscle wasting diseases; however, little is known about their impact on skeletal muscle regeneration. The aim of this review is to evaluate studies examining the effect of omega-3 fatty acids, α-linolenic acid, eicosapentaenoic acid, and docosahexaenoic acid on the regulation of SC proliferation and differentiation. This review highlights mechanisms by which omega-3 fatty acids may modulate the myogenic program of the stem cell population within skeletal muscles and identifies considerations for future studies. It is proposed that minimally three myogenic transcriptional regulatory factors, paired box 7 (Pax7), myogenic differentiation 1 protein, and myogenin, should be measured to confirm the stage of SCs within the myogenic program affected by omega-3 fatty acids.

Temperature effect on proliferation and differentiation of satellite cells from turkeys with different growth rates

Poultry selected for growth have an inefficient thermoregulatory system and are more sensitive to temperature extremes. Satellite cells are precursors to skeletal muscle and mediate all posthatch muscle growth. Their physiological functions are affected by temperature. The objective of the current study was to determine how temperature affects satellite cells isolated from the pectoralis major (p. major) muscle (breast muscle) of turkeys selected for increased 16 wk body weight (F line) in comparison to a randombred control line (RBC2) from which the F line originated. Pectoralis major muscle satellite cells were thermally challenged by culturing between 33°C and 43°C to analyze the effects of cold and heat on proliferation and differentiation as compared to control temperature of 38°C. Expression levels of myogenic regulatory factors: myogenic differentiation factor 1 (MYOD1) and myogenin (MYOG) were quantified by quantitative polymerase chain reaction (qPCR). At all sampling times, proliferation increased at a linear rate across temperature in both the RBC2 and F lines. Differentiation also increased at a linear rate across temperature from 33 to 41°C at all sampling times in both the F and RBC2 lines. Satellite cells isolated from F line turkeys were more sensitive to both hot and cold temperatures as proliferation and differentiation increased to a greater extent across temperature (33 to 43°C) when compared with the RBC2 line. Expression of MYOD1 and MYOG increased as temperatures increased from 33 to 41°C at all sampling times in both the F and RBC2 lines. These results demonstrate that satellite cell function is sensitive to both cold and hot temperatures and p. major muscle satellite cells from F line turkeys are more sensitive to temperature extremes than RBC2 satellite cells.

Regulation of satellite cell function in sarcopenia

The mechanisms contributing to sarcopenia include reduced satellite cell (myogenic stem cell) function that is impacted by the environment (niche) of these cells. Satellite cell function is affected by oxidative stress, which is elevated in aged muscles, and this along with changes in largely unknown systemic factors, likely contribute to the manner in which satellite cells respond to stressors such as exercise, disuse, or rehabilitation in sarcopenic muscles. Nutritional intervention provides one therapeutic strategy to improve the satellite cell niche and systemic factors, with the goal of improving satellite cell function in aging muscles. Although many elderly persons consume various nutraceuticals with the hope of improving health, most of these compounds have not been thoroughly tested, and the impacts that they might have on sarcopenia and satellite cell function are not clear. This review discusses data pertaining to the satellite cell responses and function in aging skeletal muscle, and the impact that three compounds: resveratrol, green tea catechins, and β-Hydroxy-β-methylbutyrate have on regulating satellite cell function and therefore contributing to reducing sarcopenia or improving muscle mass after disuse in aging. The data suggest that these nutraceutical compounds improve satellite cell function during rehabilitative loading in animal models of aging after disuse (i.e., muscle regeneration). While these compounds have not been rigorously tested in humans, the data from animal models of aging provide a strong basis for conducting additional focused work to determine if these or other nutraceuticals can offset the muscle losses, or improve regeneration in sarcopenic muscles of older humans via improving satellite cell function.

Effect of the timing of posthatch feed restrictions on the deposition of fat during broiler breast muscle development

The effect of the timing of posthatch feed restriction on adipose deposition and adipogenic gene expression in the broiler pectoralis major muscle was studied by applying a 20% feed restriction either the first or second week after hatch. Broiler chicks at hatch were divided into a full-fed (control) group and a 20% feed restriction group. The expression of adipogenic genes, peroxisome proliferator-activated receptor gamma (PPARγ), and CCAAT/enhancer-binding protein alpha (C/EBPα) were measured. The expression of both PPARγ and C/EBPα was affected by the wk 1 feed restriction with expression significantly increased during the first week posthatch. The deposition of fat within the pectoralis major muscle was affected by the timing of the feed restriction. Extensive fat depots were present by 27 d of age in the pectoralis major muscle of the wk 1 restricted group compared with the control. Fat deposition was eliminated when the 20% feed restriction occurred in wk 2. Taken together, these results demonstrate that the timing of early posthatch feed restrictions in chicks is critical in the deposition of fat in the pectoralis major muscle and expression of adipogenic genes.

Effect of the timing of posthatch feed restrictions on broiler breast muscle development and muscle transcriptional regulatory factor gene expression

The effect of the timing of an immediate posthatch feed restriction on broiler pectoralis major muscle development was studied by applying a 20% feed restriction either the first or second week after hatch. Pectoralis major muscle morphological structure and the expression of the myogenic transcriptional regulatory factors, myogenic determination factor 1 (MyoD), myogenic regulatory factor 4 (MRF4), and myogenin, were measured. Broiler chicks at hatch were divided into a full-fed (control) group and a 20% feed restriction treatment administered either the first or second week posthatch. At the end of the feed restriction, the chicks were placed on a full feed ad libitum diet with no further restrictions. Muscle fiber diameter and fiber bundle size of the pectoralis major muscle were smaller in the wk 1 restricted group than the control group by 7 d of age. By 15 d of age through the duration of the study, d 43, both endomysial and perimysial connective tissue spacing were diminished in the wk 1 feed-restricted group. The expression of MyoD, MRF4, and myogenin was affected by the wk 1 feed restriction. The expression of MyoD and MRF4 was significantly increased during the first week posthatch. Both of the genes have been shown to be expressed during proliferation especially MyoD, which is required for muscle cell proliferation. In contrast, myogenin expression was significantly decreased. Myogenin expression is required for differentiation to occur. The morphological changes and gene expression changes observed with the wk 1 feed restriction were eliminated by moving the 20% feed restriction to wk 2, which is after the period of maximal myogenic satellite cell mitotic activity. Taken together, these results demonstrate that the timing of early posthatch feed restrictions to chicks is critical for the morphological development of the pectoralis major muscle and the expression of genes required for muscle satellite cell proliferation and differentiation.

The effect of nutritional status and muscle fiber type on myogenic satellite cell fate and apoptosis

Satellite cells (SC) are multipotential stem cells that can be induced by nutrition to alter their cellular developmental fate, which may vary depending on their fiber type origin. The objective of the current study was to determine the effect of restricting protein synthesis on inducing adipogenic transdifferentiation and apoptosis of SC originating from fibers of the fast glycolytic pectoralis major (p. major) and fast oxidative and glycolytic biceps femoris (b. femoris) muscles of the chicken. The availability of the essential sulfur amino acids Met and Cys was restricted to regulate protein synthesis 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, 3/9.6, 1/3.2, or 0/0 mg/L. Reductions in Met/Cys concentrations from the control level resulted in increased lipid staining and expression of the adipogenic marker genes peroxisome proliferator-activated receptor gamma and stearoyl-CoA desaturase during differentiation in the p. major SC. Although b. femoris SC had increased lipid staining at lower Met/Cys concentrations, there was no increase in expression of either adipogenic gene. For both muscle types, SC Met/Cys, concentration above the control increased the expression of peroxisome proliferator-activated receptor gamma and stearoyl-CoA desaturase during differentiation. As Met/Cys concentration was decreased during proliferation, a dose-dependent decline in all apoptotic cells occurred except for early apoptotic cells in the p. major, which had no treatment effect (P < 0.05). During differentiation, decreasing Met/Cys concentration caused an increase in early apoptotic cells in both fiber types and no effect on late apoptotic cells except for an increase in the p. major 7.5/24 mg/L of Met/Cys treatment. In general, the viability of the SC was unaffected by the Met/Cys concentration except during proliferation in the p. major 0/0 mg/L of Met/Cys treatment, which increased SC viability. These data demonstrate the effect of nutrition on SC transdifferentiation to an adipogenic lineage and apoptosis, and the effect of fiber type on this response in an in vitro context.

The effect of nutritional status and myogenic satellite cell age on turkey satellite cell proliferation, differentiation, and expression of myogenic transcriptional regulatory factors and heparan sulfate proteoglycans syndecan-4 and glypican-1

Posthatch satellite cell mitotic activity is a critical component of muscle development and growth. Satellite cells are myogenic stem cells that can be induced by nutrition to follow other cellular developmental pathways, and whose mitotic activity declines with age. The objective of the current study was to determine the effect of restricting protein synthesis on the proliferation and differentiation, expression of myogenic transcriptional regulatory factors myogenic determination factor 1, myogenin, and myogenic regulatory factor 4, and expression of the heparan sulfate proteoglycans syndecan-4 and glypican-1 in satellite cells isolated from 1-d-, 7-wk-, and 16-wk-old turkey pectoralis major muscle (1 d, 7 wk, and 16 wk cells, respectively) by using variable concentrations of Met and Cys. Four Met concentrations-30 (control), 7.5, 3, or 0 mg/L with 3.2 mg/L of Cys per 1 mg/L of Met-were used for culture of satellite cells to determine the effect of nutrition and age on satellite cell behavior during proliferation and differentiation. Proliferation was reduced by lower Met and Cys concentrations in all ages at 96 h of proliferation. Differentiation was increased in the 1 d Met-restricted cells, whereas the 7 wk cells treated with 3 mg/L of Met had decreased differentiation. Reduced Met and Cys levels from the control did not significantly affect the 16 wk cells at 72 h of differentiation. However, medium with no Met or Cys suppressed differentiation at all ages. The expression of myogenic determination factor 1, myogenin, myogenic regulatory factor 4, syndecan-4, and glypican-1 was differentially affected by age and Met or Cys treatment. These data demonstrate the age-specific manner in which turkey pectoralis major muscle satellite cells respond to nutritional availability and the importance of defining optimal nutrition to maximize satellite cell proliferation and differentiation for subsequent muscle mass accretion.