Randombred Control Line Research Articles

Differential effects of temperature and mTOR and Wnt-planar cell polarity pathways on syndecan-4 and CD44 expression in growth-selected turkey satellite cell populations.

Satellite cells (SCs) comprise a heterogeneous population of muscle stem cells. Thermal stress during the first week after hatch alters proliferation, myogenesis, and adipogenesis of SCs of turkey pectoralis major (p. major) muscle via mechanistic target of rapamycin (mTOR) and wingless-type mouse mammary tumor virus integration site family/planar cell polarity (Wnt/PCP) pathways. Pivotal genes in mTOR and Wnt/PCP pathways are mTOR and frizzled-7 (Fzd7), respectively. The objective of this study was to determine the differential effects of thermal stress on SDC4 and CD44 expression in turkey p. major muscle SCs and how the expression of SDC4 and CD44 is modulated by the mTOR and Wnt/PCP pathways. Satellite cells were isolated from the p. major muscle of 1-week-old faster-growing modern-commercial (NC) turkeys and slower-growing historic Randombred Control Line 2 (RBC2) turkeys, and were challenged with hot (43°C) and cold (33°C) thermal stress for 72 h of proliferation followed by 48 h of differentiation. The NC line SCs were found to contain a lower proportion of SDC4 positive and CD44 negative (SDC4+CD44-) cells and a greater proportion of SDC4 negative and CD44 positive (SDC4-CD44+) cells compared to the RBC2 line at the control temperature (38°C) at both 72 h of proliferation and 48 h of differentiation. In general, at 72 h of proliferation, the proportion of SDC4+CD44- cells decreased with heat stress (43°C) and increased with cold stress (33°C) relative to the control temperature (38°C) in both lines, whereas the proportion of SDC4-CD44+ cells increased with heat stress and decreased with cold stress. In general, the expression of SDC4 and CD44 in the NC SCs showed greater response to both hot and cold thermal stress compared to the RBC2 cells. Knockdown of mTOR or Fzd7 expression increased the proportion of SDC4+CD44- cells while the proportion of SDC4-CD44+ cells decreased during differentiation with line differences being specific to treatment temperatures. Thus, differential composition of p. major muscle SCs in growth-selected commercial turkey may be resulted, in part, from the alteration in SDC4 and CD44 expression. Results indicate differential temperature sensitivity and mTOR and Wnt/PCP pathway responses of growth-selected SC populations and this may have long-lasting effect on muscle development and growth.

Transcriptome Response of Differentiating Muscle Satellite Cells to Thermal Challenge in Commercial Turkey.

Early muscle development involves the proliferation and differentiation of stem cells (satellite cells, SCs) in the mesoderm to form multinucleated myotubes that mature into muscle fibers and fiber bundles. Proliferation of SCs increases the number of cells available for muscle formation while simultaneously maintaining a population of cells for future response. Differentiation dramatically changes properties of the SCs and environmental stressors can have long lasting effects on muscle growth and physiology. This study was designed to characterize transcriptional changes induced in turkey SCs undergoing differentiation under thermal challenge. Satellite cells from the pectoralis major (p. major) muscle of 1-wk old commercial fast-growing birds (Nicholas turkey, NCT) and from a slower-growing research line (Randombred Control Line 2, RBC2) were proliferated for 72 h at 38 °C and then differentiated for 48 h at 33 °C (cold), 43 °C (hot) or 38 °C (control). Gene expression among thermal treatments and between turkey lines was examined by RNAseq to detect significant differentially expressed genes (DEGs). Cold treatment resulted in significant gene expression changes in the SCs from both turkey lines, with the primary effect being down regulation of the DEGs with overrepresentation of genes involved in regulation of skeletal muscle tissue regeneration and sarcomere organization. Heat stress increased expression of genes reported to regulate myoblast differentiation and survival and to promote cell adhesion particularly in the NCT line. Results suggest that growth selection in turkeys has altered the developmental potential of SCs in commercial birds to increase hypertrophic potential of the p. major muscle and sarcomere assembly. The biology of SCs may account for the distinctly different outcomes in response to thermal challenge on breast muscle growth, development, and structure of the turkey.

Thermal stress and selection for growth affect myogenic satellite cell lipid accumulation and adipogenic gene expression through mechanistic target of rapamycin pathway.

Satellite cells (SCs) are multipotential stem cells having the plasticity to convert to an adipogenic lineage in response to thermal stress during the period of peak mitotic activity (the first week after hatch in poultry). The mechanistic target of rapamycin (mTOR) pathway, which regulates cellular function and fate of SCs, is greatly altered by thermal stress in turkey pectoralis major muscle SCs. The objective of the present study was to determine the effects of thermal stress, selection for growth, and the role of the mTOR pathway on SC intracellular lipid accumulation and expression of adipogenic regulatory genes. These effects were analyzed using SCs isolated from the pectoralis major muscle of 1-wk-old modern faster-growing commercial turkey line (NC) selected for increased growth and breast muscle yield as compared with SCs of a historic slower-growing Randombred Control Line 2 (RBC2) turkey. Heat stress (43 °C) of SCs during proliferation increased intracellular lipid accumulation (P < 0.001), whereas cold stress (33 °C) showed an inhibitory effect (P < 0.001) in both lines. Knockdown of mTOR reduced the intracellular lipid accumulation (P < 0.001) and suppressed the expression of several adipogenic regulatory genes: peroxisome proliferator-activated receptor-γ (PPARγ; P < 0.001), CCAAT/enhancer-binding protein-β (C/EBPβ; P < 0.001), and neuropeptide-Y (NPY; P < 0.001) during both proliferation and differentiation. The NC line SCs showed fewer reductions in lipid accumulation compared with the RBC2 line independent of temperature. Both intracellular lipid accumulation (P < 0.001) and PPARγ expression (P < 0.001) were greater at 72 h of proliferation than at 48 h of differentiation in both the RBC2 and NC lines independent of temperature. Thus, hot and cold thermal stress affected intracellular lipid accumulation in the pectoralis major muscle SCs, in part, through the mTOR pathway in wea growth-dependent manner. Altered intracellular lipid accumulation could eventually affect intramuscular fat deposition, resulting in a long-lasting effect on the structure and protein to fat ratio of the poultry pectoralis major muscle.

Temperature and Growth Selection Effects on Proliferation, Differentiation, and Adipogenic Potential of Turkey Myogenic Satellite Cells Through Frizzled-7-Mediated Wnt Planar Cell Polarity Pathway.

Satellite cells (SCs) are a heterogeneous population of multipotential stem cells. During the first week after hatch, satellite cell function and fate are sensitive to temperature. Wingless-type mouse mammary tumor virus integration site family/planar cell polarity (Wnt/PCP) signaling pathway is significantly affected by thermal stress in turkey pectoralis major (p. major) muscle SCs. This pathway regulates the activity of SCs through a frizzled-7 (Fzd7) cell surface receptor and two intracellular effectors, rho-associated protein kinase (ROCK) and c-Jun. The objective of the present study was to determine the effects of thermal stress, growth selection, and the Fzd7-mediated Wnt/PCP pathway on proliferation, myogenic differentiation, lipid accumulation, and expression of myogenic and adipogenic regulatory genes. These effects were evaluated in SCs isolated from the p. major muscle of 1-week faster-growing modern commercial (NC) line of turkeys as compared to SCs of a slower-growing historic Randombred Control Line 2 (RBC2) turkey line. Heat stress (43°C) increased phosphorylation of both ROCK and c-Jun with greater increases observed in the RBC2 line. Cold stress (33°C) had an inhibitory effect on both ROCK and c-Jun phosphorylation with the NC line showing greater reductions. Knockdown of the expression of Fzd7 decreased proliferation, differentiation, and expression of myogenic regulatory genes: myoblast determination factor-1 and myogenin in both lines. Both lipid accumulation and expression of adipogenic regulatory genes: peroxisome proliferator-activated receptor-γ, CCAAT/enhancer-binding protein-β, and neuropeptide-Y were suppressed with the Fzd7 knockdown. The RBC2 line was more dependent on the Fzd7-mediated Wnt/PCP pathway for proliferation, differentiation, and lipid accumulation compared to the NC line. Thus, thermal stress may affect poultry breast muscle growth potential and protein to fat ratio by altering function and fate of SCs through the Fzd7-mediated Wnt/PCP pathway in a growth-dependent manner.

Thermal stress affects proliferation and differentiation of turkey satellite cells through the mTOR/S6K pathway in a growth-dependent manner.

Satellite cells (SCs) are stem cells responsible for post-hatch muscle growth through hypertrophy and in birds are sensitive to thermal stress during the first week after hatch. The mechanistic target of rapamycin (mTOR) signaling pathway, which is highly responsive to thermal stress in differentiating turkey pectoralis major (p. major) muscle SCs, regulates protein synthesis and the activities of SCs through a downstream effector, S6 kinase (S6K). The objectives of this study were: 1) to determine the effect of heat (43°C) and cold (33°C) stress on activity of the mTOR/S6K pathway in SCs isolated from the p. major muscle of one-week-old faster-growing modern commercial (NC) turkeys compared to those from slower-growing Randombred Control Line 2 (RBC2) turkeys, and 2) to assess the effect of mTOR knockdown on the proliferation, differentiation, and expression of myogenic regulatory factors of the SCs. Heat stress increased phosphorylation of both mTOR and S6K in both turkey lines, with greater increases observed in the RBC2 line. With cold stress, greater reductions in mTOR and S6K phosphorylation were observed in the NC line. Early knockdown of mTOR decreased proliferation, differentiation, and expression of myoblast determination protein 1 and myogenin in both lines independent of temperature, with the RBC2 line showing greater reductions in proliferation and differentiation than the NC line at 38° and 43°C. Proliferating SCs are more dependent on mTOR/S6K-mediated regulation than differentiating SCs. Thus, thermal stress can affect breast muscle hypertrophic potential by changing satellite cell proliferation and differentiation, in part, through the mTOR/S6K pathway in a growth-dependent manner. These changes may result in irreversible effects on the development and growth of the turkey p. major muscle.

Effect of Temperature and Selection for Growth on Intracellular Lipid Accumulation and Adipogenic Gene Expression in Turkey Pectoralis Major Muscle Satellite Cells

As multipotential stem cells, satellite cells (SCs) have the potential to express adipogenic genes resulting in lipid synthesis with thermal stress. The present study determined the effect of temperature on intracellular lipid synthesis and adipogenic gene expression in SCs isolated from the pectoralis major (p. major) muscle of 7-day-old fast-growing modern commercial (NC) turkeys compared to SCs from unselected slower-growing turkeys [Randombred Control Line 2 (RBC2)]. Since proliferating and differentiating SCs have different responses to thermal stress, three incubation strategies were used: (1) SCs proliferated at the control temperature of 38°C and differentiated at 43° or 33°C; (2) SCs proliferated at 43° or 33°C and differentiated at 38°C; or (3) SCs both proliferated and differentiated at 43°, 38°, or 33°C. During proliferation, lipid accumulation increased at 43°C and decreased at 33°C with the NC line showing greater variation than the RBC2 line. During proliferation at 43°C, peroxisome proliferator-activated receptor-γ (PPARγ) and neuropeptide-Y (NPY) expression was reduced to a greater extent in the NC line than the RBC2 line. At 33°C, expression of PPARγ, NPY, and CCAAT/enhancer-binding protein-β (C/EBPβ) was upregulated, but only in the RBC2 line. During differentiation, both lines showed greater changes in lipid accumulation and in C/EBPβ and NPY expression if the thermal challenge was initiated during proliferation. These data suggest that adipogenic gene expression is more responsive to thermal challenge in proliferating SCs than in differentiating SCs, and that growth-selection has increased temperature sensitivity of SCs, which may significantly affect breast muscle structure and composition.

Phosphorylation state of pyruvate dehydrogenase and metabolite levels in turkey skeletal muscle in normal and pale, soft, exudative meats

ABSTRACT 1. Turkey production has increased dramatically as genetic selection has succeeded in increasing body weight and muscle yield to fulfil increasing consumer demand. However, producing fast-growing, heavily muscled birds is linked to increased heat stress susceptibility and can result in pale, soft, exudative (PSE) meat. Previous studies indicated that pyruvate dehydrogenase kinase 4 (PDK4) is significantly reduced in PSE samples, suggesting this as a candidate gene associated with the development of this problem. 2. The objective of this study was to determine whether pre-market thermal challenge results in PSE meat as a result of differential expression of PDK4. Two genetic lines of turkeys were used in this study; the Randombred Control Line 2 (RBC2) and a commercial line. Turkeys were exposed to a pre-market thermal challenge of 12 h at 35°C followed by 12 h at 27°C for 5 d. Birds were slaughtered and processed according to industry standards. Pectoralis major samples were categorised as PSE or normal based on marinade uptake and cook loss indicators. In the first experiment, the relative expression of pyruvate dehydrogenase (PDH) and the phosphorylation state of PDH in normal and PSE turkey meat were analysed by western blotting. In the second experiment, the same samples were used to measure metabolite levels at 5 min post-mortem, comparing the normal to the PSE samples. 3. The results of the first experiment showed that PSE samples had significantly lower total PDH (P = 0.029) compared to normal meat. However, there was no significant difference in the degree of phosphorylation of sites 1, 2 or 3. In the second experiment, there were no significant differences in glycogen, lactate, glycolytic potential or ATP when comparing PSE to control samples. 4. These results suggested that a reduction in PDK4 expression alone does not explain the development of PSE meat.

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.

Research Note: Association of temporal expression of myostatin with hypertrophic muscle growth in different Japanese quail lines

Myostatin (MSTN) negatively regulates in muscle growth and development. Among alternative splicing isoforms of avian MSTN, MSTN-A has antimyogenic activities and MSTN-B functions as a promyogenic factor. In this study, different lines of Japanese quail were used: a random bred control (RBC) and a heavy weight (HW) quail line with muscle hypertrophy. The objectives of the current study are to compare temporal expression of the MSTN isoforms in pectoralis major muscle (PM) between 2 quail lines and to relate MSTN expression with temporal changes in muscle growth and total amounts of DNA in PM. Gains of body weight (BW) and PM weight were greater until posthatch day (D) 28 (P < 0.001), and the fold increases in total DNA contents of PM were greater in the HW line compared with the RBC line during D7 to D28 (P < 0.05). PCR analysis showed that MSTN-A expression was greater at 14 D (E14) of embryonic age (P < 0.01), D7 (P = 0.052), and D14 (P < 0.01) in the RBC line compared with the HW line. At D28 and D75, expression of MSTN-A was greater in the HW line compared with the RBC line (P < 0.05). MSTN-B expression was barely detectable from E14 to D14 and measurable from D28 to D75 in the muscle of both lines. Ratios of the MSTN-B/-A form ranging from 0.15 to 0.29 indicate a minor expression of the B form. Taken together, the lesser expression levels of MSTN-A at E14, D7, and D14 are associated with the fast growth of PM, and greater MSTN-A expression at D28 and D75 are associated with a slowdown of PM growth in the HW line. These data indicate a negative association of MSTN expression with PM growth and provide a scientific basis for potential usage of MSTN expression as a selection marker for greater muscle growth in poultry.

Research Note: Effect of selection for body weight on the adipogenic conversion of turkey myogenic satellite cells by Syndecan-4 and its covalently attached N-glycosylation chains

Adult myoblasts, satellite cells, will proliferate, and differentiate into myotubes in vitro. However, changes in environmental and nutritional conditions will result in the satellite cells differentiating into adipocyte-like cells synthesizing lipids. Prior research has shown that levels of N-glycosylation and heparan sulfate can promote or prevent the adipogenic conversion of myogenic satellite cells. Syndecan-4, an N-glycosylated heparan sulfate proteoglycan, has been shown to play key roles in satellite cell proliferation and migration. The objective of the current study was to determine if syndecan-4, and syndecan-4 N-glycosylation and heparan sulfate chain levels altered the conversion of satellite cells to an adipogenic cell fate and if growth selection affected the response of the satellite cells. Over-expression of syndecan-4, syndecan-4 without N-glycosylated chains but with its heparan sulfate chains attached, syndecan-4 without heparan sulfate chains with its N-glycosylation chains, and syndecan-4 without N-glycosylation and heparan sulfate chains was measured for lipid accumulation in pectoralis major muscle satellite cells isolated from the Randombred Control line 2 (RBC2) and 16 wk body weight (F line) turkeys. The F line was selected from the RBC2 line for only 16 wk body weight. Results from this study demonstrated that wild type levels of syndecan-4 and its covalently attached N-glycosylation chains play a key role in regulating the conversion of pectoralis major muscle satellite cells to an adipogenic lineage while selection for body weight was not a major contributing factor in this conversion.

Research Note: The effect of selection for 16-week body weight on turkey serum metabolome

The phenotype of modern commercial turkeys is substantially different than that of unselected, heritage turkey lines. These phenotypic changes have arisen from alterations in the genome/transcriptome, as well as the influence of many external factors on growth performance including nutrition, environment, and management. To investigate the phenotypic changes resulting from genetic selection for increased body weight, The Ohio State University maintains 2 unique genetic turkey lines: the randombred control (RBC2) line, which is comprised of genetics from 1960 era commercial turkeys and has been maintained without conscious selection for any trait; and the F line, which was originally selected from the RBC2 line and has been selected for increased 16 wk body weight for over 50 generations. This study used broad-spectrum mass-spectrometry profiling techniques to identify and quantify differences in the metabolome of the serum of F and RBC2 turkey lines. Serum samples from both F and RBC2 turkeys were subject to quantitative time of flight liquid chromatography tandem mass spectrometry analyses. Principle component analyses showed distinct populations of metabolites in the F vs. RBC2 serum, suggesting that increased body weight is associated with the accumulation of several metabolites. Comparing the spectral features to online databases resulted in the selection of 104 features with potentially identifiable chemical structures. Of these 104 features, 25 were found at higher levels in the serum of the RBC2 line turkeys, while 79 were found at a greater abundance in the F line turkeys. A more detailed analysis of these 104 features allowed for the putative identification of 49 compounds, which were clustered into 6 functional groups: 1) energy metabolism; 2) vitamins; 3) hormones and signaling molecules; 4) lipid derivatives, fatty acid metabolites, and membrane components; 5) amino acid/protein metabolism; and 6) microbial metabolites. Further validation and experimentation is needed to confirm the identity of these metabolites and understand their biological relevance and association with selection for increased body weight.

Effects of Divergently Selected Broiler Lines for Meat Color on Pseudomonas Growth Under Simulated Retail Display

ObjectivesSelection of broilers based on L* values have affected the meat pH of broiler breast meat. The objective is to determine if the selection of L* values have affected Pseudomonas ssp. growth under simulated retail display.Materials and MethodsBroilers from the 13th generation of three different lines (n = 30/line) selected for high L* (HMC), low L* (LMC) and a random bred control (RBC) were harvested at 7 wk of age. Carcasses were weighed and deboned after a 4 h postmortem (PM) chill. Parts were weighed to determine parts yield based on chilled carcass weight. Meat pH was determined 24 h PM and 24 h drip loss was determined. Split breasts were weighed, packaged, displayed under simulated retail conditions, and sampled on display Days 0, 1, 2, and 3 for instrumental color and microbial count of Pseudomonas ssp.ResultsChilled carcass weight was greater (P &lt; 0.05) in the HMC and RBC lines than the LMC line. Percent yield of breast, wing, leg and rack were not different (P &gt; 0.05) among the three lines. The LMC and RBC lines had greater (P &lt; 0.05) tenderloin yield compared to the HMC line. The LMC line had greater (P &lt; 0.05) meat pH followed by the RBC line and then the HMC line. The HMC line had greater (P &lt; 0.05) L*, b* and hue values followed by RBC line and then LMC line. The LMC line had greater (P &lt; 0.05) a* values and oxymyoglobin ratio followed by RBC line and then LMC line. There was no difference (P &gt; 0.05) in chroma among the three lines. After 24 h PM, the HMC line had more (P &lt; 0.05) percent drip loss than the LMC and RBC lines but there was no difference (P &gt; 0.05) in package drip loss from the start of simulated display to end of simulated display among the three lines. On each display day, the LMC line had increased counts of Pseudomonas ssp. compared to the RBC and LMC lines. Counts of Pseudomonas ssp. was similar between RBC and LMC lines on display Days 0, 2, and 3 with RBC line having increased counts on display Day 1 compared to the HMC line. There was a weak correlation (r = 0.12) between meat pH and counts of Pseudomonas ssp.ConclusionSelection for L* affected chilled carcass weights and percent yield of tenderloins, but not any other part yields. The growth of Pseudomonas ssp. is affected by the lines selected for L* but the relationship of meat pH and the growth of Pseudomonas ssp. is weak.

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.

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 72h 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 48h 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 24h 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.

Continual Selection for Increased 16 wk Body Weight on Turkey Growth and Meat Quality: 50 Generation Update

SUMMARY Today commercial turkeys have an average body weight of nearly 17 kg within 16 wk of age. Approximately 50 yr prior, commercial turkeys reached 5 to 7 kg in the same period of time. Much of the increased growth can be attributed to genetic advances attained through selection for greater body weight, feed efficiency, and meat yield. Recent meat quality challenges have arisen and are attributed to the rapid growth of commercial turkeys. In the current study, 2 lines of turkeys were compared: the Randombred Control Line 2 (RBC2), which is representative of a late 1960’s commercial turkey and has been maintained without conscious selection for any trait, and the F line which was selected for only increased 16 wk body weight from the RBC2 line. After 50 generations of selection for increased body weight, the F line turkeys are now 2.5-times heavier than the RBC2 turkeys. Even with the increased weight gain, feed conversion rate was not different between the F and RBC2 lines. The pectoralis major (p. major: breast muscle) from the F line turkeys contained significantly more intramuscular fat compared to breasts from the RBC2 turkeys. Fresh breast color and shear force were not significantly different between the 2 lines. The results from the current study demonstrate that 50 generations of selection for increased 16 wk body weight has minimally impacted fresh meat quality. However, increased intramuscular fat content may deter consumers whom select turkey products due to it being a high-quality low fat source of protein.

The effect of nutrient restriction on the proliferation and differentiation of turkey pectoralis major satellite cells differing in age and growth rate

Myogenic satellite cells are critical for posthatch muscle growth, and their activity is sensitive to nutritional regime during the immediate posthatch period. The objective of the current study was to determine if the response of satellite cells to nutrient restriction was dependent on bird age and/or growth rate. Satellite cells were isolated from the pectoralis major (p. major) muscle of 1-d, 7-wk, and 16-wk-old turkeys selected for increased body weight at 16 wk of age (F line) and the randombred control (RBC2) line from which the F line was selected. Nutrient restriction of 0, 5, 10, 20, and 40% of the standard cell culture medium was applied during proliferation with subsequent normal differentiation medium (RN) or during differentiation with preceding normal proliferation medium (NR). Satellite cell proliferation and differentiation decreased with nutrient restriction for all treatment regimens and ages, except for 1-d cell differentiation with the RN treatment, which increased with nutrient restriction. Interestingly, after 24h of a 5% nutrient restriction during the RN treatment, proliferation increased for 1-d and 7-wk cells. Additionally, after 24h of 5, 10, and 20% nutrient restriction during the NR treatment, differentiation increased for 1-d and 7-wk cells. The 16-wk cells did not exhibit this response to any treatment regimen. Growth rate had little effect on satellite cell response to nutrient restriction. In this study, satellite cells differentially responded to nutrient restriction depending on age, as well as duration and timing of the nutrient restriction. These data suggest that it is necessary to optimize diets throughout a bird's life to maximize satellite cell activity and p. major muscle growth.

Effects of Divergently Selected Broiler Lines for Meat Color on Pseudomonas Growth Under Simulated Retail Display

ObjectivesSelection of broilers based on L* values have affected the meat pH of broiler breast meat. The objective is to determine if the selection of L* values have affected Pseudomonas ssp. growth under simulated retail display.Materials and MethodsBroilers from the 13th generation of three different lines (n = 30/line) selected for high L* (HMC), low L* (LMC) and a random bred control (RBC) were harvested at 7 wk of age. Carcasses were weighed and deboned after a 4 h postmortem (PM) chill. Parts were weighed to determine parts yield based on chilled carcass weight. Meat pH was determined 24 h PM and 24 h drip loss was determined. Split breasts were weighed, packaged, displayed under simulated retail conditions, and sampled on display Days 0, 1, 2, and 3 for instrumental color and microbial count of Pseudomonas ssp.ResultsChilled carcass weight was greater (P < 0.05) in the HMC and RBC lines than the LMC line. Percent yield of breast, wing, leg and rack were not different (P > 0.05) among the three lines. The LMC and RBC lines had greater (P < 0.05) tenderloin yield compared to the HMC line. The LMC line had greater (P < 0.05) meat pH followed by the RBC line and then the HMC line. The HMC line had greater (P < 0.05) L*, b* and hue values followed by RBC line and then LMC line. The LMC line had greater (P < 0.05) a* values and oxymyoglobin ratio followed by RBC line and then LMC line. There was no difference (P > 0.05) in chroma among the three lines. After 24 h PM, the HMC line had more (P < 0.05) percent drip loss than the LMC and RBC lines but there was no difference (P > 0.05) in package drip loss from the start of simulated display to end of simulated display among the three lines. On each display day, the LMC line had increased counts of Pseudomonas ssp. compared to the RBC and LMC lines. Counts of Pseudomonas ssp. was similar between RBC and LMC lines on display Days 0, 2, and 3 with RBC line having increased counts on display Day 1 compared to the HMC line. There was a weak correlation (r = 0.12) between meat pH and counts of Pseudomonas ssp.ConclusionSelection for L* affected chilled carcass weights and percent yield of tenderloins, but not any other part yields. The growth of Pseudomonas ssp. is affected by the lines selected for L* but the relationship of meat pH and the growth of Pseudomonas ssp. is weak.

Response of Turkey Muscle Satellite Cells to Thermal Challenge. II. Transcriptome Effects in Differentiating Cells.

Background: Exposure of poultry to extreme temperatures during the critical period of post-hatch growth can seriously affect muscle development and thus compromise subsequent meat quality. This study was designed to characterize transcriptional changes induced in turkey muscle satellite cells by thermal challenge during differentiation. Our goal is to better define how thermal stress alters breast muscle ultrastructure and subsequent development.Results: Skeletal muscle satellite cells previously isolated from the Pectoralis major muscle of 7-wk-old male turkeys (Meleagris gallopavo) from two breeding lines: the F-line (16 wk body weight-selected) and RBC2 (randombred control line) were used in this study. Cultured cells were induced to differentiate at 38°C (control) or thermal challenge temperatures of 33 or 43°C. After 48 h of differentiation, cells were harvested and total RNA was isolated for RNAseq analysis. Analysis of 39.9 Gb of sequence found 89% mapped to the turkey genome (UMD5.0, annotation 101) with average expression of 18,917 genes per library. In the cultured satellite cells, slow/cardiac muscle isoforms are generally present in greater abundance than fast skeletal isoforms. Statistically significant differences in gene expression were observed among treatments and between turkey lines, with a greater number of genes affected in the F-line cells following cold treatment whereas more differentially expressed (DE) genes were observed in the RBC2 cells following heat treatment. Many of the most significant pathways involved signaling, consistent with ongoing cellular differentiation. Regulation of Ca2+ homeostasis appears to be significantly affected by temperature treatment, particularly cold treatment.Conclusions: Satellite cell differentiation is directly influenced by temperature at the level of gene transcription with greater effects attributed to selection for fast growth. At lower temperature, muscle-associated genes in the satellite cells were among the genes with the greatest down regulation consistent with slower differentiation and smaller myotubes. Fewer expression differences were observed in the differentiating cells than previously observed for proliferating cells. This suggests the impact of temperature on satellite cells occurs primarily at early points in satellite cell activation.

Genome re-sequencing to identify single nucleotide polymorphism markers for muscle color traits in broiler chickens.

ObjectiveMeat quality including muscle color in chickens is an important trait and continuous selective pressures for fast growth and high yield have negatively impacted this trait. This study was conducted to investigate genetic variations responsible for regulating muscle color.MethodsWhole genome re-sequencing analysis using Illumina HiSeq paired end read method was performed with pooled DNA samples isolated from two broiler chicken lines divergently selected for muscle color (high muscle color [HMC] and low muscle color [LMC]) along with their random bred control line (RAN). Sequencing read data was aligned to the chicken reference genome sequence for Red Jungle Fowl (Galgal4) using reference based genome alignment with NGen program of the Lasergene software package. The potential causal single nucleotide polymorphisms (SNPs) showing non-synonymous changes in coding DNA sequence regions were chosen in each line. Bioinformatic analyses to interpret functions of genes retaining SNPs were performed using the ingenuity pathways analysis (IPA).ResultsMillions of SNPs were identified and totally 2,884 SNPs (1,307 for HMC and 1,577 for LMC) showing >75% SNP rates could induce non-synonymous mutations in amino acid sequences. Of those, SNPs showing over 10 read depths yielded 15 more reliable SNPs including 1 for HMC and 14 for LMC. The IPA analyses suggested that meat color in chickens appeared to be associated with chromosomal DNA stability, the functions of ubiquitylation (UBC) and quality and quantity of various subtypes of collagens.ConclusionIn this study, various potential genetic markers showing amino acid changes were identified in differential meat color lines, that can be used for further animal selection strategy.

Influence of temperature and growth selection on turkey pectoralis major muscle satellite cell adipogenic gene expression and lipid accumulation

Immature poults have an inefficient thermoregulatory system, and therefore extreme ambient temperatures can impact their internal body temperature. Satellite cells, the only posthatch myonuclei source, are multipotential stem cells and sensitive to temperature. Selection for faster-growing, high-yielding birds has altered satellite-cell properties. The objective of the current study was to determine how temperature affects adipogenic properties of satellite cells isolated from the pectoralis major (p. major) muscle of Randombred Control line (RBC2) and F line turkeys selected only for increased 16-wk body weight from the RBC2 line. Satellite cells were cultured at 2°C incremental temperatures between 33 and 43°C and compared to cells cultured at the control temperature of 38°C to ascertain temperature effects on lipid accumulation and expression of adipogenic genes: CCAAT/enhancer-binding protein-β (C/EBPβ), peroxisome proliferator-activated receptor-γ (PPARγ), and stearoyl-CoA desaturase (SCD). During proliferation, the amount of quantifiable lipid in both F and RBC2 satellite cells increased at temperatures above 38°C (P < 0.01) and decreased at temperatures below 38°C (P < 0.01). Above 38°C, RBC2 satellite cells had more lipid (P = 0.02) compared to the F line, whereas there were few differences between lines below 38°C. At 72 h of proliferation, expression of C/EBPβ, PPARγ, and SCD decreased (P ≤ 0.02) as temperatures increased from 33 to 43°C in both cell lines. During differentiation expression of C/EBPβ increased (P < 0.01) as temperatures increased from 33 to 43°C in both cell lines. In F line satellite cells, PPARγ expression decreased (P < 0.01) with increasing temperatures during differentiation, whereas there was no linear trend in RBC2 cells. During differentiation expression of SCD increased as temperatures increased (P < 0.01) in RBC2 cells, and there was no linear trend within the F line. Results from the current study suggest that environmental temperature can affect p. major satellite cellular fate; however, selection for increased body weight had little impact on these cellular responses.