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Myogenic satellite cells are an adult stem cell responsible for all post-hatch muscle growth in poultry. As a stem cell population, satellite cells are highly heterogeneous, but the origin of this heterogeneity remains unclear. Heterogeneity is, in part, regulated by gene expression. One method of endogenous gene regulation that may contribute to heterogeneity is microRNAs (miRNAs). Two miRNAs previously shown to regulate poultry myogenic satellite cell proliferation and differentiation, miR-128 and miR-24, were studied to determine if they also affected satellite cell migration. Satellite cell migration is an essential step for both proliferation and differentiation. During proliferation, satellite cells will migrate and align to form new myofibers or donate their nuclei to existing myofibers leading to muscle fiber hypertrophy or regeneration. Transient transfection of miRNA specific mimics to each miRNA reduced migration of satellite cells following a cell culture scratch at 72 h of proliferation when the cultures were 90 to 100% confluent. However, only the migration in cells transfected with miR-24 mimics at 24 and 30 h following the scratch was significantly reduced (P ≤ 0.05) to around 70% of the distance migrated by controls. Alternately, transfection with inhibitors specific to miR-128 or miR-24 significantly (P ≤ 0.05) increased migration between 147 and 252% compared to their controls between 24 and 48 h following the scratch. These data demonstrate that miR- 128 and miR-24 play a role in myogenic satellite cell migration, which will impact muscle development and growth. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The wooden breast (WB) myopathy is identified by the palpation of a rigid pectoralis major (p. major) muscle and is characterized as a fibrotic, necrotic p. major disorder in broilers. The objective of the current study was to determine spatial morphological and gene expression differences at 4 locations within WB affected muscle from different genetic lines. Morphology was evaluated in 2 broiler lines expressing the WB myopathy (Lines A and B) and a line without WB (Line C) at 3 ventral locations and one anterodorsal location in the p. major muscle. In WB affected muscle of Line A, fibrosis was greatest in the anterior locations of WB affected muscle. In Line B muscle, fibrosis was greatest in the anteroventral region and minimal in the anterodorsal or posterior regions. Average p. major myofiber diameter was 30% larger in Lines A and B compared to Line C. However, in Line A there were no differences between the percentage of large fibers (diameter >70 μm) in unaffected and WB affected muscles at any sampling region. The percentage of small fibers (diameter <10 μm), likely small regenerating fibers, and expression of myogenic determination factor 1 (MYOD1) and myogenin were increased in Line A WB affected muscle compared to unaffected muscle. In Line B, the percentage of small fibers and MYOD1 expression in WB affected muscle was not different from unaffected muscle. Connective tissue organization within WB affected muscle was also different in Lines A and B, which may be attributed to decorin, a proteoglycan that mediates collagen crosslinking, growth factor signaling, and cell growth. Decorin expression was increased at all locations within Line A. However, in Line B decorin was increased only in the fibrotic regions of the p. major. The compiled results provide evidence that the WB myopathy is not uniform throughout the entire p. major muscle and the anterior end of the p. major muscle was more affected by the condition. [ABSTRACT FROM AUTHOR]

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 PPAR-γ 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. [ABSTRACT FROM AUTHOR]

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 fullfed (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. [ABSTRACT FROM AUTHOR]

Our previous transcriptional profiling study using a turkey skeletal muscle-specific oligonucle-otide microarray revealed over 3,000 genes that were differentially expressed at 3 critical stages of muscle development: 18 d embryonic, 1 d posthatch, and 16 wk of age. The genes versican, matrix Gla protein (MGP), and death-associated protein (DAP) were selected to study for their potential effects on muscle satellite cell proliferation and differentiation, as their functions in other tissues are suggestive of possible key roles in the regulation of myogenesis and they are differentially ex-pressed throughout muscle development in the turkey. Using small interfering RNA to knockdown the expression of these genes during proliferation and differentia-tion, each of the genes was found to differentially affect proliferation and differentiation. Versican and MGP predominantly affected proliferation with line effects, but later stages of differentiation were affected by the knockdown of versican and MGP. The underexpression of DAP inhibited myotube formation, which is a neces-sary stage in the development of muscle fibers. With-out myotube development, muscle fiber formation will be inhibited or abolished. This is the first report that these genes with no previously documented functions with regard to muscle development play a critical role in muscle cell proliferation and differentiation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Posthatch muscle growth is determined by the activation, differentiation, and fusion of satellite cells. Satellite cells composing an individual muscle are heterogeneous, which will differentially affect muscle growth. The proliferation and differentiation of turkey primary pectoralis major muscle cells were investigated in vitro at :1 d of age and at 4, 8, 16, 26, 35, 45, and 54 wk of age. The turkey was selected for these studies because turkey skeletal muscle fibroblasts do not grow in primary muscle cell cultures. Results from the proliferation analysis showed a decrease in proliferation by 8 wk of age. Differentiation into myotubes was significantly decreased by 4 wk of age and myotube diameter was decreased. The changes in muscle weight relative to total BW were measured for the anterior latissirnus dorsi, biceps brachii, pectoralis major, sartorius, biceps femoris, and gastrodnemius muscles to compare the relative growth of different muscles. The age at which the muscles reached their maximum relative weight was muscle-dependent, with the biceps brachii plateauing the earliest at 4 wk and the sartorius the latest at 45 wk of age. These data suggested that changes in inyogenic cells begin to occur early in muscle development and the activity of the satellite cells during these initial stages of posthatch growth is critical in overall muscle mass accumulation. [ABSTRACT FROM AUTHOR]

ABSTRACT Delta-like protein 1 (DLK1) has been implicated in the muscle hypertrophy observed in DLK1 transgenic mice, callipyge sheep, and mouse paternal uniparental disomy 12 and human paternal uniparental disomy 14 syndromes. The current study was aimed to determine chicken DLK1 (gDLK1) mRNA expression during primary muscle cell differentiation and during muscle regeneration after cold injury and to compare gDLK1 mRNA expression during skeletal muscle development in layers and broilers. In chicken primary muscle cell culture, gDLK1 rriRNA expression was significantly increased from 12 to 48 h (P < 0.05) when the nascent myotubes were actively formed at d 2 to 3. Myogenin, a late myogenic marker gene, mRNA expression peaked at 36 to 48 h. Myogenic differentiation 1 (MyoD) and paired box gene 7 (Pax7), early myogenic marker genes, mRNA expression gradually decreased during myogenic differentiation. During muscle degeneration, the expression of MyoD and Pax7 peaked at d 2 (P < 0.05), and myogenin rnRNA expression peaked at d 4 (P ⩽ 0.05). The induction of gDLK1 gene appeared between d 7 to 10 postinjury (P < 0.05) when myotubes were actively formed as also demonstrated in histological sections. The expression of gDLK1 was slowly downregulated to the control levels at d 14 when the damaged muscle appeared nearly healed. These data suggest that gDLKII may be involved in the late myogenic stages of piimary muscle cell differentiation and muscle regeneration. The gDLK1 mRNA in the muscle tissues was very abundant at embryonic ages but decreased after hatching in both broiler and layer chickens. Compared with layers, broiler muscle at embryonic d 13 had a 3-fold greater expression of DLK1 (P ⩽ 0.01). In addition, the gDLK1 mRNA expression at d 1, 1:1, and 33 posthatch was significantly higher in broilers than layers (P 0.05). Therefore, the relatively greater expression of the gDLK1 gene in muscles of broilers compared with layers suggests that gDLK1 may serve as a new selection marker for high nmscle growth in chickens. These findings may provide new insight into chicken muscle development and regeneration. [ABSTRACT FROM AUTHOR]

During skeletal muscle development, transforming growth factor-β1 (TGF-β1) is a potent inhibitor of muscle cell proliferation and differentiation, as well as a regulator of extracellular matrix (ECM) production. Decorin, a member of the small leucine-rich ECM proteoglycans, binds to TGF-β1 and modulates TGF-β1-dependent cell growth stimulation or inhibition. The expression of decorin can be regulated by TGF-β1 during muscle proliferation and differentiation. How TGF-β1 affects decorin and muscle growth, however, has not been well documented in vivo. The present study investigated the effect of TGF-β1 on decorin expression and intracellular connective tissue development during skeletal muscle growth. Exogenous TGF-β1 significantly decreased the number of myofibers in a given area at both 1 d and 6 wk posthatch. The TGF-β1-treated muscle had a significant decrease in decorin mRNA expression at embryonic day (ED) 10, whereas protein amounts decreased at 17 ED and 1 d posthatch compared to the control muscle. Decorin was localized in both the endomysium and perimysium in the control pectoralis major muscle. Transforming growth factor-β1 reduced decorin in both the endomysium and perimysium from 17 ED to 6 wk posthatch. Compared to the control muscle, the perimysium space in the pectoralis major muscle was dramatically decreased by TGF-β1 during embryonic development through posthatch growth. Because decorin regulates collagen fibrillogenesis, a major component of the ECM, the reduction of decorin by TGF-β1 treatment may cause the irregular formation of collagen fibrils, leading to the decrease in endomysiurn and perimysium space. The results from the current study suggest that the effect of TGF-β1 on decorin expression and localization was likely associated with altered development of the perimysium and the regulation of muscle fiber development. [ABSTRACT FROM AUTHOR]

During skeletal muscle development, transforming growth factor-β1 (TGF-β1) is a potent inhibitor of muscle cell proliferation and differentiation. The TGF-β1 signal is carried by Smad proteins into the cell nucleus, inhibiting the expression of key myogenic regulatory factors including MyoD and myogenin. However, the molecular mechanism by which TGF-β1 inhibits muscle cell proliferation and differentiation has not been well documented in vivo. The present study investigated the effect of TGF-β1 on in vivo skeletal muscle growth and development. A chicken line, Low Score Normal (LSN) with reduced muscling and upregulated TGF-β1 expression, was used and compared to a normal chicken line. The injection of TGF-β1 at embryonic day (ED) 3 significantly reduced the pectoralis major (p. major) muscle weight in the normal birds at 1 wk posthatch, whereas no significant difference was observed in the LSN birds. The difference between normal and LSN birds in response to TGF-β1 is likely due to different levels of endogenous TGF-β1 where the LSN birds have increased TGF-β1 expression in their p. major muscle at both 17 ED and 6 wk posthatch. Smad3 expression was reduced by TGFβ1 from 10 ED to 1 wk posthatch in normal p. major muscle. Unlike Smad3, Smad7 expression was not significantly affected by TGF-β1 until posthatch in both normal and LSN p. major muscle. Expression of MyoD was reduced 35% by TGF-β1 during embryonic development in normal p. major muscle, whereas LSN p. major muscle showed a delayed decrease at 1 d posthatch in MyoD expression in response to the TGF-β1 treatment. Myogenin expression was reduced 29% by TGF-β1 after hatch in normal p. major muscle. In LSN p. major muscle, TGF-β1 treatment significantly decreased myogenin expression by 43% at 1 d posthatch and 32% at 1 wk posthatch. These data suggested that TGF-β1 reduced p. major muscle growth by inhibiting MyoD and myogenin expression during both embryonic and posthatch development. Furthermore, TGF-β1 also reduced the expression of the cell adhesion receptor β1 integrin sub-unit during embryonic and posthatch muscle growth in normal and LSN chickens. Therefore, the reduction of β1 integrin in response to TGF-β1 is also associated with decreased posthatch muscle growth. The results from this study indicate that TGF-β1 inhibits skeletal muscle growth by regulating MyoD and myogenin expression. These data also suggest that a β1 integrin-mediated alternative pathway is likely involved in the TGF-β1-induced reduction of muscle growth. [ABSTRACT FROM AUTHOR]

The membrane-associated heparan sulfate proteoglycan families, consisting of the syndecans and glypicans, are low-affinity receptors for fibroblast growth factor 2 (FGF2) that are essential in regulating the cellular response to FGF2. Fibroblast growth factor 2 is a potent stimulator of skeletal muscle cell proliferation and a strong inhibitor of differentiation. The regulation of the expression of the syndecans and glypicans will likely play a role in modulating the effects of FGF2 on cellular growth properties. In the present study, the effect of FGF2 on the expression of syndecan-4 and glypican-1 was measured by real-time PCR during turkey myogenic satellite cell proliferation and differentiation in vitro. Both syndecan-4 and glypican-1 transcription were influenced by the addition of exogenous FGF2. Syndecan-4 mRNA expression was reduced only during proliferation, whereas glypican-i expression was reduced during both proliferation and differentiation. These results suggest that FGF2 growth factor signaling is, in part, regulated by an autoregulatory loop involving FGF2 regulation of syndecan-4 and glypican-1 expression and will affect the growth of skeletal muscle by modulating the proliferation and differentiation of satellite cells. [ABSTRACT FROM AUTHOR]

Pectoralis major muscle morphology was studied in both sexes of a turkey line (E) selected long-term for increased egg production and its randombred control (RBC1) from 25 d of incubation through 20 wk posthatch. Pectoralis major muscle samples from 10 individuals from each line-sex-age subgroup were obtained in a manner to prevent contraction. The muscle samples were dehydrated, cleared, embedded in paraffin, sectioned, incubated, and rehydrated before staining with hematoxylin and eosin. Representative sections were given a score by 4 individuals based on breast muscle morphology. The scores ranged from 1 (little extracellular matrix and indistinct muscle fibers) to 5 (large extracellular space and distinct muscle fibers). Scores from 2 to 4 were intermediate to these extremes. The pectoralis major muscle morphology scores were highest at 25 d of incubation and declined greatly at 1 wk of age. The scores increased from 1 to 4 wk of age and remained constant through 20 wk of age. Males had higher scores than females. In the current study, there was no significant difference between the E and RBC1 lines. Based on the results of 3 experiments (2 published and the present one) using the E and RBC1 lines, it appears that genetic increases in egg production may be associated with a slight reduction in pectoralis major muscle morphology scores at 16 wk of age. [ABSTRACT FROM AUTHOR]

The membrane-associated heparan sulfate proteoglycan families consisting of the syndecans and glypicans are low-affinity receptors for fibroblast growth factor 2 (FGF2). Fibroblast growth factor 2 is a potent stimulator of skeletal muscle cell proliferation and a strong inhibitor of differentiation. Because syndecan-1, syndecan-4, and glypican-1 potentially play unique, but pivotal, roles in muscle cell proliferation and differentiation, these proteoglycans were examined for their effect on muscle cell proliferation and differentiation and FGF2 responsiveness. In the present study, turkey Randombred Control 2 line myogenic satellite cells were transfected with expression vector constructions of syndecan-1, syndecan-4, or glypican-1 to assay their role during muscle development and the effect on FGF2 responsiveness. During proliferation, only syndecan-1 increased proliferation. Both syndecan-4 and glypican-1 decreased proliferation at 72 h but generally did not affect the proliferation process. There was no interaction between the transfected gene and cell proliferation response to FGF2. Glypican-1 increased differentiation early in the process (24 h), and at later times differentiation was decreased by glypican-1. Both syndecan-1 and syndecan-4 overexpression decreased differentiation. During differentiation, except for glypican-1 at 48 h of differentiation, there was no interaction between gene treatment and FGF2 responsiveness. This result indicates that FGF2 responsiveness was not affected by the overexpression of syndecan-1, syndecan- 4, and glypican-1 during differentiation. These data demonstrate that syndecan-1, syndecan-4, or glypican-1 differentially affect the processes of turkey muscle cell proliferation and differentiation, and can regulate these developmental stages in an FGF2-independent manner. [ABSTRACT FROM AUTHOR]

Muscle cell proliferation, migration, adhesion, and fusion are processes involved with the formation of multinucleated myotubes that will further differentiate into mature muscle fibers. The process of muscle fiber development is nearly complete at the time of hatch. Muscle growth during the embryonic period of development is characterized by an increase in myoblast cell number through hyperplasia. Posthatch muscle fiber growth occurs through muscle fiber enlargement by the process of hypertrophy, which results from the recruitment of satellite cell nuclei. Hyperplasia and hypertrophy are regulated by factors extrinsic to the cell. These extrinsic elements include growth factors and the extracellular matrix. The growth factors, hepatocyte growth factor, fibroblast growth factor 2, transforming growth factor-β, insulin-like growth factor, and myostatin stimulate or inhibit myoblast and satellite cell proliferation and differentiation. Some of these growth factors like fibroblast growth factor 2 must interact with a low affinity extracellular matrix macromolecule to bind to their high affinity receptor necessary for cell signaling. It is probable that the expression of extracellular matrix proteins involved in growth factor signaling will affect muscle growth properties during hyperplasia and hypertrophy. As signaling pathways associated with muscle growth mechanisms are further understood, the poultry industry may find it beneficial to include the expression of key genes in their selection strategies. [ABSTRACT FROM AUTHOR]

Breast muscle morphology was studied at 16 wk of age in a line (E) selected over 45 generations for increased egg production, its randombred control line (RBC1), and reciprocal crosses between the E and RBC1 lines. A sample of 10 birds per genetic group-sex sub- group was killed with restraint to prevent flapping of the wings. The skin was removed from the breast region and a sample of breast muscle was obtained in a manner to prevent contraction. The muscle samples were dehydrated, cleared, embedded in paraffin, sectioned, incubated, and rehydrated before staining with hematoxylin and eosin. Four sections from the same muscle from each bird were placed on a slide and the slides were viewed for muscle morphology characteristics with a microscope and digitally recorded. Five fields of each section were viewed. Representative sections of each bird were given a score by 4 individuals based on breast muscle morphology. The scores ranged from 1 (little extracellular matrix and indistinct muscle fibers) to 5 (large extracellular space and distinct muscle fibers). Scores from 2 to 4 were intermediate to these extremes. The data were analyzed for sexes separate and combined. The F line had lower breast muscle morphology scores than the RBC1 line for males and sexes combined, indicating additive genetic variation in the scores. Nonadditive genetic variation was not an important source of variation for breast muscle morphology scores based on the contrast of the average of the parental lines with the average of the reciprocal crosses for males, females, or sexes combined. In 5 of 6 possible comparisons, the breast muscle morphology scores of the reciprocal cross were not significantly different from the line of the dam in the reciprocal cross. The only exception was for the E sire × RBC1 dam cross based on the data for females, wherein the breast muscle morphology scores were higher in the cross than in the pure RBC1 line. The results of the current study confirm the maternal inheritance of breast muscle morphology scores at 16 wk of age that has been previously reported. [ABSTRACT FROM AUTHOR]

The heparan sulfate proteoglycans, syndecan-1 and glypican-1 (glypican), are low affinity receptors for fibroblast growth factor 2 (FGF2). Because FGF2 stimulates skeletal muscle cell proliferation but inhibits differentiation, changes in FGF2 signaling due to early posthatch feed deprivation may play a significant role in modulating muscle growth. To study the effect of early posthatch feed deprivation in chickens on heparan sulfate proteoglycan relative protein concentration, syndecan-1 expression, and glypican mRNA expression, pectoralis major muscle tissue was isolated from pretreatment d 0 chicis and chicks fed or feed deprived for 3 d, and after d 3 feeding was resumed in the feed-deprived birds until d 7. Heparan sulfate proteoglycan protein concentration was measured by ELISA analysis and was significantly decreased in the feed-deprived birds beginning at d 2 (P <0.05). The expression of syndecan-1 and glypican was measured by semi-quantitative reverse transcription PCR. Syndecan-1 expression was unaffected by feed withdrawal and refeeding (P > 0.05). Glypican mRNA expression was decreased in the muscle tissue from feed-deprived birds at d 3 (P < 0.05), but by d 7, after initiating feeding on d 4, it was significantly elevated compared with in muscle tissue from chicks maintained on feed (P <0.05). The results from the present study demonstrate that the heparan sulfate proteoglycan protein concentration and syndecan-1 and glypican mRNA expressions are differentially affected by early posthatch feed deprivation, which may alter signaling events associated with muscle growth. [ABSTRACT FROM AUTHOR]

Breast muscle morphology was studied at 8 and 16 wk of age in a line (E) selected over 44 generations for increased egg production and its randombred control line (RBC1). A sample of 20 birds per sex-line-age subgroup was killed with restraint to prevent flapping of the wings. The skin was removed from the breast region, and a sample of breast muscle was obtained in a manner to prevent contraction. The muscle samples were dehydrated, cleared, embedded in paraffin, sectioned, and incubated and rehydrated prior to staining with hematoxylin and eosin. Four sections from the same muscle from each bird were placed on a slide, and the slides were viewed for muscle morphological characteristics with a microscope and digitally recorded. Five fields of each section were viewed. Representative sections for each bird were given a score by 4 individuals based on breast muscle morphology. The scores ranged from 1 (little extracellular matrix and indistinct muscle fibers) to 5 (large extracellular space and distinct muscle fibers). Scores from 2 to 4 were intermediate to these extremes. Breast muscle morphology scores did not differ between lines or ages but there was a significant interaction between lines and ages. The scores increased in the RBC1 line from 8 to 16 wk of age, but the reverse was true for the E line. Scores were higher in males than females. The results of the present study suggest that selection for increased egg production in dam lines should not greatly influence breast muscle morphology in commercial turkeys. [ABSTRACT FROM AUTHOR]