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Interaction between positive and negative effectors of embryonic and postnatal muscle growth in the chicken and the mouse [electronic resource] /

by Gahr, Scott Allen.

Abstract (Summary)
Interaction between positive and negative effectors of embryonic and postnatal muscle growth in the chicken and the mouse. Scott Allen Gahr Myostatin, belonging to the TGF-? family, negatively regulates skeletal muscle growth. The current study was conducted to assess the efficacy of in ovo administration of exogenous myostatin antagonist (MA) to enhance skeletal muscle growth and improve feed efficiency of broilers. Eggs were divided into three groups: uninjected control, vehicle-injected control and MA injected (600 ng per embryo). Eggs were injected once on either day 15 or 18 of embryogensis. In ovo administration of MA on day 15 resulted in the greatest increase in live weights (~8%, P < 0.10), breast weights (~14%, P < 0.05), leg weights (~10%, P < 0.10) and shank length (~7%, P < 0.01) in six-week old female broilers. Feed efficiency of the day 15 and day 18 MA injected mixed-sex broilers was unaffected at six weeks of age. Texture analysis showed the MA to have no effect on the shear force of the pectoralis muscle. Day 15 injected males did not have as pronounced effect as females in the measured variables. These findings suggest that in ovo administration of MA may provide a means to improve broiler productivity and profitability. Growth hormone secretion is under the control of a pair of hypothalamic factors, growth hormone releasing hormone and somatostatin. The growth hormone secretagogue receptor (GHSR) and its endogenous ligand represent a novel third mechanism regulating the release of growth hormone. Early chicken embryonic development, prior to day 14, has been proposed to be independent of GH. However, recent evidence shows that peripheral GH secretion has paracrine/autocrine functions during embryonic development. In the current study, we used the reverse-transcriptase polymerase chain reaction to determine the expression pattern of the GHSR during embryonic development and the effects of in ovo recombinant human (rh) IGF-I administration on its expression pattern. Eggs were injected once with 100 ng rhIGF-I in 10 mM acetic acid, and 0.1 % BSA per embryo on embryonic day 3. Total RNA was isolated from whole embryos on embryonic day E0-6 (n=6 per day), thoracic/abdominal halves of the embryos on E7-E8 (n= 6 per day) and Pectoralis muscle on E9-E20 (n= 4 per day). We found that GHSR expression was low during E0-E4, followed by an increase on E5 and remained constant through E17. GHSR expression then increased on E18 before reducing on E20. A similar pattern was found in the rhIGF-I treated embryos with the exception of a significant increase in GHSR expression on E8. These data indicate that the GHSR may be active in regulating GH secretion during early embryonic development, and upregulation of the GHSR gene following IGF-I administration may have an important role in the determination of postnatal muscle growth. Administration of the recently identified ligand of the growth hormone secretagoue receptor (GHSR) has been found to increase feed intake and fat deposition. During growth and aging, the myostatin knockout mouse has been shown to have a significant reduction in fat accumulation. In this study, we used RT-PCR to investigate the relationship between ghrelin and myostatin expression. Total RNA was isolated from the brain, heart, pectoralis muscle, kidney and liver of nine-month-old myostatin knockout (n=3) and control (n=3) mice. Ghrelin expression was significantly reduced in the heart (P < 0.05) and showed a trend for reduced expression in the pectoralis muscle (P=0.07) in myostatin knockout mice. However, ghrelin expression was not different in the brain, heart and liver between the control and myostatin knockout mice. These data indicate loss of myostatin may act by down regulating the expression of ghrelin to reduce the accumulation of fat in the myostatin knockout mouse. Additionally, these data are consistent with an autocrine/paracrine role for ghrelin, in the peripheral tissues, in metabolic regulation and nutrient partitioning.
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School:West Virginia University

School Location:USA - West Virginia

Source Type:Master's Thesis

Keywords:growth hormone releasing factor muscles chickens mice

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