title: Prolonged fasting and cortisol reduce myostatin mRNA levels in tilapia larvae; short-term fasting elevates.
abstract: Myostatin negatively regulates muscle growth and development and has recently been characterized in several fishes. We measured fasting myostatin mRNA levels in adult tilapia skeletal muscle and in whole larvae. Although fasting reduced some growth indexes in adults, skeletal muscle myostatin mRNA levels were unaffected. By contrast, larval myostatin mRNA levels were sometimes elevated after a short-term fast and were consistently reduced with prolonged fasting. These effects were specific for myostatin, as mRNA levels of glyceraldehyde-3-phosphate dehydrogenase and glucose-6-phosphatase were unchanged. Cortisol levels were elevated in fasted larvae with reduced myostatin mRNA, whereas in addition immersion of larvae in 1 ppm (2.8 microM) cortisol reduced myostatin mRNA in a time-dependent fashion. These results suggest that larval myostatin mRNA levels may initially rise but ultimately fall during a prolonged fast. The reduction is likely mediated by fasting-induced hypercortisolemia, indicating divergent evolutionary mechanisms of glucocorticoid regulation of myostatin mRNA, since these steroids upregulate myostatin gene expression in mammals.
authors.affiliation: Department of Pediatrics, Division of Endocrinology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21208, USA. drodgers@jhmi.edu
authors.forename: Buel D
authors.initials: BD
authors.lastname: Rodgers
authors.forename: Gregory M
authors.initials: GM
authors.lastname: Weber
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Kelley
authors.forename: Michael A
authors.initials: MA
authors.lastname: Levine
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D003001:Cloning, Molecular; D005215:Fasting / Q000502:physiology*; D005508:Food Deprivation; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects*; D005952:Glucose-6-Phosphatase / Q000235:genetics; D024581:Glyceraldehyde-3-Phosphate Dehydrogenase (Phosphorylating) / Q000235:genetics; D006854:Hydrocortisone / Q000494:pharmacology*; D007814:Larva / Q000187:drug effects* / Q000235:genetics; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism; D055435:Myostatin; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012337:RNA, Ribosomal, 18S / Q000235:genetics; D017210:Tilapia / Q000235:genetics* / Q000254:growth & development*; D013997:Time Factors; D016212:Transforming Growth Factor beta / Q000235:genetics*
chemical_list: D055435:Myostatin; D012333:RNA, Messenger; D012337:RNA, Ribosomal, 18S; D016212:Transforming Growth Factor beta; D024581:Glyceraldehyde-3-Phosphate Dehydrogenase (Phosphorylating); D005952:Glucose-6-Phosphatase; D006854:Hydrocortisone