Vol. 284, Issue 5, R1277-R1286, May 2003
Prolonged fasting and cortisol reduce myostatin mRNA levels
in tilapia larvae; short-term fasting elevates
Buel D.
Rodgers1,
Gregory M.
Weber2,
Kevin M.
Kelley3, and
Michael A.
Levine1
1 Department of Pediatrics, Division of
Endocrinology, Johns Hopkins University School of
Medicine, Baltimore, Maryland 21208; 2 US Department
of Agriculture/Agricultural Resource Service, National Center for
Cool and Cold Water Aquaculture, Kearneysville, West Virginia 25430;
and 3 Department of Biological Sciences, California
State University at Long Beach, Long Beach, California 90840
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 µM) 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.
muscle growth and development; Oreochromis mossambicus; growth/differentiating factor-8
