Submitted on October 18, 2002
Accepted on December 18, 2002
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 Pediatric Endocrinology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
2 USDA/ARS National Center for Cool and Cold Water Aquaculture, Kearneysville, WV, USA
3 Biological Sciences, California State University, Long Beach, CA, USA
* To whom correspondence should be addressed. E-mail: brodger1{at}jhmi.edu.
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 indices 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 while 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.
