Cloning and expression analysis of insulin-like growth factor I and II in liver and muscle of sea bass (Dicentrarchus labrax, L) during long-term fasting and refeeding.

The exceptionally fast growth that fish experience after periods of fasting has been called 'compensatory growth' or 'catch-up' growth. This phenomenon, reported in a wide range of fish species, has been studied in intensive aquaculture as a means of enhancing feed conversion efficiency, but the mechanisms implicated are complex and not yet fully understood. In the present study, the authors describe the cloning and sequencing of the complete coding sequences of sea bass (Dicentrarchus labrax) insulin-like growth factor-I (IGF-I) and insulin-like growth factor-II (IGF-II), which are potent mitogens known to play important roles in growth and development. Sea bass IGF-I has an open reading frame (ORF) of 561 bp that encodes a mature protein of 187 amino acids, whereas IGF-II has an ORF of 648 bp encoding a mature protein of 216 amino acids. At the amino acid level, sea bass IGF-I shares a 30% similarity with IGF-II. The authors then report the pattern of IGF-I and IGF-II gene expression in liver and myotomal muscle in response to prolonged fasting and refeeding. Nutritional status significantly influenced IGF-I messenger RNA copy number in both liver and muscle, inducing a down-regulation during fasting and an up-regulation during the recovery from fasting. The trend of IGF-II response was similar, but different feeding regimens did not affect the amounts of transcript as sharply as in IGF-I. Taken together these data indicate that IGF-I and IGF-II participate in promoting sea bass muscle compensatory growth induced by refeeding.