Molecular characterization, tissue distribution patterns and nutritional regulation of IGFBP-1, -2, -3 and -5 in yellowtail, Seriola quinqueradiata.

Insulin-like growth factor-binding proteins (IGFBPs) play a vital role in regulating the biological activities of IGFs. In this study, we cloned and determined full-length cDNA sequences of yellowtail IGFBP-1, -2, -3 and -5. Their tissue distribution was determined by real-time quantitative RT-PCR, which revealed that IGFBP-1, -2, -3 and -5 are widely distributed in yellowtail tissues. In yellowtail, both IGFBP-1 and -2 are highly expressed in the liver, IGFBP-3 is predominantly expressed in the heart and skin, with the lowest expression in the liver, and IGFBP-5 is highly expressed in the liver and kidneys. The widespread tissue expression of the yellowtail IGFBPs suggests that they may act in an autocrine and/or paracrine manner in the regulation of IGF activity. The effects of nutritional deprivation on yellowtail IGFBPs and IGF-I were also examined. During a 15-day starvation period, significant elevation was observed in hepatic yellowtail IGFBP-1. Refeeding restored its level to that of the control. No significant change was observed in the hepatic yellowtail IGFBP-2 mRNA levels in starved fish compared with control fish during the starvation period. Interestingly, during the early period of food deprivation, a significant increase was observed in hepatic yellowtail IGFBP-3 and -5 mRNA levels, concomitant to the significant elevation in hepatic IGF-I mRNA from day 3 to day 9. The unexpected increase in growth stimulatory IGFBPs and IGF-I during nutritional deprivation may represent a species-specific response to changes in nutritional condition.

Changes in mRNA expression of grouper (Epinephelus coioides) growth hormone and insulin-like growth factor I in response to nutritional status.

Growth hormone (GH) and insulin-like growth factor-I (IGF-I) are key links to nutritional condition and growth regulation in teleost. To understand the endocrine mechanism of growth regulation in grouper, we cloned the cDNAs for grouper GH and IGF-I and examined their mRNA expression during different nutritional status. Grouper GH cDNA is 936 base pairs (bp) long excluding the poly-A tail. It contained untranslated regions of 85 and 231bp in the 5'- and 3'-ends, respectively. It has an open reading frame of 612bp coding for a signal peptide of 17 amino acids (aa) and a mature hormone of 187aa residues. Based on the aa sequence of the mature hormone, grouper GH shows higher sequence identity (>76%) to GHs of perciforms than to GHs of cyprinids and salmonids (53-69%). Grouper preproIGF-I cDNA consisted of 558bp, which codes for 186aa. This is composed of 44aa for the signal peptide, 68aa for the mature peptide comprising B, C, A, and D domains, and 74aa for the E domain. Mature grouper IGF-I shows very high sequence identity to IGF-I of teleost fishes (84-97%) compared to advanced groups of vertebrates such as chicken, pig, and human (80%). Using DNA primers specific for grouper GH and IGF-I, the changes in mRNA levels of pituitary GH and hepatic IGF-I in response to starvation and refeeding were examined by a semi-quantitative RT-PCR. Significant elevation of GH mRNA level was observed after 2 weeks of food deprivation, and increased further after 3 and 4 weeks of starvation. GH mRNA level in fed-controls did not change significantly during the same period. Hepatic IGF-I mRNA level decreased significantly starting after 1 week of starvation until the 4th week. There was no significant change in IGF-I mRNA levels in fed-controls. One week of refeeding can restore the GH and IGF-I mRNA back to its normal levels. Deprivation of food for 1-4 weeks also resulted in cessation of growth and decrease in condition factor.