The study of impacts of IGF-I, IGF-II, leucine and lysine starvation on myogenesis in gilthead sea bream cultured myocytes (Sparus aurata)

The insulin-like growth factors (IGFs) have a fundamental role in induction and improvement of growth in animals. Lysine and Leucine are limiting essential AA in fish, and it has been demonstrated that supplementation with them improves growth in different species. However, the specific effects of AA deficiencies in myogenesis are completely unknown. IGFs in muscle can affect the expression of components of the local IGF system. Thus, the response of all these genes to IGFs administration at two different times 6 and 18 hours in day 4 cultured myocytes of the same species was analyzed. Also, in this study, two isoforms of IGF-IRs were characterized in gilthead sea bream. Both IGFs increased the expression of IGF-I and IGFBP-5, but showed different effects on the receptors, with IGF-I suppressing the expression of both isoforms and IGF-II up-regulating IGF-IRb. Likewise, this study aimed to provide new information on the impact of Lysine and Leucine deficiencies in gilthead sea bream cultured myocytes in days 2, 4 and 8. Leucine deficiency did not cause significant differences in most of the molecules analyzed, whereas Lysine deficiency appeared crucial in IGFs regulation, decreasing significantly IGF-I, IGF-II and IGF-IRb mRNA levels. It demonstrates the importance of an adequate level of Lysine in fishmeal diet formulation for optimum growth.