NUTRITIONAL AND DEVELOPMENTAL REGULATION OF INSULIN-LIKE GROWTH-FACTORS IN FISH

The insulin-like growth factors (IGF) are evolutionarily ancient growt h factors present in all vertebrates. The central importance of IGF fo r normal development and growth has been illustrated by the severe gro wth-retarded phenotype exhibited by IGF-I, IGF-II or IGF-I receptor '' knockout'' mice. Although we know much about the gross effects of IGF on the overall size of the fetus and the clinical manifestations that result from fetal and neonatal deficiency of IGF (i.e., severe growth retardation leads to dwarfism), very little is known about the in vivo actions of IGF during embryogenesis at the cellular and molecular lev els. Most research on the developmental role of IGF has relied on rode nt models, and attempts to elucidate the molecular and cellular basis os' IGF actions have been hampered by the inaccessibility of the mamma lian fetus enclosed in the uterus. During the past decade, there has b een growing support for the concept that the IGF have been highly cons erved in all vertebrates. Both IGF-I and IGF-II are present in fish, a nd their structures are highly conserved. Human and fish IGF-I are equ ally potent in mammalian and fish bioassay systems. insulin-like growt h factor mRNA is found in all life stages of fish, ranging from unfert ilized egg to adult, The temporal and spatial expression patterns of f ish IGF-I seem to be similar to those in mammals. Nutritional status a nd growth hormone both have a profound effect on IGF-I expression in f ish, as they do in mammals. These features suggest that the IGF system is highly conserved between teleost: fish and mammals. Because fish e mbryos develop externally, they provide excellent animal models for un derstanding the regulatory roles of IGF, IGF receptor and IGF-binding proteins in vertebrate embryonic development, Current research on the developmental and nutritional roles of IGF in fish will undoubtedly co ntribute to knowledge of the basic physiology of vertebrates in genera l.