LOCALIZATION OF INSULIN-LIKE GROWTH-FACTOR-I IMMUNOREACTIVITY IN LARVAL AND JUVENILE BARRAMUNDI (LATES-CALCARIFER)

Antisera to mammalian IGFs cross-react with several fish species, sugg esting a long phylogenetic history of IGF-like peptides and their func tional importance to all vertebrates. In this study, the tissue distri bution of IGF-I-immunoreactivity (IGF-I-IR) was studied at various lar val and juvenile stages of the life cycle of barramundi (Lares calcari fer). It was shown that the distribution of IGF-I-IR in this species w as tissue-specific and age-dependent. in newly hatched larvae, presump tive musculature in the trunk and the pectoral fin rudiments reacted p ositively for IGF-I. As specimen age increased, however, IGF-I-IR in t hese tissues became less evident. In the retinas of barramundi 42 hr a nd older, a distinct band of IGF-I-IR was consistently detected betwee n the presumptive outer nuclear and bacillary layers. Examination of s ections from specimens 9 days and older revealed strong reactivity for IGF-I in a large proportion of renal tubule epithelial cells. In sect ions from larvae 13 to 28 days old, diffuse cytoplasmic IGF-I-IR was i dentified in cells lining the gill structures, At these same developme ntal stages, IGF-I reactive cells were also observed in the islets of Langerhans. In young juveniles (22 to 28 days posthatching), sparsely scattered clusters of neurone in the lower brain were observed which e xhibited granular IGF-I-IR in perikarya. In all instances reported, IG F-I-IR in barramundi tissue was abolished by replacing antisera with n ormal rabbit serum or by preabsorption of antisera with purified IGF-I peptide, indicating the specificity of the reactions obtained. The di stribution patterns of IGF-I-IR in barramundi tissues were broadly con sistent with the reported distributions of IGF-I-like peptides and tra nscripts in other teleost species. The findings of this study are in g eneral agreement with the hypothesis that IGF-I-like peptides map be i nvolved in the regulation of tissue growth, differentiation, and funct ion during early barramundi development. (C) 1995 Academic Press, Inc.