Expression patterns and immunolocalisation of IGF-I and IGF-II in male and female gonads of the Neotropical characid fish Astyanax fasciatus

The insulin-like growth factor (IGF) system plays important roles in fish reproduction, but the expression pattern and cellular location of IGF-I and IGF-II during gonadal maturation are uncertain. The present study reports a stage-specific assessment of gonadal expression levels and immunolocalisation of IGF-I and IGF-II in Astyanax fasciatus, a characid fish from South America. Adult fish in different maturity stages were caught in the Furnas Reservoir, Grande River, Brazil. Gonad samples were processed for histology, immunohistochemistry, and ELISA for IGF-I and IGF-II. Ovarian levels of IGF-I were low during ripening and ripe stages, higher in totally spent, and then decreased in resting. Levels of IGF-II increased during ovarian maturation, reaching significantly higher values at stage totally spent. In males, IGF-I levels followed gonadal maturation, with higher values in ripening and ripe stages, whereas IGF-II levels showed higher values in stage ripening and partially spent. A positive correlation was found between IGF-I and gonadosomatic index (GSI) for males (r = 0.59), while females showed a negative correlation (r = - 0.43), but IGF-II showed no correlation to GSI. IGF-I was expressed mainly in oogonia nests whereas IGF-II stained the follicular cells in the perinucleolar follicles, cortical vesicles in the previtellogenic follicles, and oogonia nests. In males, IGF-I was evident in spermatogonia and spermatocytes while IGF-II stained Sertoli cells surrounding spermatids cysts and spermatogonia in late stages. Together, these findings support a hypothesis that the balance between IGF-I and IGF-II levels is important in the regulation of gonad maturation in Astyanax fasciatus.