Immunohistochemical localization of vitellogenin in rainbow trout (Oncorhynchus mykiss) hepatocytes using immunofluorescence

In fish, vitellogenin, the egg yolk protein precursor of any oviparous spec ies, is specifically synthesized in the liver of females in response to cir culating estrogens. It is released into the blood, taken up by the ovary an d used to form the yolk in the eggs. In order to localize vitellogenin in h epatocytes of rainbow trout (Oncorhynchus mykiss) after external stimulatio n, both male and female fish were given a single intraperitoneal injection of 17 beta-estradiol at 1 mg/kg. Whereas in control male liver vitellogenin could not be demonstrated, both sexes produced vitellogenin after 17 beta- estradiol stimulation. Induced male fish displayed the same pattern of anti body binding as female individuals. However, in males the staining intensit y was lower than in females. Under the light microscope, antibodies primari ly bound to perinuclear regions, which contain, among other organelles, rou gh endoplasmic reticulum and Golgi fields, where vitellogenin is synthesize d. Under the electron microscope, these organelles could be confirmed as th e sites of vitellogenin synthesis by means of specific antibody labeling. ( C) 1999 Elsevier Science B.V. All rights reserved.