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

In fish, vitellogenin, the egg yolk protein precursor of any oviparous species, is specifically synthesized in the liver of females in response to circulating estrogens. It is released into the blood, taken up by the ovary and used to form the yolk in the eggs. In order to localize vitellogenin in hepatocytes of rainbow trout Oncorhynchus mykiss. after external stimulation, both male and female fish were given a single intraperitoneal injection of 17b-estradiol at 1 mgrkg. Whereas in control male liver vitellogenin could not be demonstrated, both sexes produced vitellogenin after 17b-estradiol stimulation. Induced male fish displayed the same pattern of antibody binding as female individuals. However, in males the staining intensity was lower than in females. Under the light microscope, antibodies primarily bound to perinuclear regions, which contain, among other organelles, rough endoplasmic reticulum and Golgi fields, where vitellogenin is synthesized. Under the electron microscope, these organelles could be confirmed as the sites of vitellogenin synthesis by means of specific antibody labeling.