ROUTE OF EGG-YOLK PROTEIN-UPTAKE IN THE OOCYTES OF KURUMA PRAWN, PENAEUS-JAPONICUS

The route of egg yolk protein uptake into the oocytes of kuruma prawn, Penaeus japonicus, was studied using immunohistochemical and electron microscopical methods. Although a significant immunofluorescence with anti-vitellin-immunoglobulin was observed in the enlarged follicle ce lls surrounding oil globule stage oocytes of the early vitellogenic ov ary, no fluorescence was detected in shrunken follicle cells surroundi ng oocytes in the yolk granule stage. Electron microscopically, yolk g ranule stage oocytes have an irregular surface with numerous well-deve loped microvilli. In contrast, the surface of follicle cells is relati vely smooth. The irregular surface of yolk granule stage oocytes was c overed with a layer of electron dense material. Similar dense material was found in the spaces between the neighboring follicle cells on the yolk granule stage oocytes. The outer surface of the follicle cells o n yolk granule stage oocytes was covered by dense materials which were similar to those found on the irregular surface of oocytes. Micropino cytotic vesicles containing dense material were found in the ooplasm n ear the irregular surface with numerous well-developed microvilli. Den se material was concentrated in the peripheral part of the small formi ng yolk bodies of yolk granule stage oocytes. This suggests that the e lectron dense material, probably egg yolk protein, transferred to the surface of yolk granule stage oocytes from the spaces between the neig hboring follicle cells may be incorporated into the ooplasm by pinocyt osis through the microvilli and subsequently aggregate to form yolk bo dies.