AMPHIBIAN BUFO-ARENARUM VITRONECTIN-LIKE PROTEIN - ITS LOCALIZATION DURING OOGENESIS

In the present study, we analyzed the localization of vitronectin-like protein in oocytes during oogenesis as well as in the serum and liver tissue of the amphibian Bufo arenarum. Vitronectin-like protein was p urified from serum by heparin-affinity chromatography and showed to ha ve the two biological properties in common with most animal vitronecti ns (VN): heparin binding activity and an RGD-dependent cell-spreading activity. SDS-PAGE of vitronectin-like protein revealed that it consis ts of two bands of 64 kDa and 72 kDa, while immunoblotting analyses sh owed that this protein strongly cross-reacts with two monoclonal antib odies against human VN. No immunofluorescent staining of vitronectin-l ike protein was observed in previtellogenic oocytes (stages I and II). In vitellogenic oocytes (stages Ill, IV and V) fluorescence was obser ved in the conical cytoplasm localized in yolk platelets, extending co ncomitantly with the vitellogenic process. When we examined the yolk p latelet formation pathway by immunoelectron microscopy, gold particles indicated that vitronectin-like protein was located on the yolk plate let precursors: multivesicular bodies and primordial yolk platelets. G old particles also were seen sparsely distributed in all oocyte invest ing layers. The mean serum vitronectin-like protein concentration in a mphibian animals was 127.8+/-11.6 mu g/ml in adult males and 181.5+/-1 4.3 mu g/ml in adult females. Serum vitronectin-like protein of males and females was susceptible to hormonal stimulation (17-beta estradiol ). These results suggest that vitronectin-like protein is stored in th e yolk platelets and may be involved in the later events of amphibian development.