Receptor‐mediated transport of vitellogenin during oogenesis of a polychaete,pseudopotomilla occelata

Abstract

Receptor‐mediated endocytosis has been suggested for a stage‐specific transport mechanism of vitellogenin into the oocytes of a sabellid polychaete, Pseudopotamilla occelata. Membrane proteins of oocytes of three size classes, including small (30–70 μm in diameter), intermediate (70–140 μm in diameter) and large (180–200 μm in diameter), showed a stage‐specific variation. Coelomic fluid proteins (CP), assumed to be vitellogenin, consists of several proteins, which showed quite a different pattern from that of yolk proteins. Incorporation of 125I‐CP into the oocytes of the intermediate size class almost linearly increases with time, showing a contrast to the pattern of the large size class, in which the incorporation is low and approaches a plateau, suggesting the vitellogenin transports by a regulated process only in the intermediate size class. Vitellogenin receptor proteins were identified to be 60 kDa and 68 kDa only in the intermediate size class by a ligand blotting test.