Formation of Transport Coated Pits and Vesicles Uniquely Stimulated by Exogenous Yolk Proteins in in vitro Oocytes

Abstract

We have characterized several systems that exhibit selective protein sequestration in order to use them as model systems to elucidate the mechanisms of specific protein endocytosis. One of these, the mosquito ovary, is ideal because it contains synchronous oocytes and is easily cultivated in vitro. To date we have characterized the yolk proteins, established that the oocytes selectively sequester yolk proteins and that the oocytes effectively exclude other proteins. The transport exhibits saturation kinetics typical of active transport and is inhibitable.To establish the morphological basis of this selection, we incubated ovaries that had been previously active in laying down yolk (24 hr post blood meal) in an in vitro culture with either yolk protein, ferritin, IgG, albumin, or a combination of these proteins. We confirmed earlier observations that significant transport occurs only in the presence of yolk proteins.