Synthesis and secretion of egg-specific protein from follicle cells of the silkworm, Bombyx mori

The synthesis and secretion of egg-specific protein (ESP) were investigated using the follicle cells isolated from the developing ovary of the silkworm, Bombyx mori. The follicle cells were isolated manually from a follicle into a cell layer by thoroughly extruding the oocyte contents through a small hole. Whole follicles and isolated follicle cells were incubated in vitro with [³⁵S]methionine, and ESP and its precursors were immunochemically isolated using antiserum raised to ESP. The isolated follicle cells incorporated label into ESP but the incorporation rate was about one-fifth of that found in whole follicles. About 20% of the total radioactivity of ESPs were recovered from the incubation medium of the isolated follicle cells while only trace activity (<2%) was found in the incubation medium of whole follicles. These results clearly showed that follicle cells synthesize and release ESP to be taken up by the developing oocyte.