Extrusion of Nuclear Materials into Cytoplasm in the Posterior Silk Gland Cells of Silkworm, Bombyx Mori

The transfer of microscopically visible material from the nucleus into the cytoplasm has been described from time to time for many years (1). Application of electron microscopic techniques to the study of nucleocytoplasmic interactions has made it clear that several methods may exist by which materials or substances are transported between the nucleus and cytoplasm (2). The pores or annuli of the nuclear envelope appear to represent, in most cases, main sites of nucleocytoplasmic exchange (3-5). Further, a variety of blebs and outpocketings of the nuclear envelope have been suggested to represent a morphological stage in the transfer of nuclear material to cytoplasm (6, 7, 2). While studying the ultrastructure of the cells of posterior silk gland during the fourth and fifth larval instars, we have had a chance to observe the partial disappearance of the nuclear envelope and the subsequent extrusion of the nuclear materials directly into cytoplasm.