Acquisition of the Envelope of Nuclear Polyhedrosis Viruses in the Chinese Oak Silkworm, Antheraea pernyi GUER-MIN, and the Japanese Giant Silkworm, Dictyoploca japonica BUTLER

Abstract

The envelopment processes of nuclear polyhedrosis viruses (NPV's) infected in the fat body cells of the Chinese oak silkworm, Antheraea pernyi GUER-MIN, and the Japanese giant silkworm, Dictyoploca japonica BUTLER, were examined by electron microscopy. After assembly in the infected nuclei, the most of naked nucleocapsids were enclosed with envelopes formed by de novo morphogenesis. However, some naked nucleocapsids were wrapped with the inner nuclear membrane by budding after the membrane became thicker and dense at the point of contact with them. The nucleocapsids wrapped by this way were lying free in the perinuclear cisterna. In the cytoplasm, some naked nucleocapsids were also observed at the earlier stage of virus replication. They appeared to acquire their envelopes from the plasma membrane also by budding. From the above observations, the modes of envelopment of NPV's are tentatively classified into three ways; 1) de novo morphogenesis, 2) nuclear budding and 3) cytoplasmic budding. After completion of the nuclear and cytoplasmic buddings, the wrapped nucleocapsids seemed to emerge "actively" from the infected fat body cells into hemocoel; these envelopments occurred at early stages of virus replication before polyhedron formation, being followed by nucleo- or cytolysis.