Abstract
The pattern of nucleic-acid synthetic activity within the midgut cells of the silkworm larva (Bombyx mori L.) infected with midgut-nuclear-polyhedrosis virus was demonstrated in this paper by means of autoradiography with tritiated nucleic-acid precursors.
Autoradiographs of the diseased midgut treated with 3H-uridine revealed that at the early stage of infection a high grain density was found over the nucleus of the cylindrical cell, while the small amount of grain was scattered all over the cytoplasm. In the virus-infected cell, the nuclear label appeared most densely over the nucleolus, suggesting a large amount of RNA was synthesized there (Fig. 1). At the later stage of infection when large hexahedron polyhedra develop in the nucleus of the cylindrical cell, most of the autoradiographic grains were seen around the polyhedra (Figs. 2 and 3).
Autoradiographs with 3H-thymidine suggested that no essential difference in the pattern of DNA synthesis existed between the healthy and the virus-infected midguts: only a few regenerative as well as cylindrical cells incorporated 3H-thymidine into their nuclei. At the later stage of the virus infection, however, when most of the diseased cylindrical cells were eventually discharged into the gut lumen, autoradiographs of the midgut showed that the uptake of 3H-thymidine into the nucleus extremely increased in the regenerative cells and the newly developed cylindrical cells as well (Figs. 4, 5, and 6). This acceleration of DNA synthesis apparantly has no direct relation with the virus multiplication but is concerned with the regenerative development of cells.
Although in the midgut-nuclear polyhedrosis polyhedra only develop in the nuclei of midgut epithelial cells, the pattern of nucleic-acid synthesis in the virus-infected cell is much similar to that in the cytoplasmic-polyhedrosis which has been reported previously.
