Abstract
The patterns of nucleic-acid synthetic activity within the midgut cells of healthy silkworm larva (Bombyx mori L.) and of larvae infected with the cytoplasmic- and nuclear-polyhedrosis viruses as well as flacherie virus were demonstrated by means of autoradiography with tritiated nucleic-acid precursors.
Autoradiographs with 3H-thymidine revealed no essential difference in the pattern of DNA synthesis between healthy and cytoplasmic-polyhedrosis midguts, and only a few cells incorporated the labeled material into their nuclei (Figs. 1 and 3). At the late stage of the virus infection, however, when some infected midgut cells eventually degenerated, there was a slight increase in the nuclear label in the newly regenerated cells (Fig. 4). On the other hand, in the nuclear-polyhedrosis midgut, hypertrophic nuclei of cylindrical cells as well as goblet cells were densely labeled with 3H-thymidine without accompanying any formation of polyhedra (Fig. 9). In the midgut infected with flacherie virus, most of the cylindrical cells incorporated much of 3H-thymidine into their nuclei during the course of the disease, while no detectable radioactivity was seen on the goblet cells (Figs. 11, 12, and 13).
At five hours after injection of 3H-uridine, the healty cells generally incorporated the labeled material into cytoplasmic RNA and partly into nuclear RNA (Fig. 2), whereas in the cytoplasmicpolyhedrosis midgut the diseased cells incorporated much of the labeled uridine into nuclear RNA and some into cytoplasmic RNA. In the nuclei of the virus-infected cells, the nuclear label appeared most densely over the nucleoli (Figs. 5, 6, 7, and 8). In the nuclear-polyhedrosis midgut, however, the incorporation of 3H-uridine into both nuclear and cytoplasmic RNA was slightly larger than that in the healthy one (Fig. 10). In the early stage of flacherie-virus infection, both cylindrical and goblet cells incorporated a great amount of 3H-uridine into their nuclei and some into the cytoplasm (Fig. 14), while at the late stage of infection degenerating goblet cells stilll actively incorporated the labeled material into their nuclei and most of the label seemed to diffuse to be accumulated in the cytoplasm around the goblet (Fig. 15 and 16).
