Abstract
Herpesviruses are composed of capsid, tegument, and envelope. Capsids assemble in the nucleus and exit the
nucleus by budding at the inner nuclear membrane, acquiring tegument and the envelope. This study focuses
on the changes of the nuclear envelope during herpes simplex virus 1 (HSV-1) infection in HeLa and Vero cells
by employing preparation techniques at ambient and low temperatures for high-resolution scanning and
transmission electron microscopy and confocal laser scanning microscopy. Cryo-field emission scanning
electron microscopy of freeze-fractured cells showed for the first time budding of capsids at the nuclear
envelope at the third dimension with high activity at 10 h and low activity at 15 h of incubation. The mean
number of pores was significantly lower, and the mean interpore distance and the mean interpore area were
significantly larger than those for mock-infected cells 15 h after inoculation. Forty-five percent of nuclear pores
in HSV-1-infected cells were dilated to more than 140 nm. Nuclear material containing capsids protrude
through them into the cytoplasm. Examination of in situ preparations after dry fracturing revealed significant
enlargements of the nuclear pore diameter and of the nuclear pore central channel in HSV-1-infected cells
compared to mock-infected cells. The demonstration of nucleoporins by confocal microscopy also revealed
fewer pores but focal enhancement of fluorescence signals in HSV-1-infected cells, whereas Western blots
showed no loss of nucleoporins from cells. The data suggest that infection with HSV-1 alters the number, size,
and architecture of nuclear pores without a loss of nucleoporins from altered nuclear pore complexes.
Wild, P