Intranuclear foci containing low abundance herpes simplex virus latency-associated transcripts visualized by non-isotopic in situ hybridization.

During latent infection of neurons with herpes simplex virus type 1 (HSV-1), several RNA transcripts of varying abundance arise from a single locus within the virus repeats. The functions of latency-associated transcripts (LATs) are unknown and the relationship between the various RNA species requires further clarification. Reported here is a novel approach to the study of HSV transcripts during latency, based on the increasing realization that cellular and viral RNAs are synthesized and processed by macromolecular complexes that occupy discrete compartments within the nucleoplasm of a cell. High resolution non-isotopic in situ hybridization was used to study the intranuclear topology of HSV-1 LATs in primary sensory neurons of latently infected mice and humans. Low abundance (minor) LATs were localized to sharply defined intranuclear foci of 1 to 3 microns in diameter. On average, there were 2.6 to 2.8 foci/LAT+ neuronal profile (5 microns), representing 13 to 14 foci/cell. In contrast to the focal deployment of minor LATs, the more abundant latency-associated RNAs were distributed diffusely throughout the nucleoplasms of latency infected neurons, with prominent sparing of nucleolar regions. These data establish a foundation for studying the synthesis, processing and transport of LATs in vivo. It should now be possible to investigate the nature of those cellular products which associate with HSV-1 encoded LATs in vivo and thereby determine whether minor LATs are associated with previously characterized macromolecular complexes, such as those responsible for processing of pre-messenger RNA.