Temporal Dynamics of HCMV Gene Expression in Lytic and Latent Infections

Abstract Primary infection with Human cytomegalovirus (HCMV) results in a persistent lifelong infection due to its ability to establish latent infection. During productive HCMV infection, viral genes are expressed in a coordinated cascade that is characteristic of all herpesviruses and traditionally relies on the dependencies of viral genes on protein synthesis and viral DNA replication. In contrast, the transcriptional landscape associated with HCMV latency is still disputed and poorly understood. Here, we examine viral transcriptomic dynamics during the establishment of both productive and latent HCMV infections. These temporal measurements reveal that viral gene expression dynamics along productive infection and their dependencies on protein synthesis and viral DNA replication, do not fully align. This illustrates that the regulation of herpesvirus genes does not represent a simple sequential transcriptional cascade and surprisingly many viral genes are regulated by multiple independent modules. Using our improved classification of viral gene expression kinetics in conjunction with transcriptome-wide measurements of the effects of a wide array of chromatin modifiers, we unbiasedly show that a defining characteristic of latent cells is the unique repression of immediate early (IE) genes. In particular, we demonstrate that IE1 (a central IE protein) expression is the principal barrier for achieving a full productive cycle. Altogether, our findings provide an unbiased and elaborate definition of HCMV gene expression in lytic and latent infection states.