Data from: Primary envelopment of Kaposi’s sarcoma-associated herpesvirus at the nucleoplasmic reticulum

Herpesvirus egress begins with primary envelopment of newly assembled
capsids at the inner nuclear membrane (INM). Primary envelopment has been
observed at the peripheral INM as well as nuclear infoldings. Nuclear
infoldings from invaginations of the INM are Type-I nucleoplasmic
reticulum (NR), whereas infoldings of both INM and outer nuclear membrane
(ONM) are Type-II NR. Here, we report that Kaposi’s sarcoma-associated
herpesvirus (KSHV) reactivation from latency and lytic cycle progression
correlates with increases in both types of NR, but primary envelopment is
restricted to peripheral INM and Type-I NR. These Type-I NR structures
co-localized with puncta containing CTP:phosphocholine
cytidylyltransferase (CCTα), the enzyme that catalyzes the rate-limiting
step in phosphatidylcholine (PtdCho) synthesis that drives the de novo
membrane biogenesis and membrane curvature required for NR expansion; CCTα
recruitment may provide sufficient Type-I NR to facilitate nuclear egress.
Despite the concurrent expansion of Type-II NR, primary envelopment
involves a mechanism that specifically targets capsids to Type-I NR.
Building upon our observation of capsids lacking envelopes in complex
higher-order Type-I NR structures, we used polar lipid dyes, CLICK-labeled
fluorescent viral genomes, and fluorescent KSHV capsids to track the fate
of NR-associated capsids via live cell microscopy. These studies provide
evidence for trafficking of NR-associated capsids toward the nuclear
periphery and cytoplasm. Taken together, these findings suggest that
nuclear egress occurs not only at the nuclear periphery but also at the
Type-I NR.