Canine parvovirus infection affects host cell nucleolar organization and ribosome biogenesis.

The nucleolus is a biomolecular condensate essential for ribosome biogenesis and cellular stress response, and it is a key target for many DNA viruses. However, little is known about how autonomous parvovirus infection impacts the nucleolus. Here, we used ten-fold robust expansion microscopy, cryo soft X-ray tomography, interactomics, and biochemical approaches to study nucleolar remodeling during canine parvovirus infection. The nucleolus is organised in nested layers. Infection led to redistribution of nucleolar upstream binding transcription factor 1 (inner core), fibrillarin (middle layer), and Ki-67 (outer rim). In contrast, peripheral nucleolar proteins (nucleolin and nucleophosmin) and precursor ribosomal RNAs remain in spherical structures. High-resolution microscopy revealed profound nucleolar structural changes, including thickened perinucleolar chromatin and enlarged nucleolar low-protein density channels. BioID identified interactions between viral NS2 and nucleolar proteins involved in ribosome biogenesis. Northern blotting demonstrated a slowdown in ribosome biogenesis during infection. Collectively, these findings provide insights into how parvoviruses remodel nucleolar structure and function.