Regulation of adenovirus alternative RNA splicing correlates with a reorganization of splicing factors in the nucleus.

Subcellular compartmentalization of splicing factors has been proposed to play a role in the regulation of alternative splicing. In the present work we have addressed this issue using adenovirus-infected cells to visualize an alternative splicing switch at the single cell level. The adenovirus gene expression program requires the activation of distal alternative 3' splice sites during the late phase of infection in major late transcripts. We have established in situ hybridization conditions that allow for the specific detection of 3' alternatively spliced adenoviral mRNAs from the L1 transcript family. Results show that the switch from proximal to distal 3' splice sites correlates with a massive reorganization of splicing factors in the cell nucleus, involving their recruitment from nuclear speckles to sites of viral transcription. This observation raises the possibility that the subnuclear organization of splicing factors may be regulated in response to events that lead to the activation of alternative splicing programs.