Session Item

Micronuclei (MN) are small DNA structures in the cytoplasm that arise from DNA fragments or whole chromosomes that remain distinct from the main nucleus after DNA damage. Recent evidence has found that MN can become repositories for the pattern recognition receptor cyclic GMP-AMP synthase (cGAS) that drives activation of stimulator of interferon genes (STING) and cytokine signalling. Despite their recognized importance to radiobiology few studies have focused on the functional properties of MN and their role as organizing centres of cellular signalling. In this work we explore molecular features of MN that emerge from different forms of DNA damage, especially ionizing radiation, and ask how these features associate with cGAS recruitment and activation of cytokine transcription.

Using established cell lines (MCF10A, HeLa-S3 and U2OS) treated with multiple DNA damaging agents (ionizing radiation (IR), methyl methanesulfonate, hydroxyurea, etc.) we profile cGAS recruitment and transcription in MN using immunofluorescence. In a small molecule screen, we ask how histone modifying enzymes influence MN properties and the recruitment of cGAS to MN.

We find that heterogeneous recruitment of cGAS to MN is determined by the type of DNA damage that leads to MN formation. Rupture of the MN envelope is necessary but not sufficient for recruitment of cytosolic cGAS. Instead, we find that nuclear chromatin status at the time of DNA damage induction and MN formation is a primary determinant of cGAS localization and subsequent cytokine signalling through the cGAS-STING pathway.

DNA damage induced MN are not monolithic. Heterogeneity in MN properties emerges because of the nuclear chromatin state at the time of DNA damage. Together our findings begin to uncover the unique place of MN in cellular signalling and argue for their role as central integrators of the cellular response to DNA damages.