Formation and degradation of large extrusion bodies in Tetrahymena thermophila: The role of intramacronuclear microtubules in chromatin segregation

Disruption of a ∼23–24 nucleotide small RNA pathway elevates DNA damage responses in Tetrahymena thermophila

“…, 1992 ; Gao et al. , 2013 ; Kaczanowski and Kiersnowska, 2018 ). Indeed, although only ∼2–3% of cells in asynchronous cultures are in amitosis (Supplemental Figure S1, B–D), we found MAC DNA distribution to daughter cells often lags behind the formation of cytokinetic furrows in RSP1 Δ and RDN2 Δ compared to SB210, as illustrated by the representative dividing cells outlined in Figure 2A .…”

“…, 1992 ; Wiley et al. , 2005 ; Kaczanowski and Kiersnowska, 2018 ). However, hallmarks of DNA damage have also been found in some CEBs, even as they form ( Gao et al.…”

“…, 2006 ; Gao et al. , 2013 ; Kaczanowski and Kiersnowska, 2018 ), depletion of condensin or histone deacetylase Thd1 ( Wiley et al. , 2005 ; Cervantes et al.…”

“…These DAPI-staining bodies were typically well separated from the MAC and did not stain with a mitotic MIC marker, which distinguishes them from MIC nuclei as MICs closely associate with MACs when not in mitosis. These are likely chromatin extrusion bodies (CEBs), which are thought to arise from MAC DNA failing to segregate during amitosis and may ultimately fragment in a TUNEL-positive process (Bodenbender et al, 1992;Gao et al, 2013;Kaczanowski and Kiersnowska, 2018). Indeed, although only ~2-3% of cells in asynchronous cultures are in amitosis (Supplemental Figure S1B-D), we found MAC DNA distribution to daughter cells often lags behind the formation of cytokinetic furrows in RSP1 and RDN2 compared to SB210, as illustrated by representative dividing cells outlined in Figure 2A.…”

“…Micronuclei contain whole chromosomes or acentric fragments of chromosomes and are formed when DNA is mis-segregated as a result of errors in DNA replication, DNA repair, chromosome segregation and cell cycle checkpoints (Guo et al, 2019). Similarly, Tetrahymena CEB frequency and size increases with disruptions to normal DNA replication (Morrison et al, 2005;Yakisich et al, 2006;Gao et al, 2013;Kaczanowski and Kiersnowska, 2018), depletion of condensin or histone deacetylase Thd1 (Wiley et al, 2005;Cervantes et al, 2006a), or blocks to DNA repair (Marsh et al, 2000;Song et al, 2007). Based on a positive correlation observed between MAC DNA content and CEB production, it has been speculated that production of CEBs may be a mechanism to selectively eliminate extra copies of MAC chromosomes that are aberrantly replicated and/or result from imbalances in amitotic MAC division (Cleffmann, 1980;Bodenbender et al, 1992;Wiley et al, 2005;Kaczanowski and Kiersnowska, 2018).…”