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

Large extrusion bodies (EBs) in Tetrahymena thermophila were induced by treatment with aphidiocolin (APH), followed by transfer of the cells to a drug free medium. APH induces over-replication of DNA and reversible cell division arrest (Kaczanowski and Kiersnowska, 2011). After treatment the cells were transferred to a drug free medium, and a central granule of chromatin (a prospective EB) surrounded by microtubules developed inside the macronucleus. Subsequently the chromatin of the central granule appeared in the middle region of the dividing macronucleus, and it was later extruded as an EB. The remaining chromatin segregated to opposite ends of the elongating macronucleus and was separated from the chromatin destined for the EB by intramacronuclear microtubules. TUNEL assay (terminal deoxynucleotidyl transferase dUTP nick end labeling]) and in vivo acridine orange (AO) staining showed that the EBs underwent apoptotic-like degradation and autophagy similar to that observed in programmed nuclear death (PND) of the old macronucleus in conjugant cells. Overall, based on the data obtained in this study we proposed the hypothesis that over- replication of DNA induced by APH results in the appearance of defective DNA copies, that are not segregated to the opposite regions of dividing macronucleus and are destined for EBs.