Chromatin extrusion in resting encystment of Colpoda cucullus: A possible involvement of apoptosis‐like nuclear death

Abstract

The extrusion of macronuclear chromatin is a remarkable characteristic during encystment in Colpoda, but the biological significance of this phenomenon has not been fully elucidated. Here we demonstrate that chromatin extrusion occurs with high frequency when encystment was induced by increasing Ca(2+) in growing cells in various stages of the cell cycle. The Feulgen-DNA reaction revealed that vegetatively growing cells have more macronuclear DNA than cells in the stationary phase, suggesting an association of macronuclear DNA content with the execution of chromatin extrusion. Using 4',6-diamidino-2-phenylindole (DAPI), we found that the size of the macronuclear extrusion body was reduced with time and eventually disappeared approximately 24h after encystment induction. In addition, oligonucleosome-sized DNA cleavage was confirmed to occur concomitant with the size reduction, suggesting that the extrusion body is selectively degraded, while the normal macronucleus remains alive. Combined use of acridine orange and Hoechst 33342 demonstrated that the extruded body was increasingly acidified before final resorption. These features are reminiscent of the nuclear degradation process in conjugating Tetrahymena, and therefore we conclude that chromatin extrusion in Colpoda might occur to adjust the macronuclear DNA content prior to encystment. In this way, it is similar to the apoptotic-like nuclear death that occurs during the conjugation of other ciliates.

EF‐1α and Mitochondrial ATP Synthase β Chain: Alteration of their Expression in Encystment‐Induced Colpoda cucullus

“…), and thereafter a large mass of chromatin is often extruded from the macronucleus (Kidder and Claff ). The extruded chromatin mass is degraded by autophagy for 1–2 d (Akematsu and Matsuoka ; Funatani et al. ).…”

“…In 2-3 h after the onset of encystment induction, many small chromatin granules are extruded from the macronucleus to be digested in the cytoplasm (Funatani et al 2010), and thereafter a large mass of chromatin is often extruded from the macronucleus (Kidder and Claff 1938). The extruded chromatin mass is degraded by autophagy for 1-2 d (Akematsu and Matsuoka 2008;Funatani et al 2010). Mitochondrial membrane potential disappears in 7-15 h after the onset of encystment induction (Funatani et al 2010).…”

Role of apoptosis-inducing factor (AIF) in programmed nuclear death during conjugation in Tetrahymena thermophila

“…Therefore, AIF may be bifunctional, serving as both a vital protein and a death effector. Among ciliates, apoptosis-like nuclear degradation has been observed during resting cyst formation leading to change in macronuclear DNA content in Colpoda [29]. In this case, the macronuclear chromatin is extruded into the cytosol, and the degradation of the extrusion body is accompanied by a reduction in the size of the nucleus, oligonucleosome-size DNA cleavage, and nuclear acidification by lysosomes.…”

Culture Age, Intracellular Ca2+ Concentration, and Protein Phosphorylation in Encystment-Induced Colpoda cucullus

“…The vegetative cells of C. cucullus cultured in a cereal (wheat leaves) infusion containing bacteria have been shown to grow rapidly for 1-1.5 days; thereafter, the cells begin to encyst (spontaneous encystment) [8]. Our preliminary observation showed that it was difficult to induce rapidly growing cells to encyst, while post-growing cells were apt to encyst.…”