Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
10926637 | Cell Calcium | 2005 | 9 Pages |
Abstract
Ca2+-dependent contractility was found to exist in the nucleus of the heliozoon protozoan Actinophrys sol. Upon addition of Ca2+ ([Ca2+]free = 2.0 Ã 10â3 M), diameters of isolated and detergent-extracted nuclei became reduced from 16.5 ± 1.7 μm to 11.0 ± 1.3 μm. The threshold level of [Ca2+]free for the nuclear contraction was 2.9 Ã 10â7 M. The nuclear contraction was not induced by Mg2+, and was not inhibited by colchicine or cytochalasin B. Contracted nuclei became expanded when Ca2+ was removed by EGTA; thus cycles of contraction and expansion could be repeated many times by alternating addition of Ca2+ and EGTA. The Ca2+-dependent nuclear contractility remained even after high salt treatment, suggesting a possible involvement of nucleoskeletal components in the nuclear contraction. Electron microscopy showed that, in the relaxed state, filamentous structures were observed to spread in the nucleus to form a network. After addition of Ca2+, they became aggregated and constructed a mass of thicker filaments, followed by re-distribution of the filaments spread around inside of the nucleus when Ca2+ was removed. These results suggest that the nuclear contraction is induced by Ca2+-dependent transformation of the filamentous structures in the nucleus.
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Authors
Mikihiko Arikawa, Akira Saito, Gen Omura, S.M. Mostafa Kamal Khan, Yasutaka Suetomo, Soichiro Kakuta, Toshinobu Suzaki,