title: Ca2+-dependent nuclear contraction in the heliozoon Actinophrys sol.
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 x 10(-3) M), diameters of isolated and detergent-extracted nuclei became reduced from 16.5+/-1.7 microm to 11.0+/-1.3 microm. The threshold level of [Ca2+]free for the nuclear contraction was 2.9 x 10(-7) 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.
authors.affiliation: Department of Biological Sciences, Faculty of Science, Nara Women's University, Kitauoyanishi-machi, Nara 630-8506, Japan. miki_arkw1974@ybb.ne.jp
authors.forename: Mikihiko
authors.initials: M
authors.lastname: Arikawa
authors.forename: Akira
authors.initials: A
authors.lastname: Saito
authors.forename: Gen
authors.initials: G
authors.lastname: Omura
authors.forename: S M
authors.initials: SM
authors.lastname: Mostafa Kamal Khan
authors.forename: Yasutaka
authors.initials: Y
authors.lastname: Suetomo
authors.forename: Soichiro
authors.initials: S
authors.lastname: Kakuta
authors.forename: Toshinobu
authors.initials: T
authors.lastname: Suzaki
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002467:Cell Nucleus / Q000187:drug effects* / Q000648:ultrastructure; D004533:Egtazic Acid / Q000494:pharmacology; D056890:Eukaryota / Q000648:ultrastructure*; D008854:Microscopy, Electron; D015530:Nuclear Matrix / Q000187:drug effects*
chemical_list: D004533:Egtazic Acid; D002118:Calcium