Ca2+-dependent nuclear contraction in the heliozoon Actinophrys sol.
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.
Arikawa
Mikihiko
M
Department of Biological Sciences, Faculty of Science, Nara Women's University, Kitauoyanishi-machi, Nara 630-8506, Japan. miki_arkw1974@ybb.ne.jp
Saito
Akira
A
Omura
Gen
G
Mostafa Kamal Khan
S M
SM
Suetomo
Yasutaka
Y
Kakuta
Soichiro
S
Suzaki
Toshinobu
T
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*
D004533:Egtazic Acid; D002118:Calcium