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Protistology ■ 53
Two epigenetic phenomena occur in crosses of Paramecium tetraurelia strains 32 and 51. Strain 32 is deficient for an IES present in one of the mating type genes, mtB, of strain 51. Internal eliminated sequences are excised from the developing macro-nuclear genome by a fascinating mechanism of genomic subtraction mediated by scanRNAs. However, if an IES is present in genome of one partner but absent in genome of another, then F1 hybrids deriving from the latter parent are unable to excise such IES from developing somatic genome: they can't produce a certain scanRNA. Moreover, F2 progeny of such cell will inherit this IES retained in macronucleus. IES inside a gene disrupts its function, thus reminding hybrid dysgenesis known for Drosophila. Indeed, in 25% of crosses we observed loss of mtB function in F2 progeny derived from parent 32. We also found unexpectedly that in 20% of crosses IES in mtB gene was retained in macronucleus of F2 progeny derived from parent 51, which normally produces scanRNAs and excises this IES. Analogous phenomenon was reported in cross of d12 and d48 deletion mutants of P. tetraurelia restoring functional gene of surface antigen A. We suggest that its mechanism may be connected with hemizygocity state ofthe deleted locus in F1 hybrids of such crosses, leading somehow to deviation of such sequence excision despite scanRNAs for it are present. These epigenetic effects may contribute into speciation in ciliates, as occasional hemizygocity may lead to lethality of interstrain hybrids. Supported by RFBR 16-04-01710.
RECONSTRUCTION OF CELLULAR SHAPE DEFORMATION THROUGH CONTRACTION OF CORTEX ACTOMYOSIN Nishigami Yukinori1, Ito Hiroaki2, Sonobe Seiji3, Ichikawa Masatoshi1
1 - Department of Physics, Graduate School ofScience, Kyoto University, Kyoto 606-8502, Japan
2 - Department ofMechanical Engineering, Graduate School ofEngineering, Osaka University, Osaka 5650871, Japan
3 - Department of Life Science, Graduate School of Life Science, University of Hyogo, Harima Science Park City, Hyogo 678-1297, Japan [email protected]
Giant free-living amoebae, Amoeba proteus, actively deform cellular shape during the locomotion. The deformation is induced by contraction of cortical actin and myosin (actomyosin). In the process, since actomyosin is connected to the cellar membrane and transmit the generated force to deform the membrane. Although the contractile properties of
actomyosin networks have been reported, actual contributions to the membrane deformation are still unclear because of the cellular complexities. Here, in order to simplify the complex system, we attempted to reconstitute a simple model system, in which lipid monolayer was deformed by actomyosin. In living cells, the connection between actomyosin and lipid layer is achieved by various types of proteins. To simply accomplish the actin-membrane connection in vitro, we adapted positively-charged lipid DOTAP (1,2-dioleoyl-3-trimethylammonium-propane), expecting the electrostatic adhesion between negatively-charged actin and DOTAP. We extracted actomyosin from A. proteus and enclosed actomyosin fraction within a spherical space surrounded by a DOTAP monolayer. As a result, active deformation ofthe lipid monolayer was yielded. From analyses ofthe static and dynamic properties of the deformation, we found that the depth and width ofthe deformation were dependent on the curvature radius of the sphere. The observed curvature dependence is explained by the theoretical description including elasticity and contractility of the cortex. Our results provide a fundamental insight into the cellular membrane deformation induced by the actomyosin cortex during amoeboid locomotion. For more details, see Nishigami et al. (Sci. Rep. 6, 19864, 2016) and Ito, Nishigami et al. (Phys. Rev. E92,062711,2015).
NUCLEAR DIVISION PROCESS IN TESTATE AMOEBA PAULINELLA CHROMATOPHORA Nomura M., Ishida K.
Faculty ofLife and Environmental Sciences, University of Tsukuba
Paulinella chromatophora is a euglyphid testate amoeba (Rhizaria, Cercozoa) living in a shell composed of ~50 rectangular siliceous scales. In this species, the complex shell construction process appears to be integrated under the cell cycle regulation, since the cell division does not proceed without the completion of shell construction. Before cell division, scales produced inside of mother cell are secreted out from the cell and assembled into a new shell by a specialized thick pseudopodium. Following the completion of shell construction, one of daughter cells moves into the new shell. Despite that knowledge, it is still unknown how the cell division process proceeds in response to the shell construction. In this study, we focused on how the nucleus divides along with shell construction process in P. chromatophora. In an intermediate stage of shell construction, the nucleus in the maternal cell was in prophase. In this phase, the nucleolus, which
