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Reconstruction of cellular shape deformation through contraction of cortex actomyosin.

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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 macronuclear 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 of the 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.
Nishigami Yukinori1, Ito Hiroaki2, Sonobe Seiji3,
Ichikawa Masatoshi1
- Department of Physics, Graduate School of Science,
Kyoto University, Kyoto 606-8502, Japan
- Department of Mechanical Engineering, Graduate
School of Engineering, Osaka University, Osaka 5650871, Japan
- Department of Life Science, Graduate School of
Life Science, University of Hyogo, Harima Science
Park City, Hyogo 678-1297, Japan
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
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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-dioleoyl3-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 of the lipid monolayer
was yielded. From analyses of the static and dynamic
properties of the deformation, we found that the
depth and width of the 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.
E 92, 062711, 2015).
Nomura M., Ishida K.
Faculty of Life 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
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deformation, actomyosin, contractile, corte, shape, cellular, reconstruction
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