Copy Link
Add to Bookmark
Report
dictyNews Volume 19 Number 07
Dicty News
Electronic Edition
Volume 19, number 7
September 21, 2002
Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to dicty@northwestern.edu.
Back issues of Dicty-News, the Dicty Reference database and other useful
information is available at DictyBase--http://dictybase.org.
=============
Abstracts
=============
Electron microscopy of actin rods and bundles in Dictyostelium discoideum by
high-pressure freezing
Masazumi Sameshima1*, Yoshiro Kishi1, Masako Osumi2, Dana Mahadeo3, and David
A. Cotter3
1Electron Microscopy Center, The Tokyo Metropolitan Institute of Medical
Science, Tokyo Metropolitan Organization for Medical Research, 3-18-22
Honkomagome, Bunkyo-ku, Tokyo 113-8613, Japan, 2Department of Chemical and
Biological Sciences, Faculty of Science, Japan Women's University, Bunkyo-ku,
Tokyo 112-8681, Japan, and 3Department of Biological Sciences, University of
Windsor, Windsor, Ontario N9B 3P4, Canada
J Electron Microscopy, in press.
Abstract
A new type of actin rods comprising actin tubules appear in dormant spores
of Dictyostelium discoideum. A combination of high-pressure freezing and
freeze-substitution (high-pressure freezing) is an effective method for
analyzing structures of the actin rods appeared. However, the rods in the
nucleus were occasionally observed in an amorphous state using this method.
Also in the case of actin bundles formed in the nucleus of vegetative cells
exposed to dimethyl sulfoxide, actin filaments seemed to be embedded in
matrices. The karyoplasm of spores fixed by high-pressure freezing appeared
to be denser than that obtained by other methods. Soluble materials may be
efficiently retained in the nucleus, and so actin tubules or actin filaments
embedded in those materials may result in hazy images of actin rods and
bundles.
-----------------------------------------------------------------------------
The costs and benefits of being a chimera
Kevin R Foster, Angelo Fortunato, Joan E Strassmann and David C Queller
Department of Ecology and Evolutionary Biology, Rice University MS 170
6100 Main, Houston Texas, 77005 USA
Proceedings of the Royal Society, Series B, in press.
Summary
Most multicellular organisms are uniclonal. This is hypothesized to be
because uniclonal organisms function better than chimeras (non-clonal
organisms), due to reduced levels of internal genetic conflict. We tested
this idea using the social amoeba Dictyostelium discoideum. When starving,
the normally solitary amoebae aggregate to form a differentiated
multicellular slug that migrates towards light and forms a fruiting body,
facilitating the dispersal of spores. We added 107 amoebae to petri plates
containing 1, 2, 5 or 10 clones mixed together. We found an intrinsic cost
to chimerism: chimeric slugs moved significantly less far than uniclonal
slugs of the same size. However, in nature joining with other clones to
form a chimera should increase slug size, and larger slugs travel farther.
We incorporated this size effect into a second experiment by giving chimeras
more cells than single clones (uniclonal got 106 cells, 2-clone chimeras got
2x106 cells and so on). The uniclonal treatments then simulated a clone in a
mixture that refuses to form chimeras. In this experiment, chimeras moved
significantly further than the uniclonal slugs, in spite of the intrinsic
cost. Thus, chimerism is costly, which may be why it evolves so seldom,
but in D. discoideum the benefits of large size appear to compensate.
-----------------------------------------------------------------------------
[End Dicty News, volume 19, number 7]
