dictyNews
Electronic Edition
Volume 35, number 3
July 16, 2010
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Abstracts
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A fully resolved phylogeny of the social amoebas (Dictyostelia) based
on combined ncSSU and ITS rDNA Sequences
Romeralo, M. Spiegel, F.W. & Baldauf, S.
Protist (online 2010)
The dictyostelids possess a complex life cycle including aggregative
and multicellular stages. They also include one of the most widely
studied protistan model organisms, Dictyostelium discoideum. The
current molecular phylogeny of dictyostelids is based largely on
SSU(18S) rDNA sequences and shows a deep taxon consisting of
four major groups, none of which correspond to the three traditional
morphologically-defined genera. However, due to the generally slowly
evolving nature of SSUrDNA, these data fail to resolve the majority of
branches within the four groups. Given the highly morphologically mixed
nature of the dictyostelid groups, it is important to resolve
relationships
within them. We have determined sequences for the internal transcribed
spacers (ITS) of rDNA for nearly all species in the original
dictyostelid
global phylogeny. Phylogenetic analyses of these data, in combination
with the previously determined SSUrDNA sequences, confidently resolve
nearly all branches in the tree. This now fully resolved phylogeny
confirms
the utility of ITS for dictyostelid systematics and lays the ground
work for
further evolutionary study of the group.
Submitted by Maria Romeralo [[log in to unmask]]
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Dynamics of a novel centromeric histone variant CenH3 reveals the
evolutionary ancestral timing of centromere biogenesis
Manu Dubin*, Jörg Fuchs†, Ralph Gräf‡, Ingo Schubert†, Wolfgang
Nellen*,§.
*Department of Genetics, University Kassel, Heinrich-Plett-Str. 40,
34132 Kassel, Germany
†Leibniz-Institute of Plant Genetics and Crop Plant Research (IPK),
Corrensstrasse 3, 06466 Gatersleben, Germany
‡Department of Cell Biology, Institute for Biochemistry and Biology,
University of Potsdam, Potsdam-Golm, Germany.
Nucleic Acids Res., in press
The centromeric histone H3 variant (CenH3) serves to target the
kinetochore
to the centromeres and thus ensures correct chromosome segregation
during
mitosis and meiosis. The Dictyostelium H3-like variant H3v1 was
identified
as the CenH3 ortholog. Dictyostelium CenH3 has an extended N-terminal
domain with no similarity to any other known proteins and a histone fold
domain at its C-terminus. Within the histone fold, alpha-helix 2
(alpha2)
and an extended loop 1 (L1) have been shown to be required for targeting
CenH3 to centromeres. Compared to other known and putative CenH3
histones, Dictyostelium CenH3 has a shorter L1 suggesting that the
extension is not an obligatory feature. Through ChIP analysis and
fluorescence microscopy of live and fixed cells we provide here the
first
survey of centromere structure in amoebozoa. The six telocentric
centromeres were found to mostly consist of all the DIRS-1 elements
and to associate with H3K9me3. During interphase the centromeres
remain attached to the centrosome forming a single CenH3 containing
cluster. Loading of Dictyostelium CenH3 onto centromeres occurs at the
G2/prophase transition, in contrast to the anaphase/telophase loading of
CenH3 observed in metazoans. This suggests that loading during
G2/prophase is the ancestral eukaryotic mechanism and that
anaphase/telophase loading of CenH3 has evolved more recently
after the amoebozoa diverged from the animal linage.
Submitted by Wolfgang Nellen [[log in to unmask]]
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[End dictyNews, volume 35, number 3]
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