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dictyNews Volume 25 Number 03
Dicty News
Electronic Edition
Volume 25, number 3
August 5, 2005
Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to dicty@northwestern.edu
or by using the form at
http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit.
Back issues of Dicty-News, the Dicty Reference database and other
useful information is available at dictyBase - http://dictybase.org.
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Abstracts
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Social behaviour in genetically heterogeneous groups of
Dictyostelium giganteum
Sonia Kaushik, Bandhana Katoch and Vidyanand Nanjundiah
Indian Institute of Science
Bangalore
Behavioural Ecology & Sociobiology, in press
The Dictyostelid or cellular slime moulds (CSMs) are soil amoebae with an
asexual life cycle involving social behaviour and division of labour. The
most obvious distinction is between 'germ line'â or pre-spore cells, that
survive, and 'somatic'â or pre-stalk cells, that eventually die. A
plausible hypothesis to explain the apparent altruism of pre-stalk cells
is that it is directed at clonal relatives. We have tested this hypothesis
by comparing indices of altruistic behaviour between clonal and chimaeric
(genetically heterogeneous) social groups. The groups were generated by
mixing amoebae belonging to distinguishable strains of Dictyostelium
giganteum .The amoebae of one strain do not aggregate at all when mixed
with any of three other strains and aggregate poorly with a fourth. Among
the latter, co-aggregation occurs but is followed by varying extents of
sorting-out. At times two strains form separate fruiting bodies; in other
cases they remain together but are clustered in clonal groups within a
single chimaeric structure. Our expectation was that the allocation of
cells to the stalk pathway would be higher, and to the spore pathway
lower, in clonal social groups than in chimaeras. The expectation was not
always fulfilled. Also, three strains could be arrayed in a linear
rank-order in terms of the relative efficiencies of spore-formation in
binary mixtures, but when all three were mixed they were equally
efficient. More than overall genetic similarity, cell fate in a chimaera
seems to result from complex non-linear interactions based on epigenetic
differences.
Submitted by: Vidyanand Nanjundiah [vidya@ces.iisc.ernet.in]
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Prespore cell fate bias in G1 phase of the cell cycle in Dictyostelium
Guokai Chen and Adam Kuspa
Verna and Marrs McLean Department of Biochemistry and Molecular Biology,
and Department of Molecular and Human Genetics,
Baylor College of Medicine, One Baylor Plaza, Houston TX 77030.
Eukaryotic Cell, in press
By generating a population of Dictyostelium cells that are in the G1 phase
of the cell cycle we have examined the influence of cell cycle status on
cell fate specification, cell-type proportioning and its regulation and
terminal differentiation. We exploited the fact that spores encapsulate in
G1 to produce populations of G1-phase cells by germinating spores and
harvesting the emergent amoebae before they re-entered the cell cycle. The
lack of observable mitosis during the development of these cells and the
quantification of their cellular DNA content suggests that they remain
in G1 throughout development. Furthermore, chromosomal DNA synthesis was
not detectable these cells, indicating that no S phase had occurred,
although substantial mtDNA synthesis did occur in prespore cells. The
G1-phase cells underwent normal morphological development and sporulation,
but displayed an elevated prespore/prestalk ratio of 5.7 compared to the
3.0 ratio normally observed in populations dominated by G2-phase cells.
When migrating slugs produced by G1-phase cells were bisected, each half
could re-establish the 5.7 prespore/prestalk ratio. These results
demonstrate that Dictyostelium cells can carryout the entire developmental
cycle in G1 phase of the cell cycle, and that passage from G2 into G1 phase
is not required for sporulation. Our results also suggest that the population
asymmetry provided by the distribution of cells around the cell cycle at the
time of starvation is not strictly required for cell-type proportioning.
Finally, when developed together with G2-phase cells, G1-phase cells
preferentially become prespore cells and exclude G2-phase cells from the
prespore/spore cell population, suggesting that G1-phase cells have an
advantage over G2-phase cells in executing the spore cell differentiation
pathway.
Submitted by: Adam Kuspa [akuspa@bcm.tmc.edu]
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[End Dicty News, volume 25, number 3] 
