dictyNews
Electronic Edition
Volume 38, number 24
September 21, 2012
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Abstracts
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PIP3 waves and PTEN dynamics in the emergence of cell polarity
Guenther Gerisch1*, Britta Schroth-Diez2, Annette Mueller-Taubenberger3,
and Mary Ecke1
1Max Planck Institute of Biochemistry, 82152 Martinsried, Germany;
2Max Planck Institute of Molecular Cell Biology and Genetics, 01307
Dresden, Germany; and 3Ludwig Maximilian University of Munich,
Institute for Cell Biology, 80336 Muenchen, Germany
*Correspondence: [log in to unmask]
Biophysical Journal, Volume 103, September 2012 1-9
In a motile eukaryotic cell, front protrusion and tail retraction are
superimposed on each other. In order to single out mechanisms that
result in front to tail or in tail to front transition, we separated the two
processes in time using cells that oscillate between a "full front"and a
"full tail" state. State transitions were visualized by total internal reflection
fluorescence microscopy using as a front marker PIP3 (phosphatidyl
inositol [3,4,5] tris-phosphate), and as a tail marker the tumor-suppressor
PTEN (phosphatase tensin homologue) that degrades PIP3. Negative
fluctuations in the PTEN layer of the membrane gated a local increase in
PIP3. In a subset of areas lacking PTEN ("PTEN holes"), PIP3 was
amplified until a propagated wave was initiated. Wave propagation implies
that a PIP3 signal is transmitted by a self-sustained process, such that the
temporal and spatial profiles of the signal are maintained during passage
of the wave across the entire expanse of the cell membrane. Actin clusters
were remodeled into a ring along the perimeter of the expanding PIP3 wave.
The reverse transition of PIP3 to PTEN was linked to the previous site of
wave initiation: where PIP3 decayed first, the entry of PTEN was primed.
Submitted by Guenther Gerisch [[log in to unmask]]
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Whole Genome Sequencing of Mutation Accumulation Lines Reveals a
Low Mutation Rate in the Social Amoeba Dictyostelium discoideum
Gerda Saxer, Paul Havlak, Sara A. Fox, Michael A. Quance, Sharu Gupta,
Yuriy Fofanov, Joan E. Strassmann, David C. Queller
PLoS ONE, in press
Spontaneous mutations play a central role in evolution. Despite their
importance, mutation rates are some of the most elusive parameters to
measure in evolutionary biology. The combination of mutation
accumulation (MA) experiments and whole-genome sequencing now
makes it possible to estimate mutation rates by directly observing new
mutations at the molecular level across the whole genome. We performed
an MA experiment with the social amoeba Dictyostelium discoideum and
sequenced the genomes of three randomly chosen lines using
high-throughput sequencing to estimate the spontaneous mutation rate
in this model organism. The mitochondrial mutation rate of 6.76x10^-9,
with a Poisson confidence interval of 4.1x10^-9 - 9.5x10^-9, per nucleotide
per generation is slightly lower than estimates for other taxa. The mutation
rate estimate for the nuclear DNA of 2.9x10^-11, with a Poisson confidence
interval ranging from 7.4x10^-13 to 1.6x0^-10, is the lowest reported for
any eukaryote. These results are consistent with low microsatellite mutation
rates previously observed in D. discoideum and low levels of genetic
variation observed in wild D. discoideum populations. In addition,
D. discoideum has been shown to be quite resistant to DNA damage, which
suggests an efficient DNA-repair mechanism that could be an adaptation to
life in soil and frequent exposure to intracellular and extracellular mutagenic
compounds. The social aspect of the life cycle of D. discoideum and a
large portion of the genome under relaxed selection during vegetative
growth could also select for a low mutation rate. This hypothesis is
supported by a significantly lower mutation rate per cell division in
multicellular eukaryotes compared with unicellular eukaryotes.
Submitted by Gerda Saxer [[log in to unmask]]
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[End dictyNews, volume 38, number 24]
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