Interesting abstract by Gerda from David's group!
How do you fit into these findings the relavively rapid loss of 
developmental competence in cultures that grow for some time in ax. 
medium?
We assume (but have no experimental proof yet)that epigenetic 
mechanisms may play a substantial role in variability. Does anyone 
have data along these lines? It may be worth to take this into 
consideration.
wolfgang


> 
> 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]]
> ==============================================================
> [End dictyNews, volume 38, number 24]

Wolfgang Nellen
Abt. Genetik
Univ. Kassel
Heinrich-Plett-Str. 40
34132 Kassel
Germany