The rate and spectrum of microsatellite mutation in Caenorhabditis elegans and Daphnia pulex - PubMed (original) (raw)

The rate and spectrum of microsatellite mutation in Caenorhabditis elegans and Daphnia pulex

Amanda L Seyfert et al. Genetics. 2008 Apr.

Abstract

The effective use of microsatellite loci as tools for microevolutionary analysis requires knowledge of the factors influencing the rate and pattern of mutation, much of which is derived from indirect inference from population samples. Interspecific variation in microsatellite stability also provides a glimpse into aspects of phylogenetic constancy of mutational processes. Using long-term series of mutation-accumulation lines, we have obtained direct estimates of the spectrum of microsatellite mutations in two model systems: the nematode Caenorhabditis elegans and the microcrustacean Daphnia pulex. Although the scaling of the mutation rate with the number of tandem repeats is highly consistent across distantly related species, including yeast and human, the per-cell-division mutation rate appears to be elevated in multicellular species. Contrary to the expectations under the stepwise mutation model, most microsatellite mutations in C. elegans and D. pulex involve changes of multiple repeat units, with expansions being much more common than contractions.

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Figures

F<sc>igure</sc> 1.—

Figure 1.—

Scaling of the mutation rate with the number of repeat units in the ancestral locus on a per-cell-division basis. The data for C. elegans are taken directly from this study, with the data for the two shortest length classes being pooled, as most such loci exhibited no mutations. We assumed 10 germline cell divisions per generation for this species. The data for yeast are taken from direct observations on dinucleotide repeats from W

ierdl

et al. (1997) and L

egendre

et al. (2007). The data for Dictyostelium are taken from M

c

C

onnell

et al. (2007). The data for humans are pooled from several parent–offspring analyses (□) (B

rinkmann

et al. 1998; L

eopoldino

and P

ena

2003; H

enke

and H

enke

2006; H

ohoff

et al. 2007) and assume 200 germline cell divisions per generation. The mammalian cell-line data (▵) are taken from experimental investigations by Y

amada

et al. (2002) and H

ile

et al. (2000) of mice and humans, respectively. Due to the lack of germline developmental data, we cannot include D. pulex in this comparison. The data for C. elegans and S. cerevisiae are fitted with second-order polynomials, respectively: y = −10.70 + 4.56_x_ − 0.44_x_2 (r_2 = 0.962) and y = −11.78 + 5.08_x − 0.53_x_2 (r_2 = 0.874). The mammalian data are fitted to the combined linear regression y = −8.09 + 2.77_x (_r_2 = 0.749).

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