Current Biology
Volume 25, Issue 6, 16 March 2015, Pages 732-740
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Article
Scaling, Selection, and Evolutionary Dynamics of the Mitotic Spindle

https://doi.org/10.1016/j.cub.2014.12.060Get rights and content
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Highlights

  • Spindles exhibit extensive variations between individuals of the same species

  • Variations in spindles are correlated with variations in cell size

  • In nematodes, embryo size, and thus cell size, is subject to stabilizing selection

  • Selection on cell size explains within- and between-species variations in spindles

Summary

Background

Cellular structures such as the nucleus, Golgi, centrioles, and spindle show remarkable diversity between species, but the mechanisms that produce these variations in cell biology are not known.

Results

Here we investigate the mechanisms that contribute to variations in morphology and dynamics of the mitotic spindle, which orchestrates chromosome segregation in all Eukaryotes and positions the division plane in many organisms. We use high-throughput imaging of the first division in nematodes to demonstrate that the measured effects of spontaneous mutations, combined with stabilizing selection on cell size, are sufficient to quantitatively explain both the levels of within-species variation in the spindle and its diversity over ∼100 million years of evolution. Furthermore, our finding of extensive within-species variation for the spindle demonstrates that there is not just one “wild-type” form, rather that cellular structures can exhibit a surprisingly broad diversity of naturally occurring behaviors.

Conclusions

Our results argue that natural selection acts predominantly on cell size and indirectly influences the spindle through the scaling of the spindle with cell size. Previous studies have shown that the spindle also scales with cell size during early development. Thus, the scaling of the spindle with cell size controls its variation over both ontogeny and phylogeny.

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