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First published online September 26, 2003
doi: 10.1242/10.1242/jcs.00816

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Animal cell division: a fellowship of the double ring?

Robert Saint and W. Gregory Somers^*

Centre for the Molecular Genetics of Development, Research School of Biological Sciences, Australian National University, Canberra ACT 0200, Australia

View larger version (97K): [in a new window]   Fig. 1. Formation of a partial contractile ring during the first meiotic division of a D. melanogaster spermatocyte carrying a mutation in the chickadee (profilin) gene. A wild-type spermatocyte is shown in A and the chickadee mutant spermatocyte shown in B. Microtubules are stained green, DNA blue and F-actin red. Reproduced, with permission, from Giansanti et al. (Giansanti et al., 1998).

View larger version (34K): [in a new window]   Fig. 2. Manipulation of sea urchin embryos to generate ectopic astral spindles in the absence of chromosomes revealed the significance of microtubules, rather than chromosomes, in positioning the contractile apparatus. The blue ring represents a solid cylinder pushed through the center of an embryo to create a torus. The first mitotic division induces furrowing at the spindle midzone, but no cleavages are observed at positions distant from the spindle. The second mitotic divisions induce furrowing at the two spindle midzones, but, in addition, furrowing appears between the two spindle poles in the absence of metaphase chromosomes or anaphase movements. Adapted, with permission, from Rappaport (Rappaport, 1971).

View larger version (48K): [in a new window]   Fig. 3. The double ring model of cytokinesis positioning. Centralspindlin complexes move to the midzone along microtubules where they concentrate and activate the RhoGEF through a direct protein-protein interaction. This leads to a cortical ring of activated Rho1 between the separated chromosomes. The activated Rho1 leads to formation and activation of the actomyosin contractile ring (not shown).

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