Divergence of mitotic strategies in fission yeasts.

The aim of mitosis is to produce two daughter nuclei, each containing a chromosome complement identical to that of the mother nucleus. This can be accomplished through a variety of strategies, with "open" and "closed" modes of mitosis positioned at the opposite ends of the spectrum and a range of intermediate patterns in between. In the "closed" mitosis, the nuclear envelope remains intact throughout the nuclear division. In the "open" division type, the envelope of the original nucleus breaks down early in mitosis and reassembles around the segregated daughter genomes. In any case, the nuclear membrane has to remodel to accommodate the mitotic spindle assembly, chromosome segregation and formation of the daughter nuclei. We have recently shown that within the fission yeast clade, the mitotic control of the nuclear surface area may determine the choice between the nuclear envelope breakdown and a fully "closed" division. Here we discuss our data and argue that comparative cell biology studies using two fission yeast species, Schizosaccharomyces pombe and Schizosaccharomyces japonicus, could provide unprecedented insights into physiology and evolution of mitosis.