Variability and heritability of cell division pathways in Toxoplasma gondii.

A histone 2b-YFP fusion protein stably expressed in Toxoplasma gondii has several advantages: it reveals previously hidden details of nuclear morphology; it makes it possible to observe cell-cycle events; it provides a basis for quantitative measurements of DNA content in living cells; and it enables sorting of live cells according to cell-cycle phase or ploidy. With this cell line it was possible to recognize and directly clone individual progeny arising from different patterns of cell division that produce two, three or four daughter cells. These experiments established that the progeny produced by all cell division pathways are viable and infective. Furthermore, the number of progeny produced by a mature parasite during cell division is not correlated with the number of its siblings. The complete repertoire of cell division pathways is therefore inherited by a single cell produced through any one of the individual paths. The results expand the range of what must be considered normal in T. gondii cell division and provide a useful tool for further study of nuclear structure and proliferation in this important human pathogen.