Current efforts in diverse model systems continue to refine, frequently with quantitative precision, key parameters governing “typical” cell cycle progression. However, instead of typical cell cycle programs, numerous developing or regenerating tissues employ cell cycle variations. One commonly used variation, frequently referred to as an endocycle, eliminates or prematurely ends the division phase (mitosis). Endocycles lead to multiple genome duplications, a cellular property known as polyploidy. The mammalian heart, liver, placenta, and blood all contain polyploid cells, and polyploidy also occurs in an estimated 37% of all human cancers. However, compared to "typical" cell cycles, we know comparably little about the regulation and biological purposes of endocycles or polyploidy.
We found that papillar cells of the Drosophila hindgut require division of endocycled (polyploid) cells for physiologically important organ construction. By examining our newly identified uses for endocycles/polyploid division, we are beginning to understand why some organs cannot be built (or potentially function) using only "typical" cell cycles. Additionally, we have found that a property of endocycles considered incompatible with normal mitosis-- altered chromosome structure-- is completely reversible. Thus, our work promises to extend conventional thinking about the regulation and use of endocycles/polyploidy.