Have I told you how incredibly and absurdly obsessed I am with the cell cycle? I oscillated for a long time between thinking that the cell cycle is a trivial aspect of differentiation and growth, and thinking that it is impossible to understand animal biology without the cell cycle. Increasingly, I am convinced that a profound understanding of the cell cycle is lacking, and what we call “the cell cycle” is actually a set of cellular programs that look similar but do different things.

This perspective was further sharpened at last week’s SCDB conference in a talk by Semil Choksi, who presented a talk on an alternative cell division program that leads to maturation of ciliated cells. Semil drew a slide that inspired me because he captured the thinking far more clearly than I have ever managed to capture it before. In his slide, Semil showed the different cell cycle programs as we know them: The standard cell cycle, which duplicates all machinery, the meiotic cycle which quadruplicates and randomizes all machinery, the endoreduplication cycle which duplicates the nuclear contents, and he added his contribution, a program that multiplies centrioles (and in my opinion can be seen as a program to duplicate the cytoplasmic machinery). How many more cycle programs are missing, I wonder?

I have this recurring dream that the cell cycle program is a standard duplication program, and that by turning on or off certain addenda programs, the cell cycle can be tuned to duplicate specific cellular components in a separable manner. In turn, this makes me wonder whether a complete understanding of the cell cycle could help us understand how to refunctionalize cells without the risk of cancer. After all, even partial reprogramming by OSKM looks very much like direct stimulation of the cell cycle.