I.C. Alternative model: Two stages of pattern formation

We have reason to believe that the process of pattern formation occurs in two stages (see figure):

1. Production of initial crude pattern
2. Resolution of contiguous differentiating cells into a single heterocyst

The first stage appears to occur in only a fraction of cells in a filament. We are examining the possibility that a cell's position in the cell cycle determines whether it will be competent to enter the first stage.

To test this possibility, we have asked:

• Is there a correlation between a cell's position in the cell cycle and the pattern of heterocyst differentiation?
• Does perturbing the cell cycle also perturb the pattern of heterocyst differentiation?

The cell cycle plays an increasingly recognized role in eukaryotic differentiation. Understanding the precise way it enters into the decision-making process in the simple case of Anabaena may provide insights into more complicated instances.