How to terminate a shmoo

Many types of cells grow polarized structures of defined sizes, but virtually nothing is known about how a cell starts and stops this process. On page 207, Bidlingmaier and Snyder provide the first report of regulatory proteins involved in this timing control, and find that initiation and termination of polarized growth are controlled by distinct but overlapping sets of proteins.

The authors investigated the growth of mating projections in Saccharomyces cerevisiae. This yeast responds to gradients of pheromone by assuming a shmoo-like shape pointing in the direction of the signal. Shmoos still form in the presence of uniformly high concentrations of pheromone (as may result when cells are closely packed together), but they poke out sequentially in random directions to sample the environment. Bidlingmaier and Snyder found that the time between...