Rosettes for elongation

A blob becomes a body by becoming thinner and longer—a process that involves cell shuffling called intercalation. Flies do it by making and resolving rosettes of cells, say J. Todd Blankenship, Jennifer Zallen, and colleagues (Sloan-Kettering Institute, New York, NY). Up to 11 cells join these pinwheels, which squeeze together cells that were arrayed in the dorsal–ventral axis, before letting them relax back into a line running from anterior to posterior.

The rosettes are striking, but it has taken a long time for them to be identified. “I also spent a lot of time not seeing them,” says Zallen. “It was making movies that made the difference—then you see they are directional. Now when I read papers I see them all the time.”

In a previous model for elongation, called neighbor...