Controlling division planes

In mammals, cells that divide with their spindle axis parallel to the surface of the epithelial sheet produce symmetric daughters, whereas a spindle perpendicular to the sheet produces asymmetric progeny. Poggi et al. (page 991) report that environmental factors can affect spindle orientation in the zebrafish retina and thus alter cell fate.

Retinal ganglion cell (RGC) formation is dependent on Ath5. Using time-lapse microscopy, the team found that as cells began to express Ath5 they migrated toward the outer surface of the cup-shaped retina. Once there, the cells divided one time, with the plane of their spindle oriented along the radial axis of the retina (i.e., perpendicular to the sheet). One daughter cell migrated back toward the center of the retina and became an RGC, while the other remained near...