Quantifying the range of a lipid phosphate signal in vivo.

Quantitative information about the range of influence of extracellular signaling molecules is critical for understanding their effects, but is difficult to determine in the complex and dynamic three-dimensional environment of a living embryo. Drosophila germ cells migrate during embryogenesis and use spatial information provided by expression of lipid phosphate phosphatases called Wunens to reach the somatic gonad. However, whether guidance requires cell contact or involves a diffusible signal is not known. We ectopically expressed Wunens in various segmentally repeated ectodermal and parasegmental patterns in embryos otherwise null for Wunens and used germ cell behavior to show that the signal is diffusible and to define its range. We correlated this back to the wild-type scenario and found that the germ cell migratory path can be primarily accounted for by Wunen expression. This approach provides the first quantitative information of the effective range of a lipid phosphate in vivo and has implications for the migration of other cell types that respond to lipid phosphates.