Wg was thought to promote cell proliferation because loss of Wg signaling leads to a small wing structure. But Johnston now shows that small wings arise because Wg is required for cell survival in the early stages of wing development, when cells are rapidly proliferating. In these surviving cells, however, Wg actually slows cell growth and division. When the authors removed Wg but prevented cell death, the cells proliferated faster than usual. Conversely, overexpression of Wg slowed proliferation.
Wg's negative effects on cell proliferation were seen mostly in late stages of development, suggesting that perhaps cells must first achieve some level of differentiation before Wg can arrest growth. Thus, Wg may signal that the organ has had sufficient time to differentiate and is now ready to halt growth. ▪