Though division timing was unaffected, TD cells did transiently alter their cell cycle phasing; they passed quickly through G1 and lagged in S phase. This phase change preceded TD. A longer S phase might allow time for chromatin changes that are needed for the different cell fate, and the authors propose that Wg induces chromatin remodeling proteins such as Polycomb.
Cells with the unusually long S phase were also larger than non-TD cells. Bursts of biosynthetic activity may be the driving force for the phase changes and subsequent developmental plasticity, but this remains to be shown. Forcing growth and division by overexpressing insulin pathways induced some fate changes but did not induce TD to wing. Wg may also have morphogenic properties. “We can speculate,” says Schubiger, “that Wg targets TD cells and acts as a mitogen. But we believe that only sustained Wg signaling causes a change [in cell fate].