When starved, Dictyostelium amoebae differentiate into either spores or stalk cells. This decision partly depends on the cell-cycle status of a cell at the time of starvation. MacWilliams and co-workers now report that rblA, the Dictyostelium orthologue of the retinoblastoma susceptibility gene Rb, controls stalk/spore preference (see p. 1287). They show that,during growth, rblA expression correlates with factors that favour spore formation (late cell-cycle position, good nutrition) and that it increases 200-fold in differentiating spores. rblA-null strains show a strong preference for stalk formation when mixed with wild-type cells and are hypersensitive to the stalk morphogen DIF in vitro, indicating that rblA suppresses the DIF response in cells destined to be spores. However, rblA is not important for the Dictyostelium cell cycle. As Rb is required for both differentiation and cell-cycle exit in plants and animals, the researchers propose that Dictyostelium has retained the differentiation-Rb link but has lost the Rb-cell-cycle exit link to avoid shunting starving cells into the spore pathway.

© 2006.
2006