olarizing cells must first pick a direction. The external cues that guide this choice are obvious: bud scars or mating partners for budding yeast, and chemoattractant gradients for Dictyostelium and neutrophils. But polarization still occurs, albeit in a random direction, when these cues are either removed or made uniform. Now, Roland Wedlich-Soldner, Rong Li (Harvard Medical School, Boston, MA...

The adult epidermis in higher dipteran insects such as Drosophila is derived from specialized structures in larvae known as imaginal discs. Set aside during mid-embryogenesis as small groups of 10 to 70 cells each, imaginal disc primordia grow and differentiate during larval development as epithelial monolayers. Metamorphosis of imaginal discs during early pupal life generates the adult cuticle...

The surface distribution of concanavalin A (Con A) bound to cell membrane receptors varies dramatically as a function of mitotic phase. The lectin is distributed diffusely on cells labeled and observed between mid-prophase and early anaphase, whereas cells observed in late anaphase or telophase demonstrate a marked accumulation of Con A-receptor complexes over the developing cleavage furrow (Be...

We investigate the final stage of cytokinesis in two types of amoeba, pointing out the existence of biphasic furrow contraction. The first phase is characterized by a constant contraction rate, is better studied, and seems universal to a large extent. The second phase is more diverse. In Dictyostelium discoideum the transition involves a change in the rate of contraction, and occurs when the wi...

Animal cells are deformable, yet live together bound into tissues. Consequently, physical perturbations imposed by neighbors threaten to disrupt the spatial coordination of cell cleavage with chromosome segregation during mitosis. Emerging evidence demonstrates that animal cells integrate multiple positional cues during cleavage-furrow induction, perhaps to facilitate error correction. Classica...