Seminars

Asymmetric divisions produce daughter cells with different fates, which is important for development in many organisms. For a division to be asymmetric, the cell must become polarized, with an unequal distribution of fate-determining molecules. The cell must also divide on a plane that segregates more of those molecules to one daughter cell. In animal cells, the division plane orientation is determined by the position of the mitotic spindle. In the C. elegans one-cell embryo, as in many systems, the PAR proteins establish polarity and a conserved cortical complex recruits the microtubule motor dynein to provide forces that can move the spindle. I will discuss our work showing that the DEP domain protein LET-99 is a key intermediate that inhibits the cortical complex to generate unequal pulling forces to orient the spindle on the polarity axis. We have also shown LET-99 is a regulator of a later asymmetric division that depends on cell signaling rather than PAR polarity. During both divisions, LET-99 may act by down-regulating G proteins.