Schematic representation of the localizations of proteins that regulate spindle positioning in the single-cell embryo. (A) Localization of PAR proteins, LET-99, and GPR-1/2 in wild-type embryos based on previous work (Gotta and Ahringer, 2001; Colombo et al., 2003; Bringmann et al., 2007; Wu and Rose, 2007; Panbianco et al., 2008; Park and Rose, 2008). In this, and all subsequent figures, 0% embryo length marks the anterior pole, and embryos are oriented with the anterior to the left. (B) Three force domain model for anaphase spindle positioning in wild-type embryos. The thickness of the arrows indicates proposed magnitude of force acting on microtubules from the corresponding cortical region.