Heads or tails: cell polarity and axis formation in the early Caenorhabditis elegans embryo.

In C. elegans, the first embryonic axis is established shortly after fertilization and requires both the microtubule and microfilament cytoskeleton. Cues from sperm-donated centrosomes result in a cascade of events that polarize the distribution of widely conserved PAR proteins at the cell cortex. The PAR proteins in turn polarize the cytoplasm and position mitotic spindles. Lessons learned from C. elegans should improve our understanding of how cells become polarized and divide asymmetrically during development.