Cell polarity in one-cell C. Elegans Embryos: Ensuring an accurate and precise spatial axis during development

Cell polarity in one-cell C. elegans embryos guides an asymmetric cell division that starts the resulting cells along different developmental paths. Cell polarization starts in response to a signal from the centrosomes, triggering a cellwide reorganization of the cortex. Functionally, the most notable change is the establishment of two mutually exclusive, antagonistic cortical domains, each composed of distinct PAR proteins. PAR proteins are a diverse but generally conserved group of polarity regulators that exert their polarizing effects through different downstream components. In one-cell C. elegans embryos, PAR polarity dictates the asymmetric segregation of fate determinants in the cytoplasm and controls the position of the cleavage furrow, allowing for unequal cell division. C. elegans embryos have been informative in identifying cell polarity factors, largely because embryo development is invariant and thus deviations from normal are easy to detect. It is becoming increasingly apparent that the invariance of C. elegans polarization results from parallel pathways and backup mechanisms that ensure robustness when components vary or the system is compromised. Recent work now points to a significant role of protein homeostasis in the accuracy and precision of polarity establishment in C. elegans, raising questions about the regulatory circuits that underlie this robustness.