In oocytes, DCAP-2 (red) resided in granules that were distinct (arrows and arrowheads) but often adjacent (arrowheads) to CGH-1 granules (grP bodies) (green).
Boag et al. showed that P bodies in eggs lack an mRNA decapping protein called Pat1 that in somatic cells promotes mRNA degradation. So if egg P bodies aren't degrading mRNA, what are they doing? A core P body component called CGH-1 holds mRNAs at P-bodies in both somatic cells and egg cells. When the authors removed CGH-1 from eggs, mRNAs were mislocalized and destabilized. “We think CGH-1 acts like a chaperone for a protective mRNA-protein complex,” says PI Keith Blackwell. The oocyte contains large numbers of maternally derived mRNAs, which are all transcribed and packaged at once, but then used in a specific temporal pattern for proper development. The protective complex may keep them safe until they are expressed.
Noble et al. showed that eggs in fact have a whole range of specialized P bodies. They identified at least three types of P bodies arising at different stages of egg development, and a fourth type in embryos, each with a distinct set of proteins. During early meiosis, “germ granules” associate with germ nuclei, while grP (germline RNP) bodies accumulate in the syncytial (multinucleate) cytoplasm. Neither type carried the RNA decapping enzyme DCAP-2, suggesting they do not degrade mRNA, in line with the observations of Boag et al. As mononucleate oocytes formed and then entered an arrested stage, dcP bodies appeared, which did contain DCAP-2, but, interestingly, didn't contain measurable amounts of CGH-1. Finally, during early embryogenesis, more canonical P bodies form, carrying CGH-1 and decapping enzymes.
Although the different types of P bodies most likely have different functions, they do appear to interact with one another, indicating that they exchange mRNAs. Thus, sorting out which P bodies do what will be a challenging next step.
