Figure 1.

P granule formation in the C. elegans one-cell embryo. Formation of this organelle is proposed to occur through a dissolution/aggregation mechanism. After fertilization, P granule components (both RNAs and proteins) are distributed uniformly throughout the cytoplasm. Upon specification of the anterior–posterior axis, the posterior polarity protein PAR-1 (blue) promotes their aggregation. As a consequence, P granules assemble specifically in the posterior of the embryo. Once aggregated, P granule components diffuse more slowly and therefore remain preferentially in the posterior compartment of the embryo. On the anterior of the embryo, MEX-5 (red) promotes the dissolution of P granules. Once the different components are in solution in the anterior, they diffuse more rapidly and can replenish the posterior pool. Cleavage results in the inheritance of P granules only in the posterior daughter cell (the P1 cell).