Cytoplasmic streaming - in which RNA and protein is transported from polyploid nurse cells to the growing oocyte - in Drosophila is well documented; however, little is known about how cytoplasmic materials accumulate in growing C. elegans oocytes, which lack nurse cells. James Priess's lab now reveals that mitochondria and germline-specific proteins - in addition to injected foreign material, such as oil droplets or polystyrene beads - travel from the gonad region, where pachytene nuclei are situated, to the oocyte, supporting the view that pachytene-stage nuclei function as transient nurse cells before differentiating into oocytes (see ). Interestingly, and in contrast to Drosophila where cytoplasmic materials are pushed into the oocyte from nurse cells, in the worm cytoplasmic material is pulled into the enlarging oocyte by acto- and myosin-dependent forces generated adjacent to, or even within, the enlarging oocyte. RNAi-knockdown studies reveal that microtubules are not essential in this streaming event. Future studies are likely to focus on the molecular mechanisms that regulate this key process.
