Activating actin

On page 677, Hudson and Cooley characterize Drosophila melanogaster strains with defects in the evolutionarily conserved actin nucleation factor Arp2/3. The work provides significant new insights into the specificity of Arp2/3 activity.During Drosophila egg development, intercellular connections called ring canals form between nurse cells and developing oocytes, allowing cytoplasm from the nurse cells to flow into the oocytes. These processes require at least three distinct types of actin structures: contractile actin to squeeze cytoplasmic contents, actin to keep ring canals open, and bundles of actin filaments that position the nucleus and stop it from clogging the ring canals. Similar actin bundles are also seen during metamorphosis, when the growth of bristles on the pupal epithelium requires hexagonally packed bundles of actin filaments.

In the new work, Hudson and Cooley found that flies...