The dramatic cell movements that occur during gastrulation are influenced by extracellular signals. Because the highly conserved WAVE complex - which regulates the actin cytoskeleton - couples extracellular signals to cell migration, Rakeman and Anderson investigated the role of the WAVE complex in early vertebrate development (see ). They identified mice lacking Nap1 - a regulatory component of the complex - and found that without Nap1 the WAVE complex in embryos is unstable. Moreover∼25% of Nap1 mutants had a duplicated anteroposterior axis (other embryonic defects included the slowed migration of endoderm and mesoderm). This axis is determined by the position of the primitive streak, which is itself determined by anterior visceral endoderm (AVE) movement. The authors suggest that Nap1 is required for the normal polarisation and active migration of AVE cells, and conclude that, during mammalian development, the WAVE complex is vital for the regulation of actin during tissue organisation and the establishment of the body's main axes.
