Volume 6 Issue 12, December 2004

The finding that Eps8 caps the barbed ends of actin filaments adds to the growing list of factors responsible for controlling the dynamics of actin polymerization. The requirements for these capping proteins may vary in each cellular context, but EPS-8 seems to be critical during intestinal morphogenesis in the worm.

How do cells track down the occasional lesion among the billons of base pairs of chromosomal DNA? A surprising discovery unravels a potential new mechanism: the Tudor domains of the DNA-damage response factor 53BP1 interact with methylated histones that are likely to become exposed during local chromatin relaxation at sites of DNA double-strand breaks.

The cell cycle regulator p27^Kip1 must be degraded to permit cell division. Degradation is moderate in G1 phase, but is enhanced in S-phase. Now, a novel ubiquitin ligase that can ubiquitinate p27 leading to its proteolysis after mitogen stimulation has been identified.

Growing evidence suggests that semaphorins — known to provide directional cues during axon guidance — also provide regulatory signals for cell migration during tissue morphogenesis. During heart development, it is crucial that semaphorins can signal bidirectionally, functioning as both a ligand and a receptor. Through these distinct signalling pathways, semaphorins can provide both 'stop' and 'go' signals for cell motility and invasive growth.

Formins are a family of structurally conserved proteins that regulate the assembly of the fast-growing end of actin filaments. New work shows that the molecular mechanism of formin function is conserved but that the rates of the reactions vary within and between species to such a degree that the mechanisms of various formin family members may seem to differ qualitatively.