Oscillation sensation

摘要

Various molecular actors play out the scene in which a cell exits mitosis―nuclear division―before entering the next cell cycle. One of them, the protein Clb2, steps back into the spotlight. Another, Clb5, bows out. In 1982, while studying events in the early sea-urchin embryo, Tim Hunt found that one particular protein―which he called cyclin―is made and destroyed in each cell cycle. Murray and Kirschner later discovered that, in frog embryos, cyclins are the only proteins that need to be newly synthesized for the cell cycle to occur. Frog eggs are giant storehouses of many proteins necessary for cell division. So why couldn't cyclins be stockpiled like the others? The answer came from a key experiment by the same investigators: it showed that cyclin degradation can be prevented by removing a 'destruction box' sequence on the protein, and with dramatic results. When cyclin turnover was prevented, the cell cycle was blocked in mitosis. In other words, the alternating synthesis and degradation of cyclin is necessary for entry into and exit from mitosis. Here was a first glimpse of the molecular oscillator that underlies the cyclical nature of cell division. On page 556 of this issue, Waesch and Cross bring our understanding of this oscillator closer to maturity.