To see what happens in the cells, the team put the culture dishes under a microscope that took pictures automatically once a minute. Then they removed EGF from the cells' culture and let them settle in and quiet down. The cells looked like fried eggs awash in light green.
When the team returned EGF to the culture dishes, the nucleus within cells -- what looks like an egg yolk -- brightened up with green, indicating the ERK proteins were flooding into the nucleus. After a few minutes, the green drained from the nucleus back into the cell proper, only to return again after some time. The oscillations in individual cells cycled about every 15 minutes, starting out in sync but losing that coordination over time.
Also, the time-lapse video showed that cell reproduction didn't seem to affect the cycling. The oscillations continued regularly throughout cell growth. Then the oscillations briefly stopped while one cell divided into two daughter cells. As cell division finished up, the oscillations resumed.
Additional experiments showed the oscillations required EGF in the cell culture and continued for up to ten hours, the longest period of time the researchers observed. In addition, the number of cells with oscillating ERK depended on how crowded the living conditions were. For example, the team found that at the lowest numbers of cells, all of them showed oscillating ERK. As the cells reproduced, fewer cells oscillated. By the time the cells filled the whole surface of their dish, virtually all of the cells lost their cycling ERK.
A Model ERK
One way scientists determine how well they understand the workings of a cell is to see if they can simulate it in a computer program. Wiley and his colleagues developed such a model that included the oscillating ERK, as well as most of the players in the chain of command from EGF receptor on.
To test the model, the team first us
|Contact: Mary Beckman|
DOE/Pacific Northwest National Laboratory