Wandering fly eggs shed light on migration
In a search for a technique that allowed real-time observation of border cell migration, the researchers found that the addition of insulin to typical insect growth medium allowed the egg chambers to be cultured for long enough to observe migration. The border cells were labeled with fluorescent protein so they could be tracked as they migrated.
The border cells take four to six hours to migrate from one end of the egg chamber to the oocyte at the other end, moving at an average speed of 0.54 micrometers per minute. At this rate, it would take over two hours to cross the width of a human hair. Before border cells move, they extend protrusions, or extensions of the plasma membrane, which they use to pull themselves along in much the same way as a snail's false foot.
The researchers were able to track the movements of one cell relative to the others. They found that a cell started and ended migration in the front of the cluster, but moved to positions at the side and rear of the cluster while migrating. The reasons for this pattern are unclear.
The researchers also examined border cell mutants, which are unable to migrate normally because they do not express two specific cell surface receptors, called PVR and EGFR. These receptors allow the oocyte to instruct the border cells to move by binding to the oocyte's chemical signals.
Previously scientists believed that border cells without PVR and EGFR did not extend any protrusions, which is why they would not be able to move. However, real-time observation of cell migration demonstrated that the border cell cluster sent out protrusions in all directions. Effectively the cells could not "choose" which direction to move, so they stayed in place.
The researchers concluded that normal cells send out protrusions in the direction of the growth hormone and move accordingly.
The border cells take four to six hours to migrate from one end of the egg chamber to the oocyte at the other end, moving at an average speed of 0.54 micrometers per minute. At this rate, it would take over two hours to cross the width of a human hair. Before border cells move, they extend protrusions, or extensions of the plasma membrane, which they use to pull themselves along in much the same way as a snail's false foot.
The researchers were able to track the movements of one cell relative to the others. They found that a cell started and ended migration in the front of the cluster, but moved to positions at the side and rear of the cluster while migrating. The reasons for this pattern are unclear.
The researchers also examined border cell mutants, which are unable to migrate normally because they do not express two specific cell surface receptors, called PVR and EGFR. These receptors allow the oocyte to instruct the border cells to move by binding to the oocyte's chemical signals.
Previously scientists believed that border cells without PVR and EGFR did not extend any protrusions, which is why they would not be able to move. However, real-time observation of cell migration demonstrated that the border cell cluster sent out protrusions in all directions. Effectively the cells could not "choose" which direction to move, so they stayed in place.
The researchers concluded that normal cells send out protrusions in the direction of the growth hormone and move accordingly.
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