This Fourth of July, many of you will spread out a blanket and enjoy an evening display of fireworks with their dramatic, colorful bursts. But here’s one pyrotechnic pattern that you’ve probably never seen. In this real-time video, researchers set off some fluorescent fireworks under their microscope lens while making an important basic discovery about how microtubules, the hollow filaments that act as the supportive skeleton of the cell, dynamically assemble during cell division.
The video starts with a few individual microtubule filaments (red) growing linearly at one end (green). Notice the green “comets” that quickly appear, followed by a red trail. Those are new microtubules branching off. This continuous branching is interesting because microtubules were generally thought to grow linearly in animal cells (although branching had been observed a few years earlier in fission yeast and plant cells). The researchers, led by Sabine Petry, now at Princeton University, Princeton, NJ, showed for the first time that not only do new microtubules branch during cell division, but they do so very rapidly, going from a few branches to hundreds in a matter of minutes .
Petry and her colleagues initially wanted to know how dividing cells assemble their mitotic spindles, the specialized structures made primarily of stacked microtubules that tether the chromosomes as one cell splits into two. But they had a problem: despite the tremendous progress in cell imaging, it was still not possible to tell microtubules apart from each other inside a dividing cell. It’s simply too crowded in there to make out exactly when and how the spindles are assembled.
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