Interesting Ibiology lectures on development.
Eric Wieschaus (Princeton) Part 1: Patterning Development in the Embryo
Below you can find some pictures and movies of the microtubule cytoskeleton.
The microtubule (MT) network plays an essential role in dividing cells, as during mitosis, MTs form the cables that segregate the genetic material(DNA) and divide it equally over the two daughter cells. In the movie below you see the MT network during the first three stages of mitosis. It starts with prophase. During this phase of mitosis, the centrosomes, or MT organizing centers, move to opposite sides of the nucleus. The centrosomes are localized in the center of the two bright spots. The nuclear envelope is still intact as the nucleus (the black circle between the two bright spots), is very dark compared to the cytoplasm. During prometaphase (after a few frames), the intensity of the nucleus starts to increase. This is an indication that the nuclear envelope is breaking down, and cytoplasmic proteins diffuse into the nucleus. In this case the fluorescence that we observe is freely diffusing mCherry-tubulin (which has not yet been incorporated into a MT). You can even recognize the chromosomes, because of the contrast. They are the darker "sausages" in between the two bright spots. In other places of the cytoplasm you can also recognize some small dark spots, those are organelles, such as mitochondria and endosomes. During this phase of mitosis, the cell also starts to round up. MTs growing from the centrosomes now begin to capture the chromosomes, and start lining them up. Because the cell rounds up i had to adjust the focus. During metaphase, the cell has lined up all the chromosomes. MTs from both poles (centrosomes) are pulling on each chromosome and are really exerting force on it. This pulling is like tug-of-war, with both poles being equally strong. This helps to line up each chromosome exactly in the center of the mitotic spindle. Now the cell is ready to go into the next phase of mitosis called anaphase, where the MTs start pulling the sister chromatids to opposite sides of the cell. I will try to make a nice movie of this part of mitosis and upload it here soon. If you have any questions or comments, send me an email. You can find my email address below.