Animal cells have something called a centrosome, also called a microtubule organizing center, or MTOC. The surface of the MTOC is studded with microtubule nucleation complexes from which microtubules arise and to which they remain tethered. Given these constraints, its not hard to see why microtubules form starburst arrays around centrosomes.
But there are many cell types that have ordered microtubule arrays that aren't created by centrosomes. Some nerve cells, for example, have very long projections (axons) that are chock full of microtubules.
The microtubules are aligned with the axis of the axon and they're not connected to the cell's centrosome in the cell body, which can be some distance away. "How do you order microtubules and generate a specific pattern when you don't have centralized control?" asks Dixt, an assistant professor of biology in Arts & Sciences.
The same question arises with muscle cells, which also have linear microtubule arrays and with the cells that line the gut, which have flat microtubule arrays in their flanks. In both cases, the arrays are distant from the cell's microtubule organizing center.
The cytoskeletons in the cells of land plants are also patterned according to function without the help of a centrosome.
The guard cells that open and close the stomata on the under surface of plant leaves, for instance, have fan-shaped arrays that follow their curves. Pavement cells on the leaf surface that are shaped like interlocking puzzle pieces have net-like arrays. And rapidly elongating cells in plant stems have transverse arrays that then reorient toward the longitudinal direction as growth slows.
Lit up like a Christmas tree
It's hard to study these arrays in animal cells, says Dixit. "The microtubules go deep into the cytosol and are hard to manipulate or image at high resolution. Be
|Contact: Diana Lutz|
Washington University in St. Louis