FIGURE 18-29 Movement of pigment granules in frog melanophores. (a) Diagram of the microtubule-based reorganization of melanosomes according to the level of cAMP. Melanosomes are aggregated by cytoplasmic dynein and dispersed by kinesin-2. (b) Melanosomes (red) in the dispersed state as seen by immunofluorescence microscopy. Microtubules are labeled green, and the DNA in the nucleus is labeled blue.

[Part (b) courtesy of Steve Rogers.]