Figure 1.

Examples of microtubule organization in animal cells (depictions are simplified; see main text for details). The centrosome is the dominant microtubule-organizing center (MTOC) in proliferating cells (green panel). Differentiated cell types like neurons or striated muscle cells exhibit various non-centrosomal MTOCs and attenuate/inactivate or, as described for cardiomyocytes, disassemble their centrosomes (blue panel). Certain types of epithelial cells are “intermediates”, i.e., they retain microtubule nucleation ability at centrosomes but anchor microtubules mainly at non-centrosomal sites (cyan panel). In addition, several alternative microtubule-organizing pathways (grey panel) are active in proliferating as well as differentiated cells (neurons in particular) that act in synergy with the dominant MTOC.