Microtubule organising centres (MTOC)

Microtubules are nucleated throughout the cytoplasm, but are especially concentrated around the nucleus. When colcemid is added to cells injected with fluorescent tubulin, microtubules disassemble. When colcemid is removed microtubules can be seen to grow from this microtubule organising centre (MTOC). In animal cells this is the centrosome. In this manner the minus ends of microtubules are at the MTOC near the nucleus and the plus ends at the cell periphery.