COMMENTARY Mechanisms of nuclear positioning

The mechanisms underlying two types of microtubuledependent nuclear positioning are discussed. ‘MTOCdependent nuclear positioning’ occurs when a nucleus is tightly associated with a microtubule organizing center (MTOC). ‘Nuclear tracking along microtubules’ is analogous to the motor-driven motility of other organelles and occurs when the nucleus lacks an associated MTOC. These two basic types of microtubule-dependent nuclear positioning may cooperate in many proliferating animal cells to achieve proper nuclear positioning. Microtubule polymerization and dynamics, motor proteins, MAPs and specialized sites such as cortical anchors function to control nuclear movements within cells. SUMMARY