MECHANISMS OF NUCLEAR POSITIONING - COMMENTARY

The mechanisms underlying two types of microtubule-dependent nuclear p ositioning are discussed. 'MTOC-dependent nuclear positioning' occurs when a nucleus is tightly associated with a microtubule organizing cen ter (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-depende nt nuclear positioning may cooperate in many proliferating animal cell s to achieve proper nuclear positioning. Microtubule polymerization an d dynamics, motor proteins, MAPs and specialized sites such as cortica l anchors function to control nuclear movements within cells.