REGULATION OF ORGANELLE TRANSPORT - LESSONS FROM COLOR-CHANGE IN FISH

Organelles transported along microtubules are normally moved to precis e locations within cells. For example, synaptic vesicles are transport ed to the neuronal synapse, the Golgi apparatus is generally found in a perinuclear location, and the membranes of the endoplasmic reticulum are actively extended to the cell periphery. The correct positioning of these organelles depends on microtubules and microtubule motors. Me lanophores provide an extreme example of organized organelle transport . These cells are specialized to transport pigment granules, which are coordinately moved towards or away from the cell center, and result i n the cell appearing alternately light or dark. Melanophores have prov ed to be an ideal system for studying the mechanisms by which the cell controls the direction of its organelle transport. Pigment granule di spersion (the movement away from the cell center) requires protein pho sphorylation, while pigment aggregation (the movement towards the cell center) requires protein dephosphorylation. The target of this phosph orylation and dephosphorylation event is a protein that interacts with the microtubule motor protein, kinesin. Thus, the direction of organe lle transport along microtubules may be regulated by controlling the a ctivity of a microtubule motor.