Class V myosin motors are thought to transport organelles along actin filaments. Myosin Va functions in melanosome trafficking, docking in a manner dependent on the GTPase Rab27a. Less is known about myosin Vb (Myo5b),although it has been shown to interact with Rab11a and is implicated in transferrin receptor recycling. Olga Rodriguez and Richard Cheney now report the cloning and characterization of a third member of this class, myosin Vc(Myo5c). Myo5c is ubiquitously expressed but particularly abundant in epithelial cells. The authors find that overexpression of a dominant negative Myo5c construct disrupts membrane trafficking of the transferrin receptor via a Rab8-containing compartment to which Myo5c localizes. Interestingly,dominant negative Myo5b affects recycling of transferrin receptor via Rab11a-containing compartments. Since dominant negative Myo5c appears to have no effect on this latter pathway, Rodriguez and Cheney suggest that two independent mechanisms for transferrin receptor trafficking exist: a Rab11a-Myo5b pathway and a Rab8-Myo5c pathway. They suggest that the latter is probably important in polarized epithelial cells, in which Myo5c is most abundantly expressed.
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