Moving on to the cargo problem of microtubule-dependent motors in neurons.

Vigorous investigation has finally begun to shed light on the cargo problem of the microtubule-dependent motors, kinesin and dynein superfamily proteins. Biochemical observations have suggested that the potential cargoes of certain populations of motor proteins seem to be in vesicle-form, each vesicle possessing specific functional marker molecules. In addition to the close relationship between microtubule-dependent motors and cargoes in vesicle-form, kinesin has also been highlighted as an apparent driving force for another cargo in non-vesicle-form, cytoplasmic protein. On the basis of new biophysical and cell-biological evidence, the controversy over the movement of cytoplasmic cargoes has entered a new phase.