Kinesin cross-bridges between neurosecretory granules and microtubules in the mouse neurohypophysis.

Neurosecretory granules are conveyed along microtubules in the neurohypophysial axon. By both quick-freeze deep-etch and thin section electron microscopies, we found cross-bridges between the granules and microtubules. The length of the cross-bridges (mean 26.6 +/- 15.2 nm) was not uniform, and its histogram was multi-phasic showing the highest peak around 20 nm and several lower peaks in the range of 40-100 nm. This implies that cross-bridges are complexes of several kinds of constituents. Immunofluorescence microscopy showed the expression of a motor protein kinesin in the mouse neurohypophysis. Immunoelectron microscopy detected kinesin at the contact sites of neurosecretory granules to microtubules. These results suggest that kinesin is a major component of the cross-bridges, and involved in the neurosecretory granule transportation.