Stimulation-dependent intraspinal microtubules and synaptic failure in Alzheimer's disease: a review.

There are many microtubules in axons and dendritic shafts, but it has been thought that there were fewer microtubules in spines. Recently, there have been four reports that observed the intraspinal microtubules. Because microtubules originate from the centrosome, these four reports strongly suggest a stimulation-dependent connection between the nucleus and the stimulated postsynaptic membrane by microtubules.

Amyloid beta: a putative intra-spinal microtubule-depolymerizer to induce synapse-loss or dentritic spine shortening in Alzheimer's disease.

A loss or shortening of dendritic spines has been described in patients with neurodegenerative disorders such as Alzheimer's disease, but the underlying mechanisms are poorly understood. Recently, there have been four reports of capture of the plus-ends of microtubules in the dendritic spines. One report, based on acute hippocampal slices that were fixed by a microtubule preserving process after LTP-inducing stimulation, showed that microtubules of the dendritic shaft ramified into spines in a manner that was specific to the stimulated postsynaptic membranes.

Microtubules to form memory.

Microtunbule-depolymerizing agents cause amnesia. Some signal translocations to the stimulated postsynaptic membrane are essential for inducing LTP in CA1 neurons like AMPA receptors, CaMKII and mRNA. On the other hand, LTP requires protein synthesis and gene expression.

Microinjected F-actin into dividing newt eggs moves toward the next cleavage furrow together with Ca2+ stores with inositol 1,4,5-trisphosphate receptor in a microtubule- and microtubule motor-dependent manner.

It has been reported that F-actin is transported to the presumptive cleavage furrow along the cortex during anaphase-cytokinesis, an event termed cortical actin flow in animal cultured cells. The motor source has remained unknown. We reported that Ca2+ stores with IP3 receptor (IP3R) was re-distributed from the polar cortex during metaphase to the presumptive cleavage furrow just before the onset of furrowing, and that Ca2+ stores with IP3R microinjected into dividing newt eggs moved toward the presumptive cleavage furrow during anaphase-cytokinesis in a microtubule-dependent manner, and that Ca2+ store-enriched microsome fractions induced the cleavage furrow as the putative cleavage stimulus.