There have been many studies to determine extrinsic factors that may regulate the neuronal migration and growth of axons and dendrites. However, the intracellular mechanism, especially the regulation of cytoskeleton, has not been clarified. It has been reported that actin filament crosslinking protein, MARCKS, play roles in cell motility through cytoskeletal rearrangement accompanied by rapid, PKC-dependent phosphorylation. Recently, we have demonstrated that neuron-specific actin binding protein, drebrin, changed the stability and distribution of microfilaments within the fibroblast and formed highly-branched dendrite-like cell processes from their cell perimeters. It has also been reported that overexpression of microtubule associated protein, tau, in a fibroblast induced long axon-like cellular processes. This review will focus on dynamic regulations of the microfilament by drebrin and those of the microtubules by MAP2 and tau. Since all kinds of cytoskeletons are related to each other, the binding ability of neurofilament H to microtubules and that of MAP2 to neurofilaments were also discussed.
The human scalp hair is a useful tissue that retains the past dosage history over a rather long period of time, acting like a “tape-recorder”. It should be emphasized that the sampling of hair can be made noninvasively by cutting a few to several pieces of hair nearest to the scalp. Because the hair continues to grow at the rate of about 1 cm/month, each 1-cm hair length contains the drug corresponding to the amount ingested over a 1-month period when the hair is cut into 1-cm lengths successively from the scalp end. However, the hair growth rate is variable both within and between individuals, and the hair has its own growth cycle, i.e., 2 to 8 years or more of the growing stage and a few months of the resting stage. Therefore, the validity of the obtained results must always be considered cautiously, especially in relation to whether a resting phase hair might have been sampled. For obtaining information on the growth rate and stage of a hair, a drug that can be detected in the hair even after a short-term exposure to the drug has been found. These drugs are antimicrobial quinolones such as ofloxacin. By analyzing the axial distribution of ofloxacin along the hair shaft, we can expect to determine the so-called “tape-speed” and “uniformity of tape-running” of a single hair.