Dynamic aspects of the cellular organization in a large amoeboid cell are discussed based on the following new findings in the plasmodium of the true slime mold. Upon stimulation, a large plasmodium breaks temporarily into pieces, each containing either about 8 or 4 nuclei. The rhythmic streaming of the protoplasm emerges only when the plasmodial size is larger than the critical value. This bifurcation among dynamic states is compared to that in the feeding behavior by a placozoan, the most primitive multi-cellular organism.
The reversible and stable binding of dioxygen to the heme iron (II) is the basis of myoglobin and hemoglobin functions. During reversible oxygen binding, however, the oxygenated form of myoglobin or hemoglobin is oxidized easily to the ferric (III) met-form with generation of the superoxide anion. Thus, stability property of each oxygenated form is of particular importance in vivo, since the iron (III) species cannot bind dioxygen and is therefore physiologically inactive. With special emphasis on the possible roles of the distal histidine, this overview represents a compendium for the molecular mechanism of autoxidation for myoglobin and hemoglobin molecules.
Long term potentiation (LTP) of synaptic transmission has been considered a cellular mechanism for learning and memory. Pharmacological blockade of synaptic receptors or recent gene-targeting approaches gave evidence to support the hypothesis. However, modifiable synapses are generally embedded deep in complex circuits and many neurons participate in a learning behavior. We first demonstrated a link between LTP and behavioral learning by using a simple circuit for goldfish escape behavior: a single spike of one of the paired Mauthner cells in hindbrain initiates the fast escape response. Repeated sound stimuli to the fish induce LTP of the feedforward inhibition of the M-cell from the auditory nerve and long-lasting desensitization of the escape behavior.
Inner-arm dynein subspecies c (dynein c) of Chlamydomonas flagella is the single-headed dynein which is capable of generating force on microtubules. We recently found that dynein c is a processive motor: a single molecule of dynein c is required to move a microtubule more than 1 μm. However, the duty ratio of dynein c, i.e. the proportion of strongly attached to total ATPase cycle, was estimated to be ca. 14%. This feature is distinct from that of kinesin which is known to be a two-headed processive motor with the higher duty ratio.
Macromolecules such as proteins or nucleic acids have great potentialities as new "drugs" for the treatment of various diseases. To realize the efficient therapy using macromolecules in the near future, it is required to understand the intracellular fate and to develop the multi-functional carrier system for the regulation of the intracellular trafficking. So far, many efforts have been dedicated to optimize the delivery system of macromolecules. I describe here the intracellular fate of macromolecules delivered with carrier and introduce many approaches for the regulation of the intracellular trafficking of macromolecules, especially for gene therapy.