Ultrastructure of tubulin paracrystals from sea urchin eggs, with determination of spacings by electron and optical diffraction

Anti-Microtubule Drugs

Small molecule drugs that target microtubules (MTs), many of them natural products, have long been important tools in the MT field. Indeed, tubulin (Tb) was discovered, in part, as the protein binding partner of colchicine. Several anti-MT drug classes also have important medical uses, notably colchicine, which is used to treat gout, familial Mediterranean fever (FMF), and pericarditis, and the vinca alkaloids and taxanes, which are used to treat cancer. Anti-MT drugs have in common that they bind specifically to Tb in the dimer, MT or some other form. However, their effects on polymerization dynamics and on the human body differ markedly. Here we briefly review the most-studied molecules, and comment on their uses in basic research and medicine. Our focus is on practical applications of different anti-MT drugs in the laboratory, and key points that users should be aware of when designing experiments. We also touch on interesting unsolved problems, particularly in the area of medical applications. In our opinion, the mechanism by which any MT drug cures or treats any disease is still unsolved, despite decades of research. Solving this problem for particular drug-disease combinations might open new uses for old drugs, or provide insights into novel routes for treatment.

Antimitotic activity of the pyrimidinone derivative py-09 on sea urchin embryonic development

Chemotherapy is the main cancer treatment and consists of drug administration that interferes with several metabolic pathways, leading to tumor cell death. Antimitotic drugs have a relevant role in chemotherapy. This study aimed to investigate the effect of a pyrimidinone derivative (6-(p-Anisyl)-2-(p-chlorophenyl)-4-oxo-3,4-dihydropyrimidine-5-carbonitrile, Py-09) on sea urchin embryonic development model. The effects of the compound were analyzed on fertilization, embryonic development, mitochondrial membrane potential (ΔΨm), production of reactive oxygen species (ROS) and ABC transporter activity. Py-09 inhibited the fertilization and the embryonic development in a time and dose-dependent pattern, with the maximum effect at 50 μM (EC50=12.5 μM). Py-09 induced the loss of ΔΨm without altering ROS intracellular levels. Morphological changes were observed in the pattern of embryo cleavage (unequal cleavage) and at larval stages (fissures of spicules and pigment cell leakage). We also demonstrated that Py-09 is not an ABC transporter substrate and the derivative does not circumvent the MXR phenomenon. Our study reports--for the first time--the antimitotic activity of Py-09 and stimulates new research on the potential of Py-09 as a pharmacological tool for in vitro studies, as well as its use as a new anticancer drug.

Immunohistochemistry and effect of vinblastine on intracisternal microtubules of the canine neurons

The immuno-histochemical and drug-binding properties of intracisternal microtubules (IMs) in the RER of canine neurons were studied with antitubulin IgG and vinblastine. Specific fluorescence against antitubulin IgG was not detected in the RER in which the IMs were aggregated but was observed in the cytoplasm outside the RER. Injection of vinblastine into the sympathetic ganglion did not change the size, shape or arrangement of IMs in the RER, although typical honeycomb crystals were formed near IM-containing RER. These findings show that the IM does not possess antigenicity to antitubulin IgG and has no vinblastine-binding site. Thus it is suggested that the IM may be a defective or modified microtubule.

Arrangement of protofilaments in two forms of tubulin crystal induced by vinblastine

Tubulin crystals produced by incubation with vinblastine sulphate have been investigated by X-ray diffraction, electron microscopy and density measurement. The results show that crystals produced in vitro from bovine brain tubulin are made of packed helices, each consisting of a single continuous protofilament, whereas crystals produced in vivo in sea urchin eggs are built from pairs of such helices. The symmetry, cell dimensions, percentage protein and composition of the crystals are consistent with either 24 or 30 tubulin monomers per turn of the helix. The sea urchin egg crystals are more highly ordered and thus more suitable for further analysis.

Dynamical electron scattering from negatively stained protein microcrystals

Multislice n-beam dynamical calculations have been carried out at 20 and 15.6 A resolution to simulate the electron scattering from a negatively-stained protein microcrystal using a model based on the crystal structure of E. coli matrix porin. Images at t = 100 A, i.e. the thickness of reconstituted vesicle preparation, correspond to the projected potential of the kinematical structure. The kinematical model is valid at least to t = 500 A, beyond which the projected-image symmetry does not correspond to the actual structure. If a crystallographic residual limit R = 0.20 is imposed, the electron diffraction intensity data correspond to the kinematical data up to t = 700 and 1000 A, respectively, for 15.6 and 20 A resolution.

Heat-induced reversible hexagonal packing of spindle microtubules

Epithelial cells cultured from the lung of the Northwest rough-skinned newt (Taricha granulosa granulosa) were subjected to brief (10-15 min) elevated temperature shocks of 33 degrees-36 degrees C during metaphase. Electron microscope studies on these cells reveal that the spindle microtubules (Mts) are differentially stable to heat treatment. The great majority of nonkinetochore Mts are destroyed within the first few minutes of the shock while kinetochore and adjacent Mts rearrange to form hexagonal closely packed structures before disassembling, the latter occurring only after prolonged heat treatment. The significance and theoretical implications of the formation of hexagonal closely packed Mt structures and of the differential stability of spindle Mts to heating are discussed. The data suggest the existence of one or more heat-sensitive structural component(s) which maintain the individual minimum spacing seen between spindle Mts. To our knowledge, this is the first reported instance of the experimental rearrangement of kinetochore Mts into reversible, hexagonal closely packed bundles.