Influence of cellular shape on sliding behavior of ciliates.

Some types of ciliates accumulate on solid/fluid interfaces. This behavior is advantageous to survival in nature due to the presence of sufficient nutrition and stable environments. Recently, the accumulating mechanisms of Tetrahymena pyriformis at the interface were investigated. The synergy of the ellipsoidal shape of the cell body and the mechanosensing feature of the cilia allow for cells to slide on interfaces, and the sliding behavior leads to cell accumulation on the interfaces. Here, to examine the generality of the sliding behavior of ciliates, we characterized the behavior of Paramecium caudatum, which is a commonly studied ciliate. Our experimental and numerical results confirmed that P. caudatum also slid on the solid/fluid interface by using the same mechanism as T. pyriformis. In addition, we evaluated the effects of cellular ellipticity on their behaviors near the wall with a phase diagram produced via numerical simulation.

Simple mechanosense and response of cilia motion reveal the intrinsic habits of ciliates.

An important habit of ciliates, namely, their behavioral preference for walls, is revealed through experiments and hydrodynamic simulations. A simple mechanical response of individual ciliary beating (i.e., the beating is stalled by the cilium contacting a wall) can solely determine the sliding motion of the ciliate along the wall and result in a wall-preferring behavior. Considering ciliate ethology, this mechanosensing system is likely an advantage in the single cell's ability to locate nutrition. In other words, ciliates can skillfully use both the sliding motion to feed on a surface and the traveling motion in bulk water to locate new surfaces according to the single "swimming" mission.

Possible mechanisms in the rearrangement of non-yolk cytoplasmic materials during maturation of theXenopus laevis oocyte.

Using the monoclonal antibody (MoAb) Xa5B6 as probe, the authors examined the mechanisms of cytoplasmic rearrangement occurring during maturation of theXenopus oocyte. The antigen molecules recognized by the MoAb are arranged in radial striations of the oocyte cytoplasm. The radial striations were disorganized in vitro by progesterone treatment, and the antigen molecules were uniformly distributed, predominantly in the animal hemisphere. Even when the germinal vesicle was mechanically removed or when germinal vesicle breakdown was suppressed in a K+-free medium, progesterone induced a disorganization of the radial striations. This progesterone-induced disorganization was inhibited by the protein synthesis inhibitor cycloheximide. When full-sized oocytes were treated with cytochalasin B, the radial striations were also disorganized, but the antigen molecules did not disperse into the large mass. Colchicine treatment had little effect. Antigen molecules were no longer arranged in radial striations and were completely dispersed when the oocyte was simultaneously treated with both drugs. These results indicate that the two compartments in the oocyte cytoplasm, the yolk-free cytoplasm and yolk column, are organized by different types of cytoskeletal system. It is also suggested that the maturation-promoting factor (MPF) activated during progesterone-induced maturation disrupts these cytoskeletal systems and disorganizes the radial striations.

Dynamic distribution of region-specific maternal protein during oogenesis and early embryogenesis of Xenopus laevis.

For analysing spatial distribution of maternal proteins in an amphibian egg, monoclonal antibodies specific to certain regions were raised. One monoclonal antibody was found (MoAB Xa5B6) which reacted specifically with the animal hemisphere of the mature Xenopus laevis egg. The maternal protein that reacted with the MoAb Xa5B6 was shown to be distributed asymmetrically along the dorso-ventral axis in the upper region of the equatorial zone of the fertilized egg. At late blastula stage, the antigen protein could be observed clearly in both the marginal zone and animal cap. It was localized predominantly in mesodermal and ectodermal cells of late neurula embryos. The Xa5B6 antigen accumulated during oogenesis. The distribution pattern of maternal protein was remarkably different in the developmental stages of the oocyte. The pattern in the mature oocyte was completely different from that of the immature egg in which the antigen was located in the radial striations of the oocyte cytoplasm. After maturation, the distribution pattern changed drastically to an animal-vegetal polarization and the striation labellings were no longer observed. By Western blot examination, it was confirmed that the amounts of antigen protein were constant during early embryogenesis and the mesoectoderm contained a greater amount of antigens than the endoderm at late blastula. The antibody detected two bands of approximately 70 × 103 and 30 × 103 Mr by Western blot analysis. The latter molecule may possibly be a degrading moiety of the former. The results were discussed in relation to establishment of animal-vegetal (A/V) and dorso-ventral (D/V) polarization at the molecular level.