One-Dimensional Brownian Motion of Charged Nanoparticles along Microtubules: A Model System for Weak Binding Interactions

Various proteins are known to exhibit one-dimensional Brownian motion along charged rodlike polymers, such as microtubules (MTs), actin, and DNA. The electrostatic interaction between the proteins and the rodlike polymers appears to be crucial for one-dimensional Brownian motion, although the underlying mechanism has not been fully clarified. We examined the interactions of positively-charged nanoparticles composed of polyacrylamide gels with MTs. These hydrophilic nanoparticles bound to MTs and displayed one-dimensional Brownian motion in a charge-dependent manner, which indicates that nonspecific electrostatic interaction is sufficient for one-dimensional Brownian motion. The diffusion coefficient decreased exponentially with an increasing particle charge (with the exponent being 0.10 k_BT per charge), whereas the duration of the interaction increased exponentially (exponent of 0.22 k_BT per charge). These results can be explained semiquantitatively if one assumes that a particle repeats a cycle of binding to and movement along an MT until it finally dissociates from the MT. During the movement, a particle is still electrostatically constrained in the potential valley surrounding the MT. This entire process can be described by a three-state model analogous to the Michaelis-Menten scheme, in which the two parameters of the equilibrium constant between binding and movement, and the rate of dissociation from the MT, are derived as a function of the particle charge density. This study highlights the possibility that the weak binding interactions between proteins and rodlike polymers, e.g., MTs, are mediated by a similar, nonspecific charge-dependent mechanism.     

Pheromonal cross-attraction in true bugs (Heteroptera): attraction of Piezodorus hybneri (Pentatomidae) to its pheromone versus the pheromone of Riptortus pedestris (Alydidae)

We investigated the attractiveness of a synthetic form of the pheromone of the soybean stink bug, Piezodorus hybneri (Gmelin), under field conditions, and compared it with that of (E)-2-hexenyl (E)-2-hexenoate, a pheromone component of a competitor, Riptortus pedestris (Fabricius). Many adult stink bugs were attracted to traps baited with 100 mg of the synthetic pheromone (1: 1: one mixture of β-sesquiphellandrene, (R)-15-hexadecanolide, and methyl (Z)-8-hexadecenoate), but few were attracted to 1 or 10 mg. More than twice as many females as males were attracted to this male-produced pheromone. None of the individual pheromone components (30 mg) attracted conspecifics. In summer (June-July), when field P. hybneri were not in diapause, (E)-2-hexenyl (E)-2-hexenoate was more attractive to P. hybneri than the synthetic pheromone. The sex ratio of the adults attracted to the synthetic pheromone was highly female-biased, yet almost equal numbers of both sexes were attracted to (E)-2-hexenyl (E)-2-hexenoate. Most females attracted to both attractants were mated and had mature ovaries. However, adults attracted to (E)-2-hexenyl (E)-2-hexenoate were likely to have less food in their stomach than those attracted to the synthetic pheromone. In late autumn (October-November), when the bugs were in reproductive diapause, both attractants attracted many sexually immature female and male adults that had well-developed fat body. The synthetic pheromone also attracted a large number of conspecific nymphs. These results suggest that P. hybneri pheromone and R. pedestris pheromone component, respectively, have different functions for P. hybneri. The male-produced pheromone system of P. hybneri seems to be sex-related but to have other roles.     

CHANGE OF UBIQUITINATED PROTEINS DURING THE CELL CYCLE IN CHLAMYDOMONAS (CHLOROPHYTA)1

Changes in the amount of heat shock-related ubiquitinated proteins in Chlamydomonas were investigated during the cell cycle and gamete induction. In a division-synchronized culture induced by periodic illumination, the amount of the 28-kDa ubiquitinated protein increased during the dark phase. This increase correlated with the increase of total DNA. Such an increase was repressed when nuclear DNA replication was inhibited with aphidicolin. These results suggest that ubiquitination to form the 28-kDa protein is involved in nuclear DNA replication or during the cell cycle. The amount of 31-kDa ubiquitinated protein gradually increased throughout the light phase and decreased in the dark phase. The amount of 28-kDa ubiquitinated protein also increased during gamete induction caused by nitrogen starvation, while that of the 31-kDa did not. These results suggest that the change of ubiquitination of 28-kDa protein mat play a fundamental role in the cell cycle and gamete induction in Chlamydomonas.     

Mechanism of rapid-phase insulin response to elevation of portal glucose concentration

The hepatoportal region is important for glucose sensing; however, the relationship between the hepatoportal glucose-sensing system and the postprandial rapid phase of the insulin response has been unclear. We examined whether a rapid-phase insulin response to low amounts of intraportal glucose infusion would occur, compared that with the response to intrajugular glucose infusion in conscious rats, and assessed whether this sensing system was associated with autonomic nerve activity. The increases in plasma glucose concentration did not differ between the two infusions at 3 min, but the rapid-phase insulin response was detected only in the intraportal infusion. A sharp and rapid insulin response was observed at 3 min after intraportal infusion of a small amount of glucose but not after intrajugular infusion. Furthermore, this insulin response was also induced by intraportal fructose infusion but not by nonmetabolizable sugars. The rapid-phase insulin response at 3 min during intraportal infusion did not differ between rats that had undergone hepatic vagotomy or chemical sympathectomy with 6-hydroxydopamine compared with control rats, but this response disappeared in rats that had undergone chemical vagotomy with atropine. We conclude that the elevation of glucose concentration in the hepatoportal region induced afferent signals from undetectable sensors and that these signals stimulate pancreas to induce the rapid-phase insulin response via cholinergic nerve action.     

Evolution of indirect reciprocity in groups of various sizes and comparison with direct reciprocity

Recently many studies have investigated the evolution of indirect reciprocity through which cooperative action is returned by a third individual, e.g. individual A helped B and then receives help from C. Most studies on indirect reciprocity have presumed that only two individuals take part in a single interaction (group), e.g. A helps B and C helps A. In this paper, we investigate the evolution of indirect reciprocity when more than two individuals take part in a single group, and compare the result with direct reciprocity through which cooperative action is directly returned by the recipient. Our analyses show the following. In the population with discriminating cooperators and unconditional defectors, whether implementation error is included or not, (i) both strategies are evolutionarily stable and the evolution of indirect reciprocity becomes more difficult as group size increases, and (ii) the condition for the evolution of indirect reciprocity under standing reputation criterion where the third individuals distinguish between justified and unjustified defections is more relaxed than that under image scoring reputation criterion in which the third individuals do not distinguish with. Furthermore, in the population that also includes unconditional cooperators, (iii) in the presence of errors in implementation, the discriminating strategy is evolutionarily stable not only under standing but also under image scoring if group size is larger than two. Finally, (iv) in the absence of errors in implementation, the condition for the evolution of direct reciprocity is equivalent to that for the evolution of indirect reciprocity under standing, and, in the presence of errors, the condition for the evolution of direct reciprocity is very close to that for the evolution of indirect reciprocity under image scoring.     

Sequence variation in the Tbx4 gene in marine mammals

The amino-acid sequences of the T-domain region of the Tbx4 gene, which is required for hindlimb development, are 100% identical in humans and mice. Cetaceans have lost most of their hindlimb structure, although hindlimb buds are present in very early cetacean embryos. To examine whether the Tbx4 gene has the same function in cetaceans as in other mammals, we analyzed Tbx4 sequences from cetaceans, dugong, artiodactyls and marine carnivores. A total of 39 primers were designed using human and dog Tbx4 nucleotide sequences. Exons 3, 4, 5, 6, 7, and 8 of the Tbx4 genes from cetaceans, artiodactyls, and marine carnivores were sequenced. Non-synonymous substitution sites were detected in the T-domain regions from some cetacean species, but were not detected in those from artiodactyls, the dugong, or the carnivores. The C-terminal regions contained a number of non-synonymous substitutions. Although some indels were present, they were in groups of three nucleotides and therefore did not cause frame shifts. The dN/dS values for the T-domain and C-terminal regions of the cetacean and artiodactylous Tbx4 genes were much lower than 1, indicating that the Tbx4 gene maintains it function in cetaceans, although full expression leading to hindlimb development is suppressed.