Sex-inducing effect of a hydrophilic fraction on reproductive switching in the planarian Dugesia ryukyuensis (Seriata, Tricladida)

Background

Insects are known to rely on terrestrial landmarks for navigation. Landmarks are used to chart a route or pinpoint a goal. The distant panorama, however, is often thought not to guide navigation directly during a familiar journey, but to act as a contextual cue that primes the correct memory of the landmarks.

Results

We provided Melophorus bagoti ants with a huge artificial landmark located right near the nest entrance to find out whether navigating ants focus on such a prominent visual landmark for homing guidance. When the landmark was displaced by small or large distances, ant routes were affected differently. Certain behaviours appeared inconsistent with the hypothesis that guidance was based on the landmark only. Instead, comparisons of panoramic images recorded on the field, encompassing both landmark and distal panorama, could explain most aspects of the ant behaviours.

Conclusion

Ants navigating along a familiar route do not focus on obvious landmarks or filter out distal panoramic cues, but appear to be guided by cues covering a large area of their panoramic visual field, including both landmarks and distal panorama. Using panoramic views seems an appropriate strategy to cope with the complexity of natural scenes and the poor resolution of insects' eyes. The ability to isolate landmarks from the rest of a scene may be beyond the capacity of animals that do not possess a dedicated object-perception visual stream like primates.     

ATP competitive protein kinase C inhibitors demonstrate distinct state-dependent inhibition

We previously reported that some ATP competitive protein kinase C (PKC) inhibitors are either competitive or uncompetitive inhibitors with respect to substrate peptides. In this report, we demonstrate how the interactions between PKC and inhibitors change PKC activation kinetics. A substrate competitive inhibitor, bisindolylmaleimide I, targets activated PKC and stabilizes PKC in the activated conformation. This leads to transient activation and prolonged deactivation of PKC in the presence of bisindolylmaleimide I. In contrast, an uncompetitive substrate inhibitor, bisindolylmaleimide IV, targets quiescent PKC and stabilizes PKC in the quiescent conformation, which generates slower activation and suppressed translocation upon activation of PKC.     

Electrochemical studies of danthron and the DNA-danthron interaction

Danthron is an important natural occurring component in laxative drugs. In this paper, electrochemical investigation of danthron and its interaction with DNA is reported. Via the electrochemical approach assisted by ultraviolet-visible (UV-Vis) spectroscopy, we have proved that danthron intercalates into DNA strands forming some nonelectroactive complexes, which results in the decrease of redox peak currents of danthron. In addition, the decrease of the peak currents is proportional to the concentration of DNA. The difference between the interaction of danthron with double-stranded DNA (dsDNA) and with single-stranded DNA (ssDNA) has also been studied. This character implies the potential of danthron to discriminate dsDNA and ssDNA.     

Ontogeny of the antigen-reactive lymph follicle-forming capacity of the popliteal lymph node in neonatal mice

The ontogenetic development of the reactive lymph follicle-forming capacity of the popliteal lymph node was investigated immunohistochemically in young mice which had received a single injection of hemocyanin (KLH) in a rear footpad at a predetermined age (between 1 and 21 days). The mice were sacrificed at various intervals after injection. In non-stimulated young mice, primary lymph follicles first appeared in the popliteal node at 11 days of age. When KLH was given to 7-day-old or older mice, each draining popliteal node showed a marked increase in B lymphocytes in the extrafollicular zone 3 days after injection and produced a number of "new" lymph follicles outside the pre-existing follicles over the next few days. In mice injected at 2-4 days of age, these nodes showed an increase in B lymphocytes in the outer cortex and had produced several lymph follicles by 8 days of age. The number of lymph follicles produced by each node tended to increase in line with age at injection. These results indicate that neonatal popliteal nodes become able to produce lymph follicles in response to exogenous antigens some time before ontogenetically developing follicles appear. The formation of new lymph follicles observed in draining popliteal nodes after KLH injection at an early postnatal age is discussed in relation to the ontogenetic development of stromal cells (precursors of follicular dendritic cells) that are capable of interacting with B lymphocytes and the extent of B lymphocyte influx into the node induced by KLH stimulation.     

Molecular design, chemical synthesis, and evaluation of cytosine-carbohydrate hybrids for selective recognition of a single guanine bulged duplex DNA

The designed cytosine-carbohydrate hybrid molecule selectively recognized and stabilized the bulged duplex DNA possessing the complementary bulged DNA base, guanine, while the nucleotide base itself did not exhibit any such ability. It was also found that the assistance of the carbohydrate to stabilize the interaction between the nucleotide base and the complementally bulge DNA base is very helpful for the selective recognition and stabilization of the single-bulged duplex DNA.     

Comparative study of eye defective worm 'menashi' and regenerating wild-type in planarian, Dugesia ryukyuensis

Inbreeding of the sexualized planarian, Dugesia ryukyuensis, produces eye-defective worms, menashi, in the F1 population. To study the effects of this mutation on the eye, we observed the eye-region of menashi using electron microscopy and compared it with the regenerating eye in wild-type worms. The intact eye of wild-type planarians consisted of a few pigment cells and a number of visual cells. Pigment cells containing spherically-shaped electron-dense melanosomes contacted each other and enclosed rhabdomes of visual cells. Rhabdomes had numerous tubular microvilli extending radially and touching the pigment cells. However, in menashi, various lengths of tubular microvilli were irregularly distributed near the pigment cells, which contained numerous electron-lucent premelanosomes, and no adhesive structures were found between the pigment cells. The premelanosomes of menashi were equal in size to those seen after 2 days of regeneration in wild-type planarians and were similar in maturation to those found after 3 days of regeneration in wild-type planarian. These results suggest that menashi is defective in the mechanism(s) of developing pigment granules and constructing visual cells. These findings also suggest that pigment cells in menashi are defective in the mechanism(s) involved with cell adhesion.     

Distinct enzyme combinations in AKAP signalling complexes permit functional diversity

Specificity in cell signalling can be influenced by the targeting of different enzyme combinations to substrates. The A-kinase anchoring protein AKAP79/150 is a multivalent scaffolding protein that coordinates the subcellular localization of second-messenger-regulated enzymes, such as protein kinase A, protein kinase C and protein phosphatase 2B. We developed a new strategy that combines RNA interference of the endogenous protein with a protocol that selects cells that have been rescued with AKAP79/150 forms that are unable to anchor selected enzymes. Using this approach, we show that AKAP79/150 coordinates different enzyme combinations to modulate the activity of two distinct neuronal ion channels: AMPA-type glutamate receptors and M-type potassium channels. Utilization of distinct enzyme combinations in this manner provides a means to expand the repertoire of cellular events that the same AKAP modulates.     

Anti-tumor-initiating effects of monascin, an azaphilonoid pigment from the extract of Monascus pilosus fermented rice (red-mold rice)

Monascin (1) constitutes one of the azaphilonoid pigments in the extracts of Monascus pilosus-fermented rice (red-mold rice). Compound 1 was evaluated for its anti-tumor-initiating activity via oral administration on the two-stage carcinogenesis of mouse skin tumor induced by peroxynitrite (ONOO-; PN) or by ultraviolet light B (UVB) as an initiator and 12-O-tetradecanoylphorbol-13-acetate (TPA) as a promoter. Compound 1 exhibited marked inhibitory activity on both PN- and UVB-induced mouse skin carcinogenesis tests. These findings suggest that compound 1 may be valuable as potential cancer chemopreventive agent in chemical and environmental carcinogenesis.     

Heme regulates allosteric activation of the Slo1 BK channel

Large conductance calcium-dependent (Slo1 BK) channels are allosterically activated by membrane depolarization and divalent cations, and possess a rich modulatory repertoire. Recently, intracellular heme has been identified as a potent regulator of Slo1 BK channels (Tang, X.D., R. Xu, M.F. Reynolds, M.L. Garcia, S.H. Heinemann, and T. Hoshi. 2003. Nature. 425:531-535). Here we investigated the mechanism of the regulatory action of heme on heterologously expressed Slo1 BK channels by separating the influences of voltage and divalent cations. In the absence of divalent cations, heme generally decreased ionic currents by shifting the channel's G-V curve toward more depolarized voltages and by rendering the curve less steep. In contrast, gating currents remained largely unaffected by heme. Simulations suggest that a decrease in the strength of allosteric coupling between the voltage sensor and the activation gate and a concomitant stabilization of the open state account for the essential features of the heme action in the absence of divalent ions. At saturating levels of divalent cations, heme remained similarly effective with its influence on the G-V simulated by weakening the coupling of both Ca(2+) binding and voltage sensor activation to channel opening. The results thus show that heme dampens the influence of allosteric activators on the activation gate of the Slo1 BK channel. To account for these effects, we consider the possibility that heme binding alters the structure of the RCK gating ring and thereby disrupts both Ca(2+)- and voltage-dependent gating as well as intrinsic stability of the open state.