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Bell-shaped Curve (bell-shaped + curve)
Selected AbstractsCooperative activity of multiple upper layer proteins for thalamocortical axon growthDEVELOPMENTAL NEUROBIOLOGY, Issue 3 2008Takuro Maruyama Abstract During development, sensory thalamocortical (TC) axons grow into the neocortex and terminate primarily in layer 4. To study the molecular mechanism that underlies lamina-specific TC axon termination, we investigated the responsiveness of TC axons to ephrin-A5, semaphorin-7A (Sema7A) and kit ligand (KL), which are expressed in the upper layers of the developing cortex. Dissociated cells of the dorsal thalamus from embryonic rat brain were cultured on dishes that were coated with preclustered Fc-tagged extracellular domains of these molecules. Each protein was found to promote TC axon growth in a dose-dependent fashion of a bell-shaped curve. Any combination of the three proteins showed a cooperative effect in lower concentrations but not in higher concentrations, suggesting that their growth-promoting activities act in a common pathway. The effect of spatial distributions of these proteins was further tested on a filter membrane, in which these proteins were printed at a size that recapitulates the scale of laminar thickness in vivo, using a novel protein-printing technique, Simple-To-mAke Micropore Protein-Printing (STAMP2) method. The results demonstrated that TC axons grew massively on the laminin-coated region but were prevented from invading the adjacent ephrin-A5-printed region, suggesting that TC axons detect relative differences in the growth effect between these regions. Moreover, the inhibitory action of ephrin-A5 was enhanced by copresence with KL and Sema7A. Together, these results suggest that the lamina-specific TC axon targeting mechanism involves growth-inhibitory activity by multiple molecules in the upper layers and detection in the molecular environments between the upper and deep layers. © 2007 Wiley Periodicals, Inc. Develop Neurobiol, 2008 [source] Significant activity of a modified ribozyme with N7-deazaguanine at G10.1: the double-metal-ion mechanism of catalysis in reactions catalysed by hammerhead ribozymesGENES TO CELLS, Issue 8 2000Yuka Nakamatsu Background Several reports have appeared recently of experimental evidence for a double-metal-ion mechanism of catalysis in reactions catalysed by hammerhead ribozymes. In one case, hammerhead ribozyme-mediated cleavage was analysed as a function of the concentration of La3+ ions in the presence of a fixed concentration of Mg2+ ions so that the role of metal ions that are directly involved in the cleavage reaction could be monitored. The resultant bell-shaped curve for activation of cleavage was used to support the proposed double-metal-ion mechanism of catalysis. However, other studies have demonstrated that the binding of a metal ion (the most conserved P9 metal ion) to the pro-Rp oxygen (P9 oxygen) of the phosphate moiety of nucleotide A9 and to the N7 of nucleotide G10.1 is critical for efficient catalysis, despite the large distance (,20 Å) between the P9 metal ion and the labile phosphodiester group in the ground state. In fact, it was demonstrated that an added Cd2+ ion binds first to the pro-Rp phosphoryl P9 oxygen but not with the pro-Rp phosphoryl oxygen at the cleavage site. Results In earlier discussions, it was difficult to completely exclude the possibility that La3+ ions might have replaced the P9 metal ion and, as a result, created conditions represented by the bell-shaped curve. In order to clarify this situation, we examined a chemically synthesized hammerhead ribozyme (7-deaza-R34) that included a minimal modification, namely, an N7-deazaguanine residue in place of G10.1. We compared the kinetic properties of this ribozyme with those of the parental ribozyme (R34). Kinetic analysis revealed that, unlike the cases of added Cd2+ ions, the added La3+ ions did not replace the pre-existing P9 metal ion, and that the replacement of N7 by C7 at G10.1 reduced the catalytic activity to a limited extent. This result indicates that the binding of a Mg2+ ion to N7 at G10.1 is catalytically important but not indispensable. Most importantly, 7-deaza-R34 also yielded a bell-shaped curve upon addition of La3+ ions to the reaction mixture. Conclusions Since the data based on our experiments with 7-deaza-R34 are completely free from potential artefacts, due to the binding of a La3+ ion to N7 at G10.1, our results, that 7-deaza-R34 yielded a bell-shaped curve following the addition of La3+ ions to the Mg2+ -background reaction mixture, strongly supports the proposal that a double-metal-ion mechanism is operative in the cleavage reaction which is catalysed by hammerhead ribozymes. [source] Estrogenic activity of Nigella damascena extracts, evaluated using a recombinant yeast screenPHYTOTHERAPY RESEARCH, Issue 5 2002E. Agradi Abstract We used the yeast estrogen screen (YES) containing a human estrogen receptor to evaluate the estrogenic activity of extracts obtained from Nigella damascena seeds. Alcohol extracts obtained by direct extraction of seeds showed a low estrogenic activity, while the alcohol extract obtained after extraction with solvents of increasing polarity showed a strong estrogenic activity. This suggests the presence in Nigella of polar components whose activity can be clearly demonstrated after previous elimination of interacting apolar components that may mask the activity of more polar components. The response of both alcohol fractions follow a bell-shaped curve indicating a concentration-dependent relationship. Copyright © 2002 John Wiley & Sons, Ltd. [source] Butterfly life history and temperature adaptations; dry open habitats select for increased fecundity and longevityJOURNAL OF ANIMAL ECOLOGY, Issue 1 2005BENGT KARLSSON Summary 1Evidence suggests that changes of temperature-related performance curves can trigger a selective response in life-history traits. Hence, it should be expected that insects adapted to different temperature regimes should exhibit optimal performance at the temperature to which they are adapted. 2To test this idea we investigated how fecundity and longevity are influenced by ambient temperatures in a set of satyrine butterflies adapted to live in dry open landscapes or in closed forest landscapes, respectively, by keeping egg-laying adult females at five different constant temperatures ranging between 20 and 40 °C. 3We studied four species, two of which are confined to dry and hot open habitats, namely the grayling (Hipparchia semele) and the small heath (Coenonympha pamphilus), and two of which are shade dwelling, namely the ringlet (Aphantopus hyperantus) and the speckled wood butterfly (Pararge aegeria). 4As predicted, the results showed that lifetime fecundity exhibited bell-shaped curves in relation to temperature with the open landscape group peaking at a higher temperature, 30 °C, compared with the shade-dwelling group that peaked at 25 °C. Longevity decreased with increasing temperatures among all species, but the open landscape living species survived better at higher temperatures. Moreover, although the magnitude of reproductive effort measured as lifetime egg mass did not differ between the two ecological groups, lifetime fecundity did with open landscape species laying more and smaller eggs than the shade-dwelling species. 5This difference in life-history character traits suggests either that dry and relatively warm open habitats open life-history opportunities in terms of higher fecundity and longevity that remain closed to butterflies adapted to cooler temperatures, or that life in dry open habitats actively selects for higher fecundity and survival as a result of increased offspring mortality. [source] | ||||||||||