Über Kunst in Italien im zwölften Jahrhundert

Digitalisat von: 01-03921 - Neumann, Carl: Über Kunst in Italien im zwölften Jahrhunder

The role of the wingless gene in the control of growth and pattern formation during drosophila wing development

Recent work on Drosophila limb development has indicated that short-range interactions between distinctly specified populations of cells (compartments) establish organizing centers at compartment boundaries. These organizing centers direct pattern formation and growth in the developing limbs. In the Drosophila wing imaginal disc, there are at least two such organizing centers, located at the anterior/posterior (A/P) and dorsal/ventral (D/V) compartment boundaries. The genetic hierarchies which establish these organizers are starting to be understood, and it also appears that the key mediators of some of the organizers have been identified. Thus Decapentaplegic (Dpp, a secreted signalling molecule of the TGF-B family) is the mediator of the A/P organizer, while Wingless (DWnt-l, a secreted molecule of the Wnt family) is a key mediator of the D/V organizer. In this thesis, several aspects of Wingless function in the wing imaginal disc are examined. Two regulatory mutations, spadeflag (spdfg) and Sternopleural (Sp), that affect Wingless expression in the wing imaginal disc are characterized. The analysis of the mutation spdfg, together with other data, identifies a role of Wingless as a localized mitogen in the developing wing hinge, and also indicates that cells in different regions of the wing disc respond very differently to the Wingless signal. The mutations spdfg and Sp are also among the tools used to examine the position of Wingless in the genetic hierarchy that establishes and mediates the activity of the D/V organizer. These experiments extend the evidence suggesting that Wingless mediates both short-range and long-range effects of the D/V organizer. Wg does so by controlling the expression domains of different target genes, including the acheate-scute genes, Distal-less and vestigial. Finally, the mechanism by which Wingless mediates the activity of the D/V organizer is examined. The results obtained suggest that Wingless functions as a long-range morphogen

Self-Repelling Elastic Manifolds with Low Dimensional Range

We consider self-repelling elastic manifolds with a domain $[-N,N]^d \cap \mathbb{Z}^d$, that take values in $\mathbb{R}^D$. Our main result states that when the dimension of the domain is $d=2$ and the dimension of the range is $D=1$, the effective radius $R_N$ of the manifold is approximately $N^{4/3}$. This verifies the conjecture of Kantor, Kardar and Nelson [7]. Our results for the case where $d \geq 3$ and $D <d$ give a lower bound on $R_N$ of order $N^{\frac{1}{D} \left(d-\frac{2(d-D)}{D+2} \right)}$ and an upper bound proportional to $N^{\frac{d}{2}+\frac{d-D}{D+2}}$. These results imply that self-repelling elastic manifolds with a low dimensional range undergo a significantly stronger stretching than in the case where $d=D$, which was studied by the authors in [10].Comment: 19 pages. arXiv admin note: substantial text overlap with arXiv:2112.1300

Bound states of PT-symmetric separable potentials

All of the PT-symmetric potentials that have been studied so far have been local. In this paper nonlocal PT-symmetric separable potentials of the form $V(x,y)=i\epsilon[U(x)U(y)-U(-x)U(-y)]$, where $U(x)$ is real, are examined. Two specific models are examined. In each case it is shown that there is a parametric region of the coupling strength $\epsilon$ for which the PT symmetry of the Hamiltonian is unbroken and the bound-state energies are real. The critical values of $\epsilon$ that bound this region are calculated.Comment: 10 pages, 3 figure

Distinct roles of Shh and Fgf signaling in regulating cell proliferation during zebrafish pectoral fin development

<p>Abstract</p> <p>Background</p> <p>Cell proliferation in multicellular organisms must be coordinated with pattern formation. The major signaling pathways directing pattern formation in the vertebrate limb are well characterized, and we have therefore chosen this organ to examine the interaction between proliferation and patterning. Two important signals for limb development are members of the Hedgehog (Hh) and Fibroblast Growth Factor (Fgf) families of secreted signaling proteins. Sonic hedgehog (Shh) directs pattern formation along the anterior/posterior axis of the limb, whereas several Fgfs in combination direct pattern formation along the proximal/distal axis of the limb.</p> <p>Results</p> <p>We used the genetic and pharmacological amenability of the zebrafish model system to dissect the relative importance of Shh and Fgf signaling in regulating proliferation during development of the pectoral fin buds. In zebrafish mutants disrupting the <it>shh </it>gene, proliferation in the pectoral fin buds is initially normal, but later is strongly reduced. Correlating with this reduction, Fgf signaling is normal at early stages, but is later lost in <it>shh </it>mutants. Furthermore, pharmacological inhibition of Hh signaling for short periods has little effect on either Fgf signaling, or on expression of G1- and S-phase cell-cycle genes, whereas long periods of inhibition lead to the downregulation of both. In contrast, even short periods of pharmacological inhibition of Fgf signaling lead to strong disruption of proliferation in the fin buds, without affecting Shh signaling. To directly test the ability of Fgf signaling to regulate proliferation in the absence of Shh signaling, we implanted beads soaked with Fgf protein into <it>shh </it>mutant fin buds. We find that Fgf-soaked beads rescue proliferation in the pectoral find buds of <it>shh </it>mutants, indicating that Fgf signaling is sufficient to direct proliferation in zebrafish fin buds in the absence of Shh.</p> <p>Conclusion</p> <p>Previous studies have shown that both Shh and Fgf signaling are crucial for outgrowth of the vertebrate limb. The results presented here show that the role of Shh in this process is indirect, and is mediated by its effect on Fgf signaling. By contrast, the activity of the Fgf pathway affects proliferation directly and independently of its effect on Shh. These results show that Fgf signaling is of primary importance in directing outgrowth of the limb bud, and clarify the role of the Shh-Fgf feedback loop in regulating proliferation.</p

Kinetic calibration of the calcium indicator arsenazo III. I. Stopped-flow spectroscopy

Clemen S, Rabl C-R, Neumann E. Kinetic calibration of the calcium indicator arsenazo III. I. Stopped-flow spectroscopy. Biochimica et Biophysica Acta (BBA) - Biomembranes. 1988;938(3):456-460

Zur Berichtigung einiger der auffallendsten Unrichtigkeiten in der zu Leipzig [bei Wolfgang Gerhard] 1860 erschienen Broschüre: "Zur Emancipationsfrage des russischen Volkes ; Die Zustände des freien Bauernstandes in Kurland ; Von einem Patrioten ; [Seinem grossen Vaterlande in Liebe gewidmet]"

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