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

On MSE-optimal crossover designs

In crossover designs, each subject receives a series of treatments one after the other. Most papers on optimal crossover designs consider an estimate which is corrected for carryover effects. We look at the estimate for direct effects of treatment, which is not corrected for carryover effects. If there are carryover effects, this estimate will be biased. We try to find a design that minimizes the mean square error, that is the sum of the squared bias and the variance. It turns out that the designs which are optimal for the corrected estimate are highly efficient for the uncorrected estimate

On MSE-optimal circular crossover designs

In crossover designs, each subject receives a series of treatments, one after the other in p consecutive periods. There is concern that the measurement of a subject at a given period might be influenced not only by the direct effect of the current treatment but also by a carryover effect of the treatment applied in the preceding period. Sometimes, the periods of a crossover design are arranged in a circular structure. Before the first period of the experiment itself, there is a run-in period, in which each subject receives the treatment it will receive again in the last period. No measurements are taken during the run-in period. We consider the estimate for direct effects of treatments which is not corrected for carryover effects. If there are carryover effects, this uncorrected estimate will be biased. In that situation, the quality of the estimate can be measured by the mean square error, the sum of the squared bias and the variance. We determine MSE-optimal designs, that is, designs for which the mean square error is as small as possible. Since the optimal design will in general depend on the size of the carryover effects, we also determine the efficiency of some designs compared to the locally optimal design. It turns out that circular neighbour-balanced designs are highly efficient

The non-obligatory role of endothelial cells in the relaxation of arterial smooth muscle by acetylcholine

The concept of Endothelium Derived Relaxing Factor (EDRF), put forward by Furchgott in the earlier 80s of the past century, implies that nitric oxide (NO) produced by NO synthase (NOS) in the endothelium in response to acetylcholine (ACh) passively diffuses to the underlying vascular smooth muscle cells (VSMC) thereby reducing vascular tension. It was thought that VSMC do not express NOS by themselves, but to the time of those studies immunohistochemical techniques were not what they are now. State-of-the-art immunohistochemistry permits nowadays to localize NOS both to the endothelium and to VSMC. However, the principal question remained unanswered, is the NO generation by VSMC physiologically relevant? We hypothesized that the destruction of the vascular wall anatomical integrity by rubbing the blood vessel intimal surface may increase vascular superoxides that, in turn, reduce NO bioactivity. To address this issue, we examined ACh-induced vasorelaxation in endothelium-deprived blood vessels under protection against oxidative stress and found that superoxide scavengers - tempol and N-acetyl-L-cysteine - restored vasodilatory responses to ACh in endothelium-deprived blood vessels without influencing the vascular wall tension in intact blood vessels. Herewith we provided the first evidence that VSMC can release NO in amounts sufficient to account for the vasorelaxatory response to ACh. In contrast to the commonly accepted concept of the obligatory role of endothelial cells in the relaxation of arterial smooth muscle, the local NO generation by VSMC can modulate vascular functions in an endothelium-independent manner

Production and Function of Serotonin in Cardiac Cells

Serotonin [5-hydroxy-tryptamine (5-HT)] exerts a number of effects in the mammalian heart: increase in heart rate, increase in force of contraction, fibrosis of cardiac valves, coronary constriction, arrhythmias and thrombosis. These effects are, in part, mediated by 5-HT-receptors, in part, directly by 5-HT action on intracellular proteins. In the beginning, 5-HT was thought to be only produced in the gut and then transported into the heart via platelets, because platelets can take up 5-HT in the gut and enter the capillaries and thus the mammalian heart. 5-HT is to a large extent metabolized in the liver and excreted via the urine. Here, we will also overview data that argue for additional pathways, namely production and degradation of 5-HT in the cells of the heart itself

Computing minimum cuts by randomized search heuristics

We study the minimum s-t-cut problem in graphs with costs on the edges in the context of evolutionary algorithms. Minimum cut problems belong to the class of basic network optimization problems that occur as crucial subproblems in many real-world optimization problems and have a variety of applications in several different areas. We prove that there exist instances of the minimum s-t-cut problem that cannot be solved by standard single-objective evolutionary algorithms in reasonable time. On the other hand, we develop a bicriteria approach based on the famous MaxFlow-MinCut Theorem that enables evolutionary algorithms to find an optimum solution in expected polynomial time

Der Einfluss organischer Düngung im Langzeitdüngungsversuch auf das Ausmaß der Wurzelinfektion mit Arbuskulärer Mykorrhiza sowie die Entwicklung des wurzelexternen Myzels bei Kartoffel (Solanum tuberosum)

In the present study, AMF root colonisation of potato plants was compared between organically and minerally fertilised field plots, which did not significantly differ in the total amount of plant available P. The AMF root colonisation was increased in response to organic fertilisation. This indicates that organic fertilisation can enhance AMF development independently from the soil P fertilisation level. Furthermore, soil grown mycelium was trapped in fungal compartments. This technique allowed the extraction and quantification of coarse and finely branched soil grown hyphae after harvest. The soil in the fungal compartments was either fertilised with low or with high amounts of mineral P. In organically fertilised field plots, the amounts of finely branched hyphae in fungal compartments filled with soil of a high P fertilisation level were much higher compared to compartments filled with low P soil. It is discussed, whether AMF isolates from organically managed field sites have a better ability to forage for locally restricted, P rich soil patches compared to AMF isolates from minerally fertilised fields