Yearbook 2004

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When substances are produced in one cell, yet required in another, they have to travel long distances in a tissue. So far, common science has not been able to adequately explain this process. Now, MPI-CBG researchers of the groups of Suzanne Eaton and Christoph Thiele have discovered so-called argosomes: Like trucks, they are able to pick up proteins and transport them from one cell to the other within a tissue. Wnt and Hedgehog family proteins are secreted signalling molecules (morphogens) that act at both long and short range to control growth and patterning during development. Both proteins are covalently modified by lipid, and the mechanism by which such hydrophobic molecules might spread over long distances is unknown. The Dresden labs could show that Wingless, Hedgehog and gpi-linked proteins copurify with lipoprotein particles, and co-localize with them in the developing wing epithelium of Drosophila. In larvae with reduced lipoprotein levels, Hedgehog accumulates near its site of production, and fails to signal over its normal range. Similarly, the range of Wingless signalling is narrowed. Thus, a novel function for lipoprotein particles has been characterised: they act as vehicles for the movement of lipid-linked morphogens and gpi-linked proteins. more
Light microscopy has continually played a key role in science, but diffraction has limited the imaging of details that are smaller than about half the wavelength of light. For the important contrast mode of fluorescence, which is crucial to modern cell and molecular biology, the diffraction barrier has now been broken. In spite of relying on focused visible light, stimulated emission depletion (STED) microscopy is not limited by diffraction. To date, current schemes of STED-microscopy have delivered 50 nm (1/12 of the wavelength) resolution on cell membranes. more
Animals are made of two major cell types, somatic cells that are responsible for the development and survival of the organism (e.g. muscle cells, cells in the nervous system etc.) and germ cells that are responsible for the generation of a new organism in the next generation by forming sperm and eggs. Scientists at the MPI in Göttingen are studying the development of germ cells in zebrafish, a vertebrate model organism that offers numerous advantages for such studies. Importantly, zebrafish embryos develop outside the body of the mother and are translucent allowing us to easily observe the germ cells within the live animal. Moreover, in studying the development of the cells we can use a large number of genetic techniques such as reducing the level of specific proteins, expression of different genes in different positions in the embryo etc. The research focus of our group is the understanding of the molecular basis for early germ cell development and behavior as well as studying the interaction between somatic and germ cells. To this end we analyze the mechanisms that are responsible for the segregation of the somatic and germ cell populations and the mechanisms responsible for the migration of the cells towards the gonad, the organ in which they generate sperm and eggs. Using mutations affecting the development of somatic cells we can determine whether the somatic cells provide the germ cells with signals important for their development and conversely, we analyze the development of somatic cells in which germ cell development is blocked. more

Anatomy of a mantle plume

Max Planck Institute for Chemistry Hofmann, Albrecht W.; Sobolev, Alexander; Abouchami, Wafa; Galer, Stephen J.
Researchers of the Geochemistry Department developed a new model of melt production in a mantle plume to explain the enormous magma production of Hawaiian volcanoes. They also showed that the Hawaiian mantle plume is compositionally not purely concentric, but consists of two isotopically different halves. more

Synthesis of Polymeric Nitrogen

Max Planck Institute for Chemistry Eremets, Mikhail I.; Gavriliuk, Alexander G.; Trojan, Ivan A.; Boehler, Reinhard
We report on an allotropic form of nitrogen where the atoms are connected with single covalent bonds, similar to carbon atoms in diamond. Nitrogen under ambient conditions consists of molecules where two atoms are strongly triple-bonded. The new substance was synthesized directly from molecular nitrogen at temperatures above 2,000 K and pressure above 110 GPa (ca. 1.1 million atmospheres) using a laser-heated diamond cell. From X-ray and Raman scattering we have identified this as the long-sought-after polymeric nitrogen with the theoretically predicted cubic gauche structure (cg-N). This cubic phase has not been observed previously in any element. The new phase is a stiff substance with bulk modulus ≥300 GPa, characteristic of strong covalent solids. This polymeric nitrogen is metastable, and contrasts with previously reported amorphous non-molecular nitrogen, which most likely is a mixture of small clusters of non-molecular phases. The cg-N represents a new class of single-bonded nitrogen materials with unique properties such as energy capacity: more than 5 times that of the energetically most powerful materials. more
Of the language centres of the human brain, Broca’s region in the left frontal lobe is arguably the most famous. While this brain region was originally thought to be responsible for language production, research during the last decades has focused increasingly on its possible role in language comprehension. In particular, Broca’s region is activated more strongly during the comprehension of sentences in which the object precedes the subject. Researchers at the Max Planck Institute for Human Cognitive and Brain Sciences have recently proposed a new explanation for such findings, which assumes that Broca’s region plays a crucial role in the sequential ordering of different linguistic information types. more
Cognitive psychology usually examines performance of subjects in different experimental tasks. However, there is no consensus as regards how a “task” can be defined. In many experiments the requirement to categorize a stimulus is equated with the term task. A study of the Max Planck Institute for Human Cognitive and Brain Sciences demonstrates that the modality of a response (e.g. verbal or manual responses) is equally important for the definition of a task. The results provide evidence that the same cognitive processes underlie switching between response modalities and switching between stimulus categories. more
What role do taxes and user fees play for public goods finance? If a public good is excludable, one can charge a user fee and exclude anybody who fails to pay the fee. If the enjoyment of the public good by an additional person entails no costs, this exclusion is inefficient. However, the inefficiency must be compared to the inefficiencies induced by other financing instruments such as income tax. Research results of the Max Planck Institute for Research on Collective Goods show that, under incomplete information about individual preferences for public goods and about labour productivity levels, an optimal incentive mechanism will make use of all available financing instruments and thereby minimize overall efficiency loss. The optimal mix of instruments satisfies a version of the “elasticities rule” of public sector pricing. more
Biomimetic systems with fine-tuned properties have many potential applications such as drug delivery systems or biosensors. In order to design such systems, one needs a detailed understanding of the underlying nanostructures and nanoprocesses. These structures are very thin and have a thickness of a few nanometers which makes them rather flexible and mobile. There is no experimental method by which one could directly image the dynamics of these structures. Therefore, it is rather appealing to use computer simulations in order to visualize these processes. A particularly powerful simulation method is provided by Dissipative Particle Dynamics which can be used to monitor supramolecular systems with a linear dimension of up to 50 nanometers over a time period of several microseconds. In this article, we discuss three examples for such systems: lipid membranes that contain several components and form different intramembrane domains; vesicles composed of diblock copolymers which could be used as drug delivery systems; and tension-induced fusion of bilayer membranes. The method of Dissipative-Particle-Dynamics can be used to optimize nanostructures and -processes in silico before one performs many costly experiments. more
Living bone is continuously remodeled via resorption and deposition of small bone packets. This remodeling process is controlled by a mechanical feedback loop, which allows bone to adapt to varying mechanical requirements. Being experimentally difficult to access, the feedback loop is intensively studied using computer modeling. In the simulation it is possible to discriminate between changes in the bone structure due to either aging or disease. With a better understanding of the interrelation between the feedback loop and changes in the bone structure, there is hope that improved therapies act directly on the real reasons of bone diseases. more
For perceiving the environment our brain uses multiple sources of sensory information derived from several different modalities, including vision, touch and audition. Some sources of sensory information derived from different modalities provide information about the same object property or event. For example, the size of an object can both be seen with the eyes and felt with the hands. This is called redundant sources of sensory information. In this report we will show how such redundant sources of sensory information are used by the human brain in order to interact with the environment in a purposive fashion. Further, we describe which role prior knowledge plays concerning the statistical regularities in the world and how this can affect the process of perception. As a model for describing such somatosensory interactions we apply the Bayesian Decision Theory (BDT). more
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