Interferenzmikroskopische Untersuchungen an Medulloblastom- und Glioblastomzellen

Summary The dry mass per unit area (g/µ²) for nucleus and cytoplasma was determinated by interference microscope from 1043 glioblastoma cells of 5 various glioblastomas and from 439 medulloblastoma cells of 4 various medulloblastomas. The values obtained from the glioblastoma cells are significantly higher than the values of medulloblastoma cells.

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Mit dankenswerter Unterstützung der Deutschen Forschungs gemeinschaft.     

d-Aminosäurehaltige Analoga des Eledoisins

Summary The synthesis of several C-terminal eledoisin heptapeptide analogues, containing 1–5d-amino acids, is described and the biological activities are discussed.

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Über Peptidsynthesen XXXI. 4. Mitt. über Eledoisin und Eledoisin-Analoga. 3. Mitt. über Eledoisin und Eledoisin-Analoga:K. Lübke undE. Schröder, Liebigs Ann., im Druck.

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Auszugsweise vorgetragen auf dem VII. Europäischen Peptidsymposium, September 1964 in Budapest.     

Relation between the glycogen content of the liver and liver weight,and its meaning for enzymology

Zusammenfassung Schwankungen des Glykogengehalts verursachen sehr schnelle Veränderungen des Lebergewichtes und daher auch solche des prozentualne Proteingehalts der Leber. Enzymaktivität sollte deshalb pro Körpergewicht und nicht pro Lebergewicht ausgedrückt werden, wie dies oft geschieht.

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Acknowledgments. The authors wish to express their gratitude ProfessorA. de Minjer for his support, to ProfessorL. W. J. Holleman, ProfessorJ. W. Koten and ProfessorH. Schimassek for helpful suggestions and to Mrs.L. C. Freelink-vander Velden for technical assistance.     

Identification of a catecholamine in the skin of the toad,Xenopus laevis,and the relation to the physiological melanophore reaction

Zusammenfassung Mit Hilfe chemischer und histochemischer Technik gelingt in der Haut vonXenopus laevis der Nachweis eines dopamingefüllten Reservoirs. Das Catecholamin ist mit der physiologischen Melanophorenreaktion verbunden.

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The authors are indebted to Prof. J. C. van deKamer for his encouragement and interest in these studies.     

T-cell receptor triggering is critically dependent on the dimensions of its peptide-MHC ligand

The binding of a T-cell antigen receptor (TCR) to peptide antigen presented by major histocompatibility antigens (pMHC) on antigen-presenting cells (APCs) is a central event in adaptive immune responses. The mechanism by which TCR-pMHC ligation initiates signalling, a process termed TCR triggering, remains controversial. It has been proposed that TCR triggering is promoted by segregation at the T cell-APC interface of cell-surface molecules with small ectodomains (such as TCR-pMHC and accessory receptors) from molecules with large ectodomains (such as the receptor protein tyrosine phosphatases CD45 and CD148). Here we show that increasing the dimensions of the TCR-pMHC interaction by elongating the pMHC ectodomain greatly reduces TCR triggering without affecting TCR-pMHC ligation. A similar dependence on receptor-ligand complex dimensions was observed with artificial TCR-ligand systems that span the same dimensions as the TCR-pMHC complex. Interfaces between T cells and APCs expressing elongated pMHC showed an increased intermembrane separation distance and less depletion of CD45. These results show the importance of the small size of the TCR-pMHC complex and support a role for size-based segregation of cell-surface molecules in TCR triggering.     

The phylogenetic position of the 'giant deer' Megaloceros giganteus

The giant deer, or 'Irish elk', has featured extensively in debates on adaptation, sexual selection, and extinction. Its huge antlers--the largest of any deer species, living or extinct--formed a focus of much past work. Yet the phylogenetic position of the giant deer has remained an enigma. On the basis of its flattened antlers, the species was previously regarded as closely related to the living fallow deer. Recent morphological studies, however, have challenged that view and placed the giant deer closer to the living red deer or wapiti. Here we present a new phylogenetic analysis encompassing morphological and DNA sequence evidence, and find that both sets of data independently support a sister-group relationship of giant and fallow deer. Our results include the successful extraction and sequencing of DNA from this extinct species, and highlight the value of a joint molecular and morphological approach.     

Gene flow maintains a large genetic difference in clutch size at a small spatial scale

Understanding the capacity of natural populations to adapt to their local environment is a central topic in evolutionary biology. Phenotypic differences between populations may have a genetic basis, but showing that they reflect different adaptive optima requires the quantification of both gene flow and selection. Good empirical data are rare. Using data on a spatially structured island population of great tits (Parus major), we show here that a persistent difference in mean clutch size between two subpopulations only a few kilometres apart has a major genetic component. We also show that immigrants from outside the island carry genes for large clutches. But gene flow into one subpopulation is low, as a result of a low immigration rate together with strong selection against immigrant genes. This has allowed for adaptation to the island environment and the maintenance of small clutches. In the other area, however, higher gene flow prevents local adaptation and maintains larger clutches. We show that the observed small-scale genetic difference in clutch size is not due to divergent selection on the island, but to different levels of gene flow from outside the island. Our findings illustrate the large effect of immigration on the evolution of local adaptations and on genetic population structure.