Klaus Herrmann
University of Cologne
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Featured researches published by Klaus Herrmann.
The Biological Bulletin | 2001
Igor A. Kossevitch; Klaus Herrmann; Stefan Berking
The colonies of thecate hydroids are covered with a chitinous tubelike outer skeleton, the perisarc. The perisarc shows a species-specific pattern of annuli, curvatures, and smooth parts. This pattern is exclusively formed at the growing tips at which the soft perisarc material is expelled by the underlying epithelium. Just behind the apex of the tip, this material hardens. We treated growing cultures of Laomedea flexuosa with substances we suspected would interfere with the hardening of the perisarc (l-cysteine, phenylthiourea) and those we expected would stimulate it (dopamine, N-acetyldopamine). We found that the former caused a widening of and the latter a reduction in the diameter of the perisarc tube. At the same time, the length of the structure elements changed so that the volume remained almost constant. We propose that normal development involves a spatial and temporal regulation of the hardening process. When the hardening occurs close to the apex, the diameter of the tube decreases. When it takes place farther from the apex, the innate tendency of the tip tissue to expand causes a widening of the skeleton tube. An oscillation of the position at which hardening takes place causes the formation of annuli.
Development Genes and Evolution | 1990
Stefan Berking; Klaus Herrmann
SummaryLarvae of the tunicate Ciona start metamorphosis between some hours and a few days after hatching. Several substances were found to reduce this time span, such as vital dyes [Cloney (1961) Am Zool 1:67–87; Hirani (1961) Bull Mar Biol Stn Asamushi 11:121–125], heavy-metal ions including copper [see review by Lynch (1961) Am Zool 1:59–66] and the hormone thyroxine [Patricolo et al. (1981) Cell Tissue Res 214:289–301]. This study shows that low concentrations of ammonium ions as well as the second messenger dicapryloylglycerol induce metamorphosis immediately after hatching. On the other hand, when the follicle cells are removed newly hatched Ciona remain larvae for days. Follicle cells are possibly degraded by bacteria, which thereby produce ammonia.
Development Genes and Evolution | 1994
Stephan Wacker; Klaus Herrmann; Stefan Berking
Following fertilization of eggs of Brachydanio rerio a blastodisc is formed which, by cleavage divisions and epibolic movements, gives rise to a cell cap covering the yolk. When about half of the yolk is covered by the cells, a thickening appears at the progressing margin, the embryonic shield, which gives rise to the axial organs of the future embryo. Thereby, the dorsal/ventral axis can be recognized. Our experiments show that the blastodisc is formed at the position of the micropyle, the only site where the sperm can enter the egg and oocyte. Later the head appears at this position. We show that the position of the embryonic shield on the circumference of the cell cap is influenced by gravitation. We also demonstrate that there is no correlation between the orientation of the first or second cleavage plane and the position of the embryonic shield.
Central European Journal of Biology | 2010
Stefan Berking; Klaus Herrmann
When all the cells of a tube are identical, they are unlikely to control how many of them are present in the circumference. However, when the circumference is subdivided into at least two regions of different cells, the tube diameter can be controlled via the width of these regions. We present a model and computer simulations for the formation of a tube which starts as a cone-like protrusion from a flat sheet of cells. Cells can exist in two alternative states. Cells of one state need signalling from those of the other state in order to maintain their state. Hence the cells of the two states arrange in stripes. A pattern-forming system, which defines where in this field of cells a tube will start to form, causes the stripes to become small at that very site. When four stripes originate at that point, and when the angle between the two borders of the stripes (as measured from the centre of the field) is less than 90°, the tissue is forced to protrude in the form of a cone. This model may help to understand the morphogenesis proper of buds of Cnidaria and of tubes, such as that of insect legs and the neural tube of vertebrates.
Central European Journal of Biology | 2009
Stefan Berking; Uwe Hoffmann; Mathias Schäfer; Klaus Herrmann
The fresh water polyp Hydra is noted for its ability to regenerate missing body parts. Transplantation experiments indicate that the control of regeneration includes signalling over long distances. These signals appear to include diffusible morphogens, activators and inhibitors. In order to elucidate the nature of such signals, tissue of polyps was homogenized and fractionated. The fractions were tested for their ability to hinder head regeneration. The active factor within these fractions was determined to be methionine. Both the active fractions and L-methionine were found to antagonize not only head regeneration but also foot regeneration. Budding, the asexual means of reproduction, is antagonized. L-methionine acts in micromolar concentrations while the stereoisomer D-methionine does not. L-methionine may act by providing a methyl group in transmethylation processes.
The International Journal of Developmental Biology | 2005
Stefan Berking; Nicole Czech; Melanie Gerharz; Klaus Herrmann; Uwe Hoffmann; Hartmann Raifer; Guy Sekul; Barbara Siefker; Andrea Sommerei; Fritz Vedder
Helgoland Marine Research | 2006
Stefan Berking; Klaus Herrmann
Quantitative Structure-activity Relationships | 2000
Sergiu Adrian Chicu; Klaus Herrmann; Stefan Berking
The International Journal of Developmental Biology | 2002
Stefan Berking; Marco Hesse; Klaus Herrmann
Development | 1987
Klaus Herrmann; Stefan Berking