Budding of Polyps
The process of budding is completely different in scyphozoa and hydrozoa. In hydrozoa the tip of the bud develops to form the head of the polyp whereas in (many) scyphozoa the tip develops to become the foot. These differences permit further insights into the pattern forming system. 

Most hydrozoan develop colonies, that means the newly formed polyps do not detach from the parent animal. In Hydra however all buds separate. We are investigating the control of this bud separation , especially the role of signaltransduction pathways involved in this process. Keywords: PKC, TPA, calcium, lithium, diacylglycerole, staurosporine, cantharidin, chelerythrine.

Metamorphosis
In Hydractinia echinata we are investigating the processes involved in metamorphosis. Several very different (endogenous and non-endogenous) substances induce the metamorphosis   from a larvae to a polyp. Some other endogenous substances like the neurotransmitter serotonin are necessary for the induction of metamorphosis, whereas other endogenous substances are acting antagonistically by stabilising the larval state. N-methylpicolinicacid, N-methylnicotinicacid, and N-trimethylglycin belong to these substances. They influence transmethylation and the synthesis of polyamines (cf. metamorphosis of scyphozoa ).

Formation of Medusae
The formation of medusa is very different in hydrozoa and scyphozoa. In hydrozoa, medusae develop from lateral buds while in scyphzoa the head of the polyp transforms into a medusa (strobilation). We are investigating the formation of medusae and its mechanisms of control in Thecocodium quadratum and in Aurelia aurita.

Formation of colonies
Many hydrozoa show a distinct form of polyp polymorphism (differently developed polyps). Colonies from Thecocodium quadratum develop two types of polyps. One type can only catch the prey but cannot feed it, while the other one cannot catch but only feed the prey. We have investigated how an efficient distribution of these two types is reached within a colony. 

In Hydractinia echinata we are looking for how the polyps of one colony keep their distance from each other. For a long time it has been postulated that polyps supply the stolons with a substance which inhibits the formation of polyps. We found an endogenous substance (N-methylpicolinicacid) that when applied is able to enlarge the distance between the polyps and on the other hand, through inhibition of the assumed effect of this substance (transmethylation) to reduce the distances.

Thecate hydrozoa have a hydrocaulus (branched sprout with polyps) which is - compared to their athecate relatives - far more complex. It is covered with a strong perisarc consisting mostly of chitin. Due to the solid texture of the perisarc the colonies do not grow in an intercalar manner, but only terminally. Therewith the pattern of the (abundant structured) perisarc is determined by the pattern of the terminal tissue. The structure of a colony, especially of the hydrocauli, is a spatial record of the temporally change of the activity of the terminal tissue. This investigation is carried out in co-operation with Dr. Igor Kossewitch (State University of Moscow) in Gonothyrea loveni, Laomedea flexuosa, and  Obelia longissima, Dynamena pumila.

Cellbiology
In Hydra it is possible to dispense the animal into single cells. The cells can be aggregated and later on develop into normally shaped animals. Hydra tissue consists of two different cell layers, the ecto- and the entoderm. It is possible to separate those two cell layers and assemble them from different animals. Furthermore one can selectively delete the interstitial cells by incubating the animals with various substances. The so called epithelial Hydra have neither i-cells nor their derivatives for example nerve cells. In those animals the interstitial cells can be reintroduced (for example with i-cells of mutants). The various cell types are easily to distinguish. We are interested in the control of formation of epithelial cells and nerve cells and in the role these cells play in the control of pattern formation. Cell Biology .

Models of pattern formation
For many decades theoretical models   concerning the control of pattern formation in hydrozoa have been developed. These model- and methodical approaches can successfully be applied to many organisms and processes. We wish to involve experimental results gained from marine hydrozoa including thecates as well as those gained from scyphozoa into the existing models of pattern formation. Our aim is to understand what the various pattern formation systems of various organisms have in common and what the differences are. Furthermore we like to get an insight into the evolution of these systems.
 

Molecular mechanisms of development
 
 
 

Embryopharmacology / Toxicology
The metamorphosis of Hydractinia echinata is used for a systematic determination of the toxicity of simple, organic substances . The results are relevant for marine ecological systems with regard to a possible contamination by mineral oil, because mineral oil contains many of the substances we tested. There is no other investigation we know of, which addresses the effects on marine organisms systematically as we did it.  We have developed a method to enable predictions about the toxicity of not yet tested substances in other organisms. 

The embryogenesis of Brachydanio rerio is used as a tool to study the toxicity of substances in a chordate. Our investigations show that the relative extent of the effect on various organs is characteristic of a certain class of substances. Our results are (to a limited extent) applicable to other organisms and hence they are not only theoretically significant. We tested a.o. retinoids and valproicacid (anti-epileptic drug) and some of their derivatives. These substances are known to cause malformations in human embryos.