Water shortage turns bears into "tons"
Proteins play an important role in cell protectionRead out
Even in extreme drought, tardigrades can survive for a long time. They curl up into a "barrel" and only become active again when there is enough water. Scientists in Tübingen have now found out that proteins produced under stress conditions protect the cells.
Small and frugal
Tardigrades are microscopic and frugal creatures. They have conquered many niches worldwide and live, for example, in the deep sea, in the Himalayas or in sand dunes. Often they are found in the water film that surrounds mosses or lichens. The tardigrades turn out to be particularly tough guys when the water around them becomes scarce.
While in most other organisms the cells are irretrievably damaged in extreme drought, and the organism finally dies, tardigrades endure such hardships for a long time. They collide when dehydrated in a cyst and can be easily activated again when water is added. Tübingen scientists Ralph O. Schill, Prof. Heinz-Rüdiger Köhler and Günther Steinbrück investigate at the molecular level which processes take place in the cells of the tardigrades. They have discovered that some proteins produced under stress conditions could play a crucial role in cell protection.
Water bears under the microscope
The idea of calling the traditional multi-cell heads, fuselages and four pairs of legs water bears is probably only possible with the greatly enlarged view under the microscope. Because even the largest species of tardigrades are at most one and a half millimeters in size. Its silhouette is most similar in shape to a gummy bear. Ralph Schill has studied more closely the endemic, widespread species Milnesium tardigradum, which like many other tardigrades has the ability to cryptobiosis.
If the animal dries out, all metabolic activities are suspended, the water content decreases to a few percent and the water bear assumes a Tönnchenform. In this form, the tardigrades can survive very long hostile conditions such as high energy radiation, organic solvents, short high temperatures and long very low temperatures of minus 270 degrees, near absolute zero. If you add water again, the Tönnchen transform within minutes in metabolically active animals. display
But what must happen in the case of cryptobiosis in detail, is largely in the dark. The Tübingen biologists speculated that the formation of so-called heat-shock proteins is stimulated during dehydration, similar to other organisms that are stressed. Such proteins have been found in many plant species, including the resurrection plant, which, like the tardigrades, can survive severe dehydration in a dry state.
Heat shock proteins
However, Ralph Schill was unable to directly study the proteins in the cells of the small animals, because the small animals produce only tiny amounts. The blueprint of the proteins is codified in the genetic material DNA. In fact, when comparing the DNA of the bearded animal with DNA sequences of many other animals, three genes were found in a database that are known from animals other than heat shock proteins of the Hsp 70 group.
But did the three forms of heat shock genes actually have something to do with the survival of the broom animals in extreme drought conditions? Ralph Schill has now used a method that allows researchers to measure the activity of selected genes indirectly via a fluorescence signal. The transition from an active bear animal to the state of cryptobiosis showed that Form 1 of the three heat shock genes was less frequently read, whereas Form 2 was much more common than before. With the addition of water, the conditions reversed again and Form 1 in turn came to the fore. Form 3 could be observed less at cryptobiosis but at very high temperatures.
The researchers conclude that all three heat shock genes are actually activated in the plant, especially in stress situations, and that at least some of them also play a role in the survival of dehydration. But not all riddles have long since been solved. It remains to be determined how the cell components are protected in the event of a lack of water. What the little animals playfully foster every day for us to dry cells and at the same time preserve their vitality could in the future have a not insignificant significance in the life sciences and medicine.
Their findings have now been published in the Journal of Experimental Biology.
(idw - Eberhard-Karls-Universit t T bingen, 20.04.2004 - DLO)