Flatworms: microRNAs provide for regeneration

How to replace planarians with lost parts

Flatworms are masters of regeneration and ideal for researchers to study stem cells and their controls. © A. Sanchez Alvarado / HHMI
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Flatworms are only a few millimeters to centimeters in size, live in the sea or in rivers and are intensively researched. The animals owe their extraordinary ability: with the help of their stem cells, a completely new, viable flatworm grows out of any separated part of the body. Now, an international research team has presented the first comprehensive catalog of small RNAs - gene controls - the Planarians. They also identified small RNAs that could play a role in regeneration and stem cell function.

The team of scientists led by Nikolaus Rajewsky from the Max Delbrück Center (MDC) Berlin-Buch presents his findings together with colleagues from the USA and Canada in the Early Edition of the journal "Proceedings of the National Academy of Sciences" (PNAS).

Previous research suggests that hundreds of genes are involved in the regeneration process of flatworms or planarians. The question is, how are these genes regulated? Scientists are therefore using the most modern techniques for the control of genes such as the small RNAs, in particular the microRNAs (miRNAs).

Unique model system

Among the thousands of planarian species, Team of researchers in Germany, Canada and the US has selected the flatworm of the species Schmidtea mediterranea. 30 percent of cells of this type consists of stem cells, making it a unique model system to study the function of stem cells.

Many of the planarian genes are similar to those of humans and many genes associated with the stem cells and the self-healing powers of planarians are conserved in humans. For this reason, the researchers hope to gain insights into the regeneration mechanisms and stem cell biology of humans from the study of planarians. display

Search for microRNAs

The MDC researchers and their colleagues in the US and Canada searched for small RNAs both in the planarians' stem cells and in their entire organism. They discovered about 60 new microRNA genes and showed that more than ten microRNAs are specifically linked to stem cell biology and therefore likely to play a role in regeneration. Some of these microRNAs are also available in humans.

The research team also found millions of so-called piRNAs. This is a recently discovered new strain of small RNA genes important for the stability of the genetic material. The researchers were able to show that piRNAs are present in large quantities in planar stem cells and function there with similar mechanisms as in mammals.

"Immortal" stem cells

Since stem cells are virtually immortal, they must keep their genetic material strictly under control. Because of this, piRNAs in the fly and the mouse quiesce jumping genes (transposons). These genes can change their location in the genome and thereby trigger mutations.

Based on their analyzes, the researchers suspect that the piRNAs in the planarian stem cells have a similar function. This should now show further research.

(idw - Max Delbr ck Center for Molecular Medicine (MDC) Berlin-Buch, 07.07.2009 - DLO)