Champion of regeneration, the freshwater polyp Hydra² is capable of reforming a complete individual from any fragment of its body. It is even able to remain alive when all its neurons have disappeared. Researcher the University of Geneva (UNIGE), Switzerland, have discovered how: cells of the epithelial type modify their genetic³ program by overexpressing a series of genes⁴, among which some are involved in diverse nervous functions. Studying Hydra cellular⁵ plasticity may thus influence research in the context of neurodegenerative diseases. The results are published in Philosophical⁶ Transactions of the Royal Society. The freshwater Hydra is endowed with an extraordinary power of regeneration, discovered by the Swiss naturalist⁷ Abraham Trembley more than 250 years ago. The group of Brigitte Galliot, professor at the Department of Genetics and Evolution of the Faculty⁸ of Science of UNIGE, has studied the stem cells functioning and cellular plasticity of the polyp: &laquoits nervous system regulates in particular contraction⁹ bursts, feeding behavior, moving or swimming. If the stem cells responsible for its renewal¹⁰ are depleted¹¹, the Hydra can still develop, even when all its neurons have disappeared. We wanted to understand how this is possible.

 

 

The researchers compared gene¹ expression at various positions along the body axis¹² in polyps devoid¹³ or not of their nervous stem cells. They observed a modification¹⁴ of the genetic program in animals depleted of these cells: &laquowe identified 25 overexpressed genes in epithelial cells, the cells forming the Hydra's coating tissues. Some of these genes are involved in diverse nervous functions, such as neurogenesis or neurotransmission», says Yvan Wenger, co-first author of the article. 

 

&laquoEpithelial cells do not possess typical neuronal functions. However, Hydra's loss of neurogenesis induces epithelial cells to modify their genetic program accordingly, indicating that they are ready to assume some of these functions. These "naturally" genetically¹⁵ modified epithelial cells are thus likely to enhance their sensitivity and response to environmental signals, to partially¹⁶ compensate¹⁷ for the lack of nervous system», explains Wanda Buzgariu, co-first author of the article. The detail of these new functions remains¹⁸ to be discovered, as well as how epithelial cells proceed to overexpress these genes and thus adapt their genetic program.

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