In Search of Stem Cells in Immortal Lower Animals
Some lower animals are effectively immortal, in that their risk of mortality doesn't appear to increase over time. This has been demonstrated for hydra, and some other marine species have an analogous, highly regenerative biology, such as a few jellyfish and the sea anemone species noted here. Notably, none of these animals have a sophisticated nervous system and brain. The evolution of neural tissue that can store complex data appears incompatible with a lack of degenerative aging built on constant, highly proficient regeneration and replacement of all portions of the body as needed.
While humans and most vertebrates can only regenerate parts of certain organs or limbs, other animal groups have far stronger regeneration mechanisms. This ability is made possible by pluripotent or multipotent stem cells, which can form (differentiate) almost all cell types of the body. The sea anemone Nematostella vectensis is also highly regenerative: it can reproduce asexually by budding and also shows no signs of ageing, which makes it an interesting subject for stem cell research. However, researchers have not yet been able to identify any stem cells in these animals.
"By combining single-cell gene expression analyses and transgenesis, we have now been able to identify a large population of cells in the sea anemone that form differentiated cells such as nerve cells and glandular cells and are therefore candidates for multipotent stem cells."
These potential stem cells express the evolutionarily highly conserved genes nanos and piwi, which enable the development of germ cells in all animals, including humans. By specifically mutating the nanos2 gene using the CRISPR gene scissors, the scientists were also able to prove that the gene is necessary for the formation of germ cells in sea anemones. It has also been shown in other animals that this gene is essential for the production of gametes. This proves that this gene function emerged around 600 million years ago and has been preserved to this day. In future studies, researchers now want to investigate which special properties of the sea anemone's stem cells are responsible for its potential immortality.