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Most ancient and primitive animal on earth reveals secrets about evolution

Most ancient and primitive animal on earth reveals secrets about evolution

January 2013

NPC researchers (Utrecht University) together with colleagues from the Tierärztliche Hochschule in Hannover, have for the first time measured global protein expression in Trichoplax; the most ancient and primitive animal on earth, making discoveries about the earliest stages of animal evolution. The results are published in Nature Communications.

The first animals on earth arose when single celled ancestors aggregated and started to specialize and work together as a multicellular organism. This organism now acquired its energy for living by feeding on other organisms. Cells needed to specialize and cooperate in a coordinate way and thus communicate with each other in even more complex ways than already existed.
Crucial decisions needed to be communicated about which cells acquired what function or might even have to commit suicide for the sake of the whole organism. A special network of crosslinking and interacting molecules formed an extracellular matrix to provide a structural support and hold each cell in its correct place. Also systems were needed to exactly reproduce this whole structural and functional organization of cells in the offspring of the animal.


Trichoplax adhaerens

Research in Trichoplax adhaerens of the phylum Placozoa, which is the most ancient and primitive animal still living today, does provide information on the evolution and functioning of these processes. This animal appears as a flat disk of only a few millimeters consisting of a few thousand of only five different cell types. Now protein expression encoded by more than half of all the 11.500 predicted genes present in the genome of Trichoplax was monitored.


Novel cellular information system

The main new finding concerns the evolution of a novel cellular information system more than 600 million years ago. In animal cells much information and communication is carried out by modifying proteins, adding (writing) a tag in the form of a phosphate group to tyrosine amino acids.
This tag can be read and also erased by other proteins. This new tri-partite system had so much information coding potential that it made the appearance of animal multicellularity possible. The group in Utrecht was able to detect these phospho tags in the oldest known animal and show that this invention was accompanied by a sudden burst in the frequency of phospho-tagged tyrosines in proteins.


Grazers

Another finding is related to the idea that the first animals were grazers that would move over and on top of its food which was then digested externally by uptake of the released nutrients, just like Trichoplax still does today. The researchers show that Trichoplax, which does not have a gut with associated flora acquired a gene from bacteria which made it possible to scavenge certain nutrients from it’s food.
Other findings include the detection of proteins important in processes thought to be characteristic of more complex animals. These include proteins involved in developmental signalling pathways, proteins involved in sexual reproduction, as well as putative extra cellular matrix proteins.


Publication

Deep proteome profiling of Trichoplax adhaerens reveals remarkable features at the origin of metazoan multicellularity
J.H. Ringrose, H.W.P. van den Toorn, M. Eitel, H. Post, P. Neerincx, B. Schierwater, A.F.M. Altelaar, A. J. R. Heck 
Nature Communications 2013, DOI 10.1038/ncomms2424

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