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The unicellular ancestors of animals, more complex than previously thought

An international project led by the Instituto de Biología Evolutiva (CSIC-UPF) has obtained the amoeba Capsaspora owczarzaki genome. The main striking result is that the unicellular ancestor of animals was very complex: it had more genes involved in multicellular functions than previously assumed and many of these genes play important roles in multicellulars organisms.

 Capsaspora is one of the few unicellular organisms filogenetically related to animals (Metazoa). Scientists have found out that it has more genes involved in multicellular functions than previously assumed and many of these genes can be also found in animals. Image: Multicellgenome Lab.

Capsaspora owczarzaki is a peculiar organism. It looks like an amoeba with filopodia, a kind of extensions which it uses to move. It is a symbiont of a mollusc, the tropical fresh-water snail Biomphalaria glabrata, and the only possible way of finding Capsaspora in nature is inside this snail’s body.

Capsaspora is also one of the few unicellular organisms filogenetically related to animals (Metazoa). Therefore, it can help scientists to explain how, in life evolution, unicellular organisms became multicellular.

An international project led by the Instituto de Biología Evolutiva (CSIC-UPF) has obtained the Capsaspora owczarzaki genome. The CSIC and ICREA scientist Iñaki Ruiz-Trillo is its main author, and it was published recently at Nature Communications.

The main striking result is that this close unicellular relative of animals is genetically very complex: it has more genes involved in multicellular functions than previously assumed and many of these genes can be also found in multicellular organisms. Therefore, scientists infer that unicellular ancestors of animals must have had a similar complexity. 

“It has been always said that when unicellular organisms became multicellular, many new genes appeared.”, says Ruiz Trillo, who is also associated teacher at the Barcelona University. “We have seen that not so many new genes appeared and that the ones that already existed were co-adapted, that is they transformed their functions to work within a multicellular organism”.

In Capsaspora genome scientists have found genes that are shared by animals and that are involved in functions such as cell communication, cell adhesion and differentiation of cells. Scientists do not know yet what function perform these genes in Capsaspora although, most likely they are performing something different, as Capsaspora is an unicellular organism.

Capsaspora owczarzaki belongs to the Filasterea, a family of unicellular organisms from which only two species are known: Capsaspora and Ministeria vibrans. The relationship of Filastarea with animals comes from thousands of millions of years ago, when at some point their evolutive lines diverged. (See graphic below)

Evolution of the eukaryotes, organism whose cells contain a nucleus. Animals (Metazoa), choanoflagellates and Filasterea have a a common root.

The other unicellular organisms related to animals are choanoflagellates. They are thought to be nearer relatives although, as Ruiz-Trillo points out, “ the evolutive divergence between filastereans, choanoflagellates and animals is not well known and there are not credible datations”.

Recently the genome of two chaonoflagellates (Monosiga brevicollis and Salpingoeca rosetta) were obtained.

The work has counted on the participation of scientists at the Genomic Regulation Center (Barcelona, Spain), the Broad Institute of Harvard and the Massachussets Institute of Technology (EUA), the Dalhousie University (Canada),  the Salk Institute for Biological Studies (EUA), the University of Huddersfield (UKE), the CNRS Institut Jacques Monod (France), and the University of Montreal (Canada).

 

Hiroshi Suga, Zehua Chen, Alex de Mendoza, Arnau Sebé-Pedrós, Matthew W. Brown, Eric Kramer, Martin Carr, Pierre Kerner, Michel Vervoort, Núria Sánchez-Pons, Guifré Torruella, Romain Derelle, Gerard Manning, B. Franz. Lang, Carsten Russ, Brian J. Haas, Andrew J. Roger, Chad Nusbaum & Iñaki Ruiz-Trillo. The Capsaspora genome reveals a complex unicellular prehistory of animals. http://www.nature.com/ncomms/2013/130814/ncomms3325/full/ncomms3325.html