Iñaki Ruiz-Trillo directs the MulticellGenome Lab at IBE and has been awarded a scientific research grant from the European Research Council (ERC). The ERC Advanced Grant has an endowment of 2.5 million euros and will finance the “MISSINGRELATIVES” project for 5 years. During this time, the researcher and his team will work to find out how the evolutionary leap from unicellular organisms to animals occurred, an innovative project in the field of evolutionary biology.

The ERC Advanced Grant is among the most prestigious and competitive funding programs in the European Union and is aimed at researchers with long scientific careers with an ambitious proposal. Of the 1,650 applicants that have applied this year, however, only 13.2% have achieved this award for scientific excellence, which not only considers the degree of innovation of the proposal but also the applicant's professional career.

Iñaki Ruiz-Trillo, Principal Investigator at IBE

“We have worked for fifteen years to find out which are our closest relatives among single-celled organisms and what genetic and molecular characteristics they share with animals. We have found four close lineages, which we would call our "relatives", and we have discovered that they have characteristics in the genome that were thought to be exclusive to animals, such as integrins, responsible for cell adhesion and the ability to form aggregates or temporary multicellular forms.” Ruiz-Trillo explains his research, which began in the postdoctoral stage.

"With this new project, however, we want to use genetic tools that are innovative, or that have improved over the years, to discover and isolate new lineages that are in a key phylogenetic position to understand the transition to animals." Adds Ruiz-Trillo.

Where did the first animal come from?

Millions of years ago, single-celled organisms such as bacteria, some algae, and fungi inhabited a planet without animals or plants, therefore, without multicellular organisms. At one point, these organisms came together to create colonies and generate synergies between them, and this collaboration became mandatory. Cells differentiated to carry out specialized tasks within the same organism, and some evolved into animals, also called metazoans.

“Although there are unicellular organisms close to animals that can do many things and seem to be 'ready' to become multicellular, the truth is that they are very different from animals. We do not know how embryonic development or cell differentiation originated, nor when. This may be because either the intermediate lineages became extinct at some point, or we haven't found them yet." Adds Iñaki Ruiz-Trillo, who in this ambitious proposal has undertaken the search for these intermediate lineages, missing links in the transition to multicellularity.

5 years to find the missing link with the latest technology in genetics

There are many unicellular organisms unknown to the scientific community and among them, there could be key lineages to understand the origin of animals. This is because these microorganisms are widely dispersed in the environment and some cannot be grown in the laboratory. In addition, no study to date has conducted an exhaustive search for single-celled organisms close to animals.

Iñaki Ruiz-Trillo and his team, however, have discovered 8 new lineages collected in water samples with Metabarcoding. A few years ago, this genetic detection technique was capable of taxonomically classifying different species of organisms in the same sample and identifying new ones, but it did not allow an exact classification or identification of living organisms.

“Thanks to the development of metabarcoding technology and the development of long-read sequencing, we will now be able to understand the phylogenetic position of these organisms much better and eventually try to isolate them.” Ruiz-Trillo points out.

With the genetic information generated with Metabarcoding, the project will develop new Fluorescent In situ Hybridization (FISH) tools to detect, for the first time, eukaryotes in vivo. This molecular technique allows the detection of specific DNA sequences and it has been possible to preserve living prokaryotes during the procedure. The detection of eukaryotes in vivo is one of the objectives of this project and would be an innovation of great impact in the study of these microorganisms.

In this way, those that are of interest could be cultivated to study the characteristics through genetic techniques to silence or overexpress genes and thus find out their functions.
"Knowing this diversity of functions, discovering new genes, or observing stable multicellular behaviors, among others, would help us to understand how the unicellular ancestor could have evolved to form the first animal." Adds Iñaki Ruiz-Trillo.

About Inaki Ruiz-Trillo

Iñaki Ruiz-Trillo is an ICREA research professor and Principal Investigator of the MulticellGenome Lab at the Institute of Evolutionary Biology (CSIC-UPF). He obtained a Ph.D. in Biology from the University of Barcelona and completed a postdoctoral fellowship at Dalhousie University (Canada). He has also conducted short-term research projects at the Joint Genome Institute at the University of Arkansas and the Kavli Institute for Theoretical Physics. Additionally, he is a member of EMBO and has been part of the editorial board of several magazines.