The transition from single-celled organisms to multicellular animals (metazoans) is one of the most mysterious open questions in biology. To understand the mechanisms involved in this transition it is vital to study the closest unicellular relatives of metazoans. But the analyses on these protists have been severely limited by the lack of transgenesis tools and the difficulty in culturing these simple organisms.
In this article published in Developmental Biology, the Multicellgenome lab the led by Iñaki Ruiz-Trillo at the IBE (CSIC-UPF) presents the first techniques of cell transformation and gene silencing developed in a close relative of metazoans, the ichthyosporean Creolimax fragrantissima. This organism exists both in colonial and amoebal stages. Using transgenesis, the authors here demonstrate that the colony develops from a fully-grown multinucleate syncytium, in which nuclear divisions are strictly synchronized.
They also explain that the genomes of these tiny organisms contain, unexpectedly, several key genes encoding proteins important for metazoan development and multicellularity, such as those involved in cell-cell communication, cell proliferation, cell differentiation, and tissue growth control.
It has been hypothesized that metazoan multicellular development initially occurred through successive rounds of cell division or through cell aggregation. Based on their findings, the authors point to another possible mechanism for the evolution of animal multicellularity: cellularization of a syncytium in which nuclear divisions are synchronized.
Either way, they propose C. fragrantissima as a model organism to investigate, using the transgenesis techniques they have developed, what these ‘multicellular’ genes are doing in protists. Understanding this could indeed provide novel insights into the origin of metazoan multicellularity.
Suga H, Ruiz-Trillo I. Development of ichthyosporeans sheds light on the origin of metazoan multicellularity. Dev Biol. 2013 Jan 17;