Abstract

The emergence of multicellular animals or metazoans from their single-celled ancestors is one of the most important evolutionary transitions in the history of life. However, little is known about how this transition took place. Thus, a multi-taxon genome-sequencing initiative, named UNICORN , was launched with the aim to gain insights into metazoan origins. Recent genome data from the UNICORN project has identified a rich genetic repertoire of “multicellular” genes in unicellular relatives of metazoans. For example, the amoeba Capsaspora owczarzaki, a close relative to metazoans, encodes both cadherins and integrins, which are absent in plants and fungi and which were thought to be metazoan-specific. Moreover, the genome of Capsaspora encodes transcription factors that are key to animal development, such as T-box genes or Runx, as well as dozens of protein tyrosine kinases. These findings challenge previous views in which the origin of metazoan multicellularity was thought to be accompanied by the invention and diversification of genes families specifically involved in multicellularity. These findings open new questions, such as the role those “multicellular” genes are playing in an unicellular context, and how were they co-adapted into the new (multicellular) functions. Current and future efforts to answer those questions will be discussed.