One of the most fascinating leaps in evolution is the transition from unicellular to multicellular organisms. How individual free living cells joined forces to create more complex multicellular organisms is still not well understood. For metazoans, this transition is thought to have occurred through a colonial intermediate that was composed of cells similar tochoanoflagellates。In an article published today inGenome Biology,Faircloughet al.use choanoflagellates to gain insight into this evolutionary transition.

Choanoflagellates are free-living unicellular organisms and are the closest living relatives of metazoans. The similarity between these organisms and the proposed ancestor of metazoans has made them attractive to scientists interested in studying this evolutionary shift. Indeed,a previous study of the genome of one choanoflagellate,Monosiga brevicollis, has already provided insight into the likely genetic composition of the metazoan ancestor.

In order to gain further insight into the makeup of the metazoan ancestor as well as the evolution of multicellularity, Faircloughet al.sequenced the genome ofSalpingoeca rosetta,another choanoflagellate, which is included in thearticle published inGenome Biologytoday。In this study, the authors compare theS.rosettagenome with the genomes of metazoans and metazoan outgroups including that of the choanoflagellateM.brevicollis。该分析加强了从研究的研究M.brevicollis, such as the finding that the evolution of tyrosine kinases occurred prior to the origin of metazoans, as well as increasing the number of metazoan genes inferred to have been present before the evolution of animals.

该分析还表明，虽然Choanofagellates和Metazoans的最后一个共同祖先具有一个富基因的基因组，该基因组已经包含许多已知的基因来调节动物的发育，但它也经历了明显的基因丧失和增益，在后代的演变之前。

In contrast toM.brevicollis, which is strictly unicellular, S.rosettahas both unicellular and colonial life stages, and the rosette shaped colonies produced by these individuals evoke the hypothesized colonial intermediate. Interestingly,previous researchhas shown that these colonies form through cell division, rather than through aggregation.

The existence of both single-and multicellular life stages inS.rosettahas allowed Faircloughet al.to identify genes potentially important in the regulation of the transition from unicellular to multicellular forms, through profiling transcriptional changes that occur in these different life stages. This analysis has illuminated several metazoan genes that may have been important in the evolution of multicellularity, such as theseptins。

This analysis has provided a greater understanding of our distant ancestor and helped shed more light on animal evolution, and in particular the evolution of multicellularity.