MMEMA

Molecular mechanisms for the evolution of multicellularity in animals

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 Obiettivo del progetto (Objective)

'The evolution of multicellular animals (metazoans) from a unicellular ancestor is one of the most significant leaps in the history of life. However, little is known about the mechanisms that enabled it. Upon the acquisition of multicellularity, many molecular level innovations should have occurred, especially in the systems responsible for cell adhesion, differentiation, and cell-cell communication. Investigation of a group of protists (unicellular or colonial eukaryotes) that is closely related to metazoans should provide deep insights into molecular mechanisms for this event. Among such protists, however, only unicellular choanoflagellates have been extensively studied so far. This project aims to fill this missing piece by applying comparative genomics and molecular biological approaches to Codonosiga botrytis, a colonial choanoflagellate and two additional protists Sphaeroforma arctica and Capsaspora owczarzaki, which were recently shown to be closely related to metazoans, like choanoflagellates. To this aim, 1) the complete genome sequences of Sphaeroforma and Capsaspora, which will be exclusively available in the host institute, will be analyzed and compared to those of metazoans, in order to identify the candidate genes that were relevant to the evolution of multicellularity. Then 2) the difference in the expression profiles between the colonial and unicellular stages of Sphaeroforma and Codonosiga will be studied to identify genes responsible for forming the colony, which might represent the ‘ancestral form’ of multicellularity in metazoans. Finally, 3) molecular biological methods will be developed and applied to these protists, and functions of the candidate genes identified in 1) and 2) will be analyzed. This should elucidate the functional ‘innovations’ that enabled the evolution of multicellularity. These data will have a major impact to a wide range of research fields, especially to the ‘evo-devo’, microbiology, and molecular evolution communities.'

Introduzione (Teaser)

Research into the genomics of tyrosine kinases has shed more light on the evolutionary development of the single cell to the complexity of the multicellular animal and plant.

Descrizione progetto (Article)

Division of labour is evolution's answer to complexity with efficiency in the organism. A single-celled organism has to do all its functions in one cell. At a more complex multicellular level however, there have to be different cells to do the various jobs. The human body has more than 100 trillion cells! At the same time, there must be communication between cells and signal molecules such as the tyrosine kinases (TKs) that cause changes in target cells.

Comparing the genes of multicellular animals, metazoans, with ancestral unicellular forms may well reveal the genetic mechanisms behind this evolutionary coup. The 'Molecular mechanisms for the evolution of multicellularity in animals' (MMEMA) project studied gene families that steer multicellular functions. Overall, MMEMA were able to compare the relevant gene functions before and after the multicellular state evolved.

Sphaeroforma arctica (S. arctica) and Capsaspora owczarzaki (C. owczarzaki) were the two marine unicellular organisms, protists, chosen as they are closely related to modern metazoans. The approach was to study genomic differences between the colonial and unicellular forms of these protists to identify genes responsible for forming the colony. In a colony, some cells actually differ from each other and are slightly differentiated. There are also specialised reproductive cells within the colony.

MMEMA scientists analysed the whole genome of C. owczarzki and isolated more than 100 TKs. Together with analysis of other established genomes from other research, they concluded that cytoplasmic TKs had been established well before multicellularity. Receptor TKs that play a major role in cell differentiation and migration, however, had independently diversified in each metazoan.

project researchers were also able to film the transformation of a close relative of C. owczarzaki, C. fragrantissima, using DNA constructs. Time lapse photography recorded synchronised nuclear division in a structure called a syncytium. This functions as a single coordinated unit composed of multiple cells linked structurally and functionally.

MMEMA research successfully created a basis for investigation of the role of genetic function in evolutionary progress. The elucidation of the function of these critical genes will hopefully be able to shed light on cell differentiation and its malfunction leading to diseases like cancer.