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Amoeba gives clues to animal origins: single-celled life had molecular tools for going multicellular.

Scaling up from one cell to many may have been a small step rather than a giant leap for early life. A single-celled organism closely related to animals controls its life cycle using a molecular toolkit much like the one animals use to give their cells different roles, scientists report online October 13 in Developmental Cell.

"Animals are regarded as this very special branch, as in, there had to be so many innovations to be an animal," says David Booth, a biologist at the University of California, Berkeley. But this research shows "a lot of the machinery was there millions of years before animals evolved."

Multicellular organisms send messages between their cells and direct the cells to particular roles. The Capsaspora owczarzaki amoeba uses many of the same tricks to switch its single-celled body between different life stages. The earliest animals were probably "recycling mechanisms that were already present before," says Ifiaki Ruiz-Trillo of the Institute of Evolutionary Biology in Barcelona.

C. owczarzaki has three life stages, acting independently in some stages and aggregating with other amoebas in others. Ruiz-Trillo and colleagues analyzed C. owczarzaki's proteome--its complete set of proteins--during each life stage.

The amoeba made different amounts of proteins in each stage, suggesting that it was responding to new demands. It also shifted the way its proteins behaved.

Proteins can change behavior by grabbing on to a molecular fragment called a phosphate ion. The phosphate ion's effect depends on where it sticks to the protein and whether other phosphate ions are stuck on nearby. C. owczarzaki showed differences in the pattern of these add-ons between its life stages. In animals, proteins in different organs in the same individual show similar modifications.

The researchers also found changes in the molecules that control the protein modification process. Certain enzymes in a cell act like molecular concierges, helping phosphate ions latch on to proteins. The enzyme often determines where the ion sticks--and thus its effect. For instance, enzymes called tyrosine kinases often guide modifications that help send messages between cells. Those enzymes aren't thought to be widely used by single-celled species, says study coauthor Eduard Sabido of the Centre for Genomic Regulation in Barcelona. But C. owczarzaki uses these enzymes across its life stages, generating them in different quantities depending on the stage.

The shared molecular mechanisms suggest that the unicellular common ancestor of animals and C. owczarzaki probably used these same tricks, too, paving the way for multicellular life.

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Title Annotation:GENES & CELLS; Capsaspora owczarzaki
Author:Hamers, Laurel
Publication:Science News
Geographic Code:1USA
Date:Nov 12, 2016
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