Evolutionary discovery to rewrite textbooks

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Scientists at the University of Queensland have improved the centuries-old understanding of biologists of the evolutionary history of animals.

Using a new technology to study the development of multicellular animals, their findings revealed a startling truth.

Professor Bernie Degnan said the results contradicted years of tradition.

"We found that the first multicellular animals probably did not look like modern sponge cells, but rather a collection of convertible cells," said Professor Degnan.

"The great-great-great grandmother of all the cells of the animal kingdom, so to speak, was probably quite like a stem cell.

"This is somewhat intuitive because, compared to plants and fungi, animals have many more cell types, used in very different ways – from neurons to muscles – and cellular flexibility has been essential to evolution. from the beginning. "

The results refute a long-standing idea: these multicellular animals evolved from a monocellular ancestor resembling a modern sponge cell known as choanocyte.

"The major transitions are scattered throughout the history of evolution, including the passage from a world of microscopic single cells to a world of multicellular animals," said Professor Degnan. .

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"Multicellularity has become an incredible complexity, creating the animal, plant, fungal and seaweed kingdoms we see today.

"These large organisms differ from others over 99% of the biodiversity that we only see under a microscope."

The team mapped individual cells, sequencing all expressed genes, allowing researchers to compare similar cell types over time.

Prof. Sandie Degnan, Senior Professor and Senior Author, stated that this meant that they could discover the evolutionary history of individual cell types by looking for the "signatures" of each type.

"For decades, biologists have felt that the existing theory was an obvious one, as cancellous choanocytes look so much like unicellular choanoflagellates – the organism considered to be the closest living relative of animals," she said. .

"But their transcriptome signatures just do not fit, which means that they are not the building blocks of animal life that we initially thought.

"This technology has only been used for a few years, but it finally allowed us to answer a secular question, discovering something completely contrary to what anyone else had proposed."

"We are taking a fundamental theory of the biology of evolution and turning it over," she said.

"We now have the opportunity to re-imagine the steps that gave rise to the first animals, the underlying rules that turned individual cells into a multicellular animal life."

Professor Degnan said he hoped the revelation would help us understand our own state and understanding of our own stem cells and cancer.

The study was published in Nature.