Friday, November 25

Aquatic sponges could have clues to the origin of the brain

Made up of some 86 billion neurons, the human brain controls bodily functions – such as vision or movement – and also provides awareness and understanding; However, despite its great importance, when and how this biological machine emerged remains unknown.

It is known that the first animal brains appeared hundreds of millions of years ago and that only the most primitive animal species, such as aquatic sponges, lack it.

Now, a study published in Science claims that, paradoxically, sponges can help unravel the mystery of how neurons and brains evolved.

Neurons in the brain communicate through connections between cells (synapses) that are the core of brain function and are regulated by a series of genes.

Sponges do not have these synapses, but their genome still encodes many of the synaptic genes. But if they don’t have a brain, what is the function of these genes?

“Although it seems simple, answering this question was beyond our technological capabilities until now,” warns the group head of the European Molecular Biology Laboratory (EMBL, in its acronym in English) Detlev Arendt, co-author of the study.

To study the role of these synaptic genes in sponges, Arendt’s lab used microfluidic technologies and genomic technologies in the freshwater sponge Spongilla lacustris, techniques that allowed scientists to capture individual cells from various sponges within microfluidic droplets. and then profile the genetic activity of each cell.

“We show that certain cells in the digestive chambers of sponges activate synaptic genes. Thus, even in a primitive animal that lacks synapses, synaptic genes are active in specific parts of the body,” says Jacob Musser, a researcher in the group of Arendt and lead author of the study.

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The study details that sponges use their digestive chambers to filter food from the water and interact with microbes in the environment.

“By combining electron microscopy with synchrotron beamline X-ray imaging, we were able to visualize the impressive behavior of these cells,” explains Yannick Schwab, a researcher at EMBL in Hamburg, Germany.

Cells through the digestive chamber

The scientists captured three-dimensional snapshots of cells crawling through the digestive chamber to kill invading bacteria and sending long arms that wrap around the feeding apparatus of certain digestive cells.

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This behavior creates an interface for directed cell-cell communication, as it also occurs across synapses between neuronal cells in our brain.

“Our results suggest that the cells that regulate food and control the microbial environment are possible evolutionary precursors of the first animal brains. It really is food for thought,” says Musser.

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