Sponge genes hint at origins of neurons and other cells

Indeed, many of the multifunctional cells in sponges display units of genes that are normally associated with specialized cells in more complex animals such as vertebrates. For example, spongiform neurons express not only some mechanisms of presynaptic neurons, but also immune genes. (It is possible that if neurons monitor the microbial content of a sponge’s digestive chambers, these immune genes help in this role.) Sponges also contain cells called pineal cells that contract in unison like muscle cells to squeeze the animal and clear unwanted waste or debris. in it. ; Pineal cells contain some sensory mechanisms that respond to nitric oxide, a vasodilator.

“Nitric oxide is what relaxes the smooth muscles in our blood vessels, so when our blood vessels dilate, nitric oxide causes that relaxation,” Moser said. “And we have already shown through the experiments in the paper that nitric oxide also regulates the contractions of these sponges.” Like glutamate, nitric oxide may be part of an early signaling mechanism to coordinate primitive behaviors in sponges, he suggests.

“Our data are very much in agreement with this idea that a large number of important functional pieces of machinery were present early in animal evolution,” Moser said. “And a lot of early animal evolution was about to start breaking this down into different cells. But it’s possible that these first types of cells were very multifunctional, and they had to do multiple things.” Perhaps the first animal cells, like their protozoan relatives, must have been the Swiss Army’s cellular knives. As multicellular animals evolved, their cells may have played different roles, and division of labor may have led to more specialized cell types. But different animal breeds may have divided things up differently and to different degrees.

If mixing and matching genetic units is an important topic of early animal evolution, comparing the order and expression of those units in different species can tell us about their history — and about the potential limitations of how they are randomly mixed. One researcher looking for those answers is Arnau Sebé-Pedros, who studies cell type evolution at the Barcelona Genome Regulatory Center and who published the first Atlases of cell types in the sponge, Placozoans and combing jelly in 2018.

Sebé-Pedrós believes that the spatial configuration of genes along chromosomes can be apparent because genes located together can share a regulatory mechanism. “I was absolutely shocked by the degree to which gene order is preserved in animal genomes,” he said. He suspects that the need for co-regulation of groups of functionally related genes keeps them in the same chromosomal neighborhood.

Scientists are still in the early days of learning how cell types evolve and relate to one another. But while it is important to elucidate the muddy origins of animal evolution, sponge cell atlases also make a significant contribution by revealing possibilities in animal cell biology. “It is not only important for us to understand the origin of animals, but also to understand things that may be radically different from anything else we know about other animals,” said Sebi Pedros.

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original story Reprinted with permission from Quanta MagazineAnd Independent editorial publication Simmons Foundation Its mission is to advance the general understanding of science by covering research developments and trends in mathematics, the physical sciences, and the life sciences.

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