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In fact, many multifunctional cells in sponges typically represent gene modules associated with specialized cells in more complex animals, such as vertebrates. For example, sponge neuroid cells not only represent some presynaptic machinery of neurons, they also represent immune genes. (If neuroid cells are likely to control the microbial contents of sponge digestive chambers, these immune genes contribute to this task.) Sponges also have cells called pinacocytes, like muscle cells, that contract together to squeeze animals and eliminate debris or unwanted waste. ; pinacocytes have sensory machinery that responds to nitric oxide, a vasodilator.
“Nitric oxide is what relaxes the smooth muscle in our blood vessels, so when our blood vessels expand, it’s nitric oxide that causes that relaxation,” Musser said. “And through experiments on paper we have shown that nitric oxide also regulates the contractions of this sponge.” Like glutamate, nitric oxide suggests that it may have been part of an early signaling mechanism to coordinate primitive behaviors in the sponge.
“Our data are very consistent with the idea that many important functional machinery existed in early animal evolution with this idea,” Musser said. “And a lot of the early evolution of animals was to start dividing this into different cells. But probably these first cell types were very multifunctional, and they had to do a lot of different things.” The first animal cells, like their close relatives protozoa, were probably supposed to be cellular knives of the Swiss army. As multicellular animals evolved, their cells may have taken on different roles, which may have led to the division of labor into more specialized cell types. But different animal lineages have divided things in different ways and on different levels.
If mixing and pairing genetic modules was a crucial issue in the early evolution of animals, then comparing the organization and expression of these modules in different species could tell us their history, and how they can be happily mixed about possible limitations. He is a researcher looking for these answers Arnau Sebé-Pedrós, Which studies the evolution of cell types at the Center for Genomic Regulation in Barcelona and published the first atlases of cell types in sponges, placozoans and comb jelly in 2018.
Sebé-Pedrós believes that the spatial configuration of genes across chromosomes can be revealing because genes placed together can share regulatory machinery. “I am absolutely amazed at the level of conservation of gene order in animal genomes,” he said. He suspects that the need to regulate a set of functionally related genes keeps them in the same chromosomal neighborhood.
Scientists are in the early stages of learning how cell types evolve and how they relate to each other. But as important as it is to shed light on the muddy origins of animal evolution, sponge cell atlases are also making a major contribution to revealing the possibilities available in animal cell biology. “It’s not important for us to understand the origin of animals themselves,” said Sebé-Pedrós, “as well as to understand things that may be completely different from anything else we know about other animals.”
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Original story reprinted with permission Quanta Magazine, independent editorial publication Simons Foundation its mission is to improve public understanding of science by covering developments and trends in mathematical and physical and life sciences research.
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