Evolution: development of neuropeptides (Introduction)

by David Turell , Friday, June 03, 2022, 19:55 (693 days ago) @ David Turell

Appeared way before brains appeared:

https://www.quantamagazine.org/brain-signal-proteins-evolved-before-animals-did-20220603/

"Our human brains can seem like a crowning achievement of evolution, but the roots of that achievement run deep: The modern brain arose from hundreds of millions of years of incremental advances in complexity. Evolutionary biologists have traced that progress back through the branch of the animal family tree that includes all creatures with central nervous systems, the bilaterians, but it is clear that fundamental elements of the nervous system existed much earlier.

"How much earlier has now been made dramatically clear by a recent discovery by a team of researchers at the University of Exeter in the United Kingdom. They found that the chemical precursors of two important neurotransmitters, or signaling molecules used in nervous systems, appear in all the major animal groups that preceded creatures with central nervous systems.

"The big surprise, however, is that these molecules are also present in single-celled relatives of animals, called choanoflagellates. This finding shows that animal neuropeptides originated before the evolution of even the very first animals.

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"A variety of molecules very similar to neuropeptides are made by nearly all the early animal groups, including the ctenophores (comb jellies) and the cnidaria (jellyfish, corals and sea anemones). Even the extremely simple animals called placozoans, which have no cells resembling neurons, make neuropeptides. Sponges seemed to be the only exception, which is why it was generally thought that animal neuropeptides originated in cnidarians or ctenophores, after sponges branched away from the rest of the animal tree.

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"...as he [Yañez-Guerra] began looking for them farther down the animal tree, he stumbled on the realization that choanoflagellates made protein precursors of two mature neuropeptides, phoenixin and nesfatin.

"Their presence in choanoflagellates was a surprise because neuropeptides typically appear in the context of sender and receiver neurons. “In a unicellular organism, it’s more difficult to make sense of,” Yañez-Guerra said. “This shows that these neuronal molecules started evolving even before the need for this extensive communication between cell and cell. That’s why it was kind of shocking.” (my bold)

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"A further search of the gene expression data confirmed Yañez-Guerra’s hunch that phoenixin and nesfatin might be the keys to understanding neuropeptide evolution. Not only were the precursor peptides present in the choanoflagellates, but they were also present in all the early animal groups — even the sponges, where they had been overlooked.

"Given that the precursor molecules in the choanoflagellates are so directly connected to these neuropeptides found in all animals, Burkhardt explained, “The last common ancestor of all animals likely had at least two neuropeptides.”

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"The neuropeptides aren’t the only thing that’s unique about ctenophore nervous systems: The structures of their neural networks are so unusual that researchers suspect they evolved independently of those seen in humans and other animals. Why ctenophores do things differently is a mystery, but it’s clear that nervous systems went through a period of tremendous experimentation and innovation early in their evolution — and that at least some of that experimentation began before animals even existed."

Comment: this is a fantastic discovery. It shows that the evolutionary process depended upon precursors of biochemicals be developed long before needed in new applications (organ forms). The idea Darwin had to study evolution by following comparative anatomy has been discarded by biochemical studiesv and genomic trees being devoloped. dhw has persisted in sticking with the antiquated Darwinian approach of form development which is obviously very discontinuous as the Cabrian gap shows.