Amazing stuff!
"A study in the journal Cell sheds new light on the evolution of neurons, focusing on the placozoans, a millimeter-sized marine animal. Researchers ... find evidence that specialized secretory cells found in these unique and ancient creatures may have given rise to neurons in more complex animals. ...
These animals, thought to have first appeared on Earth around 800 million years ago, are one of the five main lineages of animals alongside Ctenophora (comb jellies), Porifera (sponges), Cnidaria (corals, sea anemones and jellyfish) and Bilateria (all other animals).
The sea creatures coordinate their behavior thanks to peptidergic cells, special types of cells that release small peptides which can direct the animal's movement or feeding. ..."
From the highlights and abstract:
"Highlights
• Comparative single-cell genomics reveals cell type diversity in the phylum Placozoa
• Fourteen placozoan peptidergic cell types expressing neuronal genes
• Post-translationally modified neuropeptides define elaborate cell signaling network
• Peptidergic progenitors with neurogenesis-like differentiation from epithelial cells
Summary
The assembly of the neuronal and other major cell type programs occurred early in animal evolution. We can reconstruct this process by studying non-bilaterians like placozoans. These small disc-shaped animals not only have nine morphologically described cell types and no neurons but also show coordinated behaviors triggered by peptide-secreting cells. We investigated possible neuronal affinities of these peptidergic cells using phylogenetics, chromatin profiling, and comparative single-cell genomics in four placozoans. We found conserved cell type expression programs across placozoans, including populations of transdifferentiating and cycling cells, suggestive of active cell type homeostasis. We also uncovered fourteen peptidergic cell types expressing neuronal-associated components like the pre-synaptic scaffold that derive from progenitor cells with neurogenesis signatures. In contrast, earlier-branching animals like sponges and ctenophores lacked this conserved expression. Our findings indicate that key neuronal developmental and effector gene modules evolved before the advent of cnidarian/bilaterian neurons in the context of paracrine cell signaling."
Tiny sea creatures reveal the ancient origins of neurons (primary news source) A study in the journal Cell sheds new light on the evolution of neurons, focusing on the placozoans, a millimetre-sized marine animal. Researchers ... find evidence that specialised secretory cells found in these unique and ancient creatures may have given rise to neurons in more complex animals.
Graphical abstract:
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