Najle, co-first author of the study and postdoctoral researcher at the Centre for Genomic Regulation. "We were astounded by the parallels," says Dr. These outside signals are mediated by neuropeptides, chemical messengers used by neurons in many different physiological processes. However, these cells are far from being a true neuron, as they lack the components for the receiving end of a neuronal message (post-synaptic) or the components required for conducting electrical signals.įinally, the authors used deep learning techniques to show that placozoan cell types communicate with each other using a system in cells where specific proteins, called GPCRs (G-protein coupled receptors), detect outside signals and start a series of reactions inside the cell. Second, they found that peptidergic cells have many gene modules required to build the part of a neuron which can send out a message (the pre-synaptic scaffold). First, the researchers found that these placozoan cells differentiate from a population of progenitor epithelial cells via developmental signals that resemble neurogenesis, the process by which new neurons are formed, in cnidaria and bilateria. The similarities between peptidergic cells and neurons were threefold. Cross-species analyses revealed these similarities are unique to placozoans and do not appear in other early-branching animals such as sponges or comb jellies (ctenophores). Surprisingly, the peptidergic cells shared many similarities to neurons - a cell type which didn't appear until many millions of years later in more advanced animals such as and bilateria. The researchers also found fourteen different types of peptidergic cells, but these were different to all other cells, showing no in-between types or any signs of growth or division. The cells grow and divide, maintaining the delicate balance of cell types required for the animal to move and eat. The research showed that the main nine cell types in placozoans appear to be connected by many "in-between" cell types which change from one type to another. Finally, they carried out cross-species comparisons to reconstruct how the cell types evolved. They then created a map of the regulatory regions in DNA that control these gene modules, revealing a clear picture about what each cell does and how they work together. The maps or 'cell atlases' allowed researchers to chart clusters or 'modules' of these genes. Each cell type has a specialised role which comes from certain sets of genes. The researchers first made a map of all the different placozoan cell types, annotating their characteristics across four different species. Driven by the intrigue of the origin of these cells, the authors of the study employed an array of molecular techniques and computational models to understand how placozoan cell types evolved and piece together how our ancient ancestors might have looked and functioned. The sea creatures coordinate their behaviour thanks to peptidergic cells, special types of cells that release small peptides which can direct the animal's movement or feeding. 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 blob-like and pancake-shaped creatures are so simple that they live without any body parts or organs. Placozoans are tiny animals, around the size of a large grain of sand, which graze on algae and microbes living on the surface of rocks and other substrates found in shallow, warm seas. Though the complete story of how the first neuron appeared remains to be told, the study demonstrates that the basic building blocks for our brain cells were forming in the ancestors of placozoans grazing inconspicuously in the shallow seas of Earth around 800 million years ago. From an evolutionary point of view, early neurons might have started as something like these cells, eventually gaining the ability to create a complete synapse, form axons and dendrites and create ion channels that generate fast electrical signals - innovations which gave rise to the neuron in more complex animals such as jellyfish. Researchers find evidence that specialized secretory cells found in placozoans, tiny sea creatures the size of a grain of sand, have many similarities to the neuron, such as the genes required to create a partial synapse. Tiny sea creatures reveal the ancient origins of neurons Our brain cell components were forming in shallow seas around 800 million years ago Date: SeptemSource: Center for Genomic Regulation Summary: A new study sheds new light on the origins of modern brain cells.
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