A recent study conducted by experts from the Centre for Genomic Regulation has discovered that the cellular components of the brain were present in shallow seas approximately 800 million years ago. Through the examination of placozoans, small marine animals, researchers have gained insights into the evolutionary journey of neurons.
Placozoans, which are about the size of a large grain of sand, live in warm and shallow waters and feed on algae and microbes. Despite the lack of organs or distinct body parts, placozoans are considered one of the five main animal lineages, along with ctenophores, sponges, cnidarians, and bilaterians.
A key element for the existence of placozoans is peptidergic cells, which release peptides that regulate their feeding and movements. The study used molecular and computational analyses to create cellular atlases in order to understand the evolution and function of these cells. It was discovered that these peptidergic cells served as precursors to modern neurons.
The researchers uncovered an intricate network of “intermediate” cell types connecting the nine main cell types in placozoans. Additionally, peptidergic cells, unlike other cells, exhibited a surprising similarity to neurons that appeared millions of years later in more advanced organisms. This unique resemblance to neurons was not observed in primitive species such as sponges or ctenophores.
The study revealed three notable parallels between peptidergic cells and neurons. Firstly, the placozoan cells differentiate in a similar manner to neurogenesis observed in cnidarians and bilaterians. Secondly, these cells possess many components of the synaptic terminal of a neuron but lack the characteristics of a true neuron, such as electrical signal conduction. Lastly, deep learning revealed that these cells communicate through GPCRs initiated by neuropeptides, reflecting neuronal communication.
By highlighting the evolutionary lineage, the research indicates that the fundamental components of neurons began to develop in ancient seas 800 million years ago. Approximately a century after the appearance of their predecessors, the peptidergic cells of placozoans likely evolved to possess critical features essential for neurons, such as ion channels and postsynaptic scaffolds.
While the first modern neuron is estimated to have appeared around 650 million years ago, neuron-like cells exist in ctenophores with distinctive characteristics, raising questions about the evolutionary trajectory of neurons. The authors of the study emphasize the need for further research to address these open questions and gain a clearer understanding of the evolutionary paths of neurons and other cell types.
As genomic sequencing continues to advance, it is expected that secrets held by non-traditional model animals such as placozoans, ctenophores, and sponges will gradually be unveiled, shedding more light on the evolutionary history of life.
– Cell Journal
– Centre for Genomic Regulation