A team of researchers from Spain and Germany has made a fascinating discovery in simple animals called placozoans, suggesting that the building blocks of our brain cells may have originated billions of years ago.
Placozoans are tiny, grain-of-sand-like creatures. They are primitive organisms consisting of various types of cells and lack organs. They lived in the warm shallow waters of the seas around 800 million years ago, where they fed on microbes and algae.
The researchers, led by cell biologist Sebastián Najle from the Center for Genomic Regulation, found specialized cells in placozoans that exhibit remarkable similarities to neurons found in more complex organisms. These cells, known as peptidergic cells, release peptide signals to coordinate the behavior of placozoans, much like neurons in other animals. Although placozoan cells are not fully developed neurons, they serve as an important evolutionary step.
Through genetic analyses and microscopic screening, the team identified 14 different types of peptidergic cells in placozoans. These cells share some of the same genes as our own neurons but lack certain specialized components necessary for receiving and generating electrical signals. Instead, they use receptor proteins called GPCRs to receive chemical messages, which are common in various types of animal cells.
Interestingly, these peptide-releasing cells are highly conserved in placozoans but are absent in other primitive animals such as sponges and comb jellies. This suggests that the evolution of peptide-secreting cells predates the development of other neuron-like cells. The researchers also raise intriguing questions about the evolutionary origins of neurons. Did neurons evolve once and then diverge, or did they evolve multiple times in parallel?
Understanding how cells evolve and change over time is crucial for unraveling the history of life’s evolution. Placozoans, along with other non-traditional animals like comb jellies and sponges, hold fascinating secrets that scientists are only just beginning to uncover.