A recent scientific investigation has uncovered remarkable similarities in body formation techniques between sea anemones, creatures belonging to the ancient phylum Cnidaria, and bilaterians, a vast group of animals characterized by bilateral symmetry, which includes humans. This discovery challenges long-held assumptions about the evolutionary timeline of complex biological processes, suggesting that certain fundamental developmental mechanisms may predate the divergence of these major animal lineages.
The study, published in Science Advances, focused on bone morphogenetic protein (BMP) shuttling, a process crucial for establishing body axes in bilaterians. Researchers found that sea anemones employ a similar BMP shuttling mechanism, previously thought to be exclusive to animals with bilateral symmetry. This finding implies that this developmental strategy is far more ancient than previously understood, potentially originating in a common ancestor of both Cnidarians and Bilaterians, which separated over 600 million years ago.
Evolutionary Insights from Sea Anemone Development
Cnidarians, such as sea anemones, jellyfish, and corals, are defined by their radial symmetry, meaning their bodies are organized around a central axis. In contrast, bilaterians possess a distinct front and back, a left and right side, and a top and bottom, facilitating more complex movement and organ systems. The presence of bilaterian-like body patterning mechanisms in radially symmetric cnidarians suggests that the developmental toolkit for bilateral symmetry was present even before the evolutionary split.
David Mörsdorf from the University of Vienna, a lead author of the study, highlighted the significance of this finding. He noted that while not all bilaterians use the Chordin-mediated BMP shuttling pathway identically—for instance, frogs utilize it, but fish do not—the recurrence of this mechanism across distantly related animals points to its role as an ancestral patterning process. The observation that sea anemones also use this technique to shape their body axes strongly indicates its ancient evolutionary origin.
The Role of BMPs and Chordin in Development
Bone morphogenetic proteins (BMPs) function as signaling molecules that guide embryonic cells, dictating their fate and position within the developing organism. These proteins create concentration gradients throughout the body, which are critical for establishing distinct regions and tissues. For example, low BMP concentrations typically signal the development of the central nervous system, moderate levels are associated with kidney formation, and high concentrations can lead to skin development on the belly side.
The research revealed that Chordin, a known BMP inhibitor, also functions as a shuttle for BMPs, mirroring the process observed in bilaterians like fruit flies and frogs. This dual role of Chordin in cnidarians provides compelling evidence that BMP shuttling was likely an established mechanism in the common ancestor of Cnidaria and Bilateria. The evolutionary divergence of these phyla occurred hundreds of millions of years ago, making this a remarkably ancient developmental strategy.
Implications for Evolutionary Biology
The findings challenge the traditional view of cnidarian and bilaterian evolution, suggesting a shared developmental heritage that extends deeper into evolutionary history. While it remains impossible to definitively exclude the possibility of independent evolution of bilateral symmetry in both groups, the study presents a strong case for a common ancestral mechanism.
Grigory Genikhovich, a senior author of the study from the University of Vienna, stated that while independent evolution cannot be entirely ruled out, the evidence leans towards a bilaterally symmetric ancestor utilizing Chordin for BMP shuttling. This common ancestor could have laid the groundwork for the complex body plans seen in bilaterians today, with cnidarians retaining elements of this ancient patterning system despite evolving radial symmetry.
