Metazoan-wide phylogenomics supports the emergence of recognisable canonical prostanoid-receptor family structure across the vertebrate transition
This metazoan-wide phylogenomic study demonstrates that the canonical eight-family structure of prostanoid receptors is a vertebrate-specific innovation, revealing that previously proposed non-vertebrate homologs are actually distinct receptor lineages whose apparent similarity to vertebrate EP4 receptors stems from phylogenetic proximity rather than true orthology.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
Inside the bodies of animals, from the simplest sea sponges to complex humans, a sophisticated chemical language coordinates vital processes like inflammation, blood flow, and reproduction. This language relies on a group of lipid molecules called prostanoids, which act as local messengers. To receive these messages, cells use specialized proteins embedded in their outer walls, known as receptors. In vertebrates, such as fish, birds, and mammals, these receptors are organized into eight distinct families, each tuned to a specific type of prostanoid signal. Scientists have long assumed that this complex eight-family system was inherited from ancient ancestors, meaning that even creatures without backbones, like jellyfish or insects, should possess the direct evolutionary predecessors of these eight specific families.
A new study challenges this long-held assumption by looking at the genetic history of these receptors across the entire animal kingdom. The research, led by independent researcher Sebastiano Scibelli, set out to determine when and how the recognizable structure of these eight receptor families actually emerged. By analyzing thousands of genetic datasets from hundreds of animal species, the study reveals that the specific eight-family arrangement found in vertebrates is not a feature of all animals, but rather a development that appeared specifically during the transition to vertebrates.
The researcher began by gathering a massive amount of genetic data, examining protein sequences from over 3,000 species representing 30 different animal groups. They compared these sequences against a carefully curated set of 78 known vertebrate receptors, which serve as the standard reference for the eight families. The goal was to see if any of the non-vertebrate animals possessed receptors that fit neatly into these eight established categories. The researcher used a rigorous, multi-step process to ensure accuracy. They first cast a wide net to find any potential matches, then applied strict filters to confirm the proteins had the correct structure, and finally placed them on evolutionary trees to see where they belonged. This method allowed them to distinguish between a receptor that is merely similar to a vertebrate one and one that is a true evolutionary relative.
The results were striking. Among the thousands of sequences analyzed from non-vertebrate animals, not a single one could be definitively placed inside any of the eight canonical families. While many of these ancient receptors were related to the prostanoid system in a broad sense, they did not belong to the specific groups known as DP1, EP1 through EP4, FP, IP, or TP. Instead, the non-vertebrate receptors formed their own distinct lineages that branched off before the vertebrate families were fully formed. The researcher found that these ancient receptors often appeared closest to one specific vertebrate family, EP4, but this was a result of the way the evolutionary tree was shaped, not evidence that they were true ancestors of the EP4 family. The researcher demonstrated that this proximity was a geometric artifact of the data rather than a sign of direct lineage.
The study also addressed previous research that had identified specific receptors in sea anemones and corals as direct equivalents to vertebrate EP2 and EP4 receptors. Upon re-examining the genetic sequences with their more comprehensive and rigorous methods, the author found that these assignments were incorrect. The sequences from the sea anemone were indeed related to the prostanoid system but did not fit the specific EP2 or EP4 categories. More significantly, the sequences from the coral, which had been labeled as EP2 and EP4, were actually unrelated to the prostanoid receptor family entirely, belonging instead to different groups of cell-surface proteins. This suggests that earlier studies, which relied heavily on simple similarity searches, may have misidentified these ancient proteins.
The emergence of the recognizable eight-family structure appears to have happened gradually as vertebrates evolved. The study indicates that the clear separation into the eight distinct families became established across the transition from early chordates to jawed vertebrates. While some early vertebrate groups, like lampreys and hagfish, showed signs of this emerging structure, the full, stable arrangement was not yet complete. It was only in the ancestors of modern jawed vertebrates that the system solidified into the eight families seen today. The researcher also looked at the physical location of these genes on chromosomes to understand how they multiplied. They found that while some pairs of receptors remained close together on the same chromosome, suggesting they were created by local duplication, others were scattered, hinting at a more complex history involving large-scale genome duplications. However, the data did not support a simple model where all eight families were created simultaneously by a single ancient event.
This work fundamentally changes our understanding of how animal signaling systems evolved. It shows that the ability to respond to prostanoid signals is ancient and widespread, existing in many forms across the animal kingdom. However, the specific, highly organized eight-family system that defines vertebrate biology is a later innovation. The receptors found in invertebrates are not broken or incomplete versions of the vertebrate system; they are a diverse, independently evolving pool of proteins that served similar functions but followed a different evolutionary path. The study concludes that the complexity of the vertebrate prostanoid system is a unique feature of that lineage, arising from a mix of local gene duplications and larger genomic events, rather than being a direct inheritance from a pre-existing, fully formed invertebrate ancestor.
Drowning in papers in your field?
Get daily digests of the most novel papers matching your research keywords — with technical summaries, in your language.