Jawless, bloodsucking lampreys may seem like creatures out of a nightmare, but they hold a key to understanding how humans and all other vertebrates evolved. A new study, published in the journal Nature Ecology and Evolution, reveals that lampreys – known for their lack of jaws and terrifying appearance – possess a cell population that played a crucial role in the early evolution of vertebrates.
Vertebrates, including humans, trace their lineage back to ancient fish that swam the seas over 400 million years ago during the Devonian period. At that time, jawless fish like lampreys were plentiful, while jawed vertebrates were rare. Today, the situation is reversed, with lampreys and hagfish being the only surviving groups of the once-dominant jawless vertebrates. Their primitive nature makes them ideal for studying early vertebrate evolution.
“Lampreys may hold the key to understanding where we came from,” said study author Carole LaBonne, a professor of molecular biosciences at Northwestern University. “In evolutionary biology, if you want to understand where a feature came from, you can’t look forward to more complex vertebrates that have been evolving independently for 500 million years. You need to look backwards to the most primitive version of the animal you’re studying, which leads us back to hagfish and lampreys – the last living examples of jawless vertebrates.”
LaBonne and her team compared lamprey genes with those of Xenopus, a group of jawed, aquatic frogs. They focused on genes that regulate a stem cell population called the neural crest, which is unique to vertebrates and played a vital role in their evolution. These stem cells are critical to the vertebrate body plan, contributing to diverse cell types, tissues, and structures essential to the origin and diversification of vertebrates.
The researchers discovered a similar gene network in both lampreys and Xenopus, with one significant exception. A stem cell-regulating gene called pou5 was not expressed in the neural crest cells of lampreys, potentially limiting their ability to develop heads and jaws. This could explain why lampreys lack jaws.
The study also examined pluripotent blastula cells, more primitive cells believed to be linked to the evolution of the neural crest. These cells possess the potential to become all other cell types in the body, a characteristic known as pluripotency, and are crucial for determining body plans. The scientists found that both lampreys and Xenopus had a complete pluripotency network within their blastula cells, suggesting that blastula and neural crest stem cells evolved early in the vertebrate family tree.
The researchers hypothesize that pou5, present in both lamprey and Xenopus blastula cells, was likely present when the ancestor of jawed and jawless vertebrates first evolved. This gene was subsequently lost from the neural crest of jawless vertebrates.
“While most of the genes controlling pluripotency are expressed in the lamprey neural crest, the expression of one of these key genes – pou5 – was lost from these cells,” said lead author Joshua York, a researcher in the molecular biosciences department at Northwestern University. “Amazingly, even though pou5 isn’t expressed in a lamprey’s neural crest, it could promote neural crest formation when we expressed it in frogs, suggesting this gene is part of an ancient pluripotency network that was present in our earliest vertebrate ancestors.”
This research provides valuable insights into the evolutionary journey of vertebrates, highlighting the importance of studying seemingly primitive organisms like lampreys to unlock the secrets of our shared ancestry.
