Researchers have traced the origins of critical cells in vertebrate evolution by studying lampreys, a group of primitive, bloodsucking fish. Lampreys, notable for their lack of jaws and intimidating appearance, possess a cell population essential to the origins of vertebrates, according to a study published on July 26 in *Nature Ecology and Evolution*.
Vertebrates, including humans, trace their lineage back to ancient fish from over 400 million years ago during the Devonian period. During this time, jawless fish were prevalent, while jawed vertebrates were rare. Today, the situation is reversed.
Lampreys and hagfish are the only surviving groups of the once-dominant jawless vertebrates and are among the most primitive living vertebrates. Studying their genes can help researchers understand early vertebrate evolution. “Lampreys may hold the key to understanding where we came from,” said Carole LaBonne, a professor of molecular biosciences at Northwestern University. To comprehend evolutionary features, scientists need to look at the most primitive versions of the animals being studied, which leads them back to lampreys and hagfish.
LaBonne and her colleagues compared lamprey genes with those of jawed, aquatic frogs called Xenopus, focusing on genes regulating a stem cell population called the neural crest. This cell population, found only in vertebrates, was crucial for vertebrate evolution. These stem cells contribute to diverse cell types, tissues, and structures essential to vertebrate origin and diversification.
The team found a similar gene network in both animals, with one significant difference: a gene called pou5 was not expressed in the neural crest cells of lampreys, potentially explaining why lampreys are jawless.
The researchers also examined pluripotent blastula cells, primitive cells linked to the evolution of the neural crest. These cells can potentially become all other cell types in the body. The scientists found that lampreys and Xenopus had an intact pluripotency network within their blastula cells, suggesting that these cell types evolved at the beginning of the vertebrate family tree.
The researchers hypothesized that pou5, present in both lamprey and Xenopus blastula cells, was lost from the neural crest of jawless vertebrates. Joshua York, the study’s first author, noted that even though pou5 isn’t expressed in a lamprey’s neural crest, it could promote neural crest formation in frogs, indicating this gene is part of an ancient pluripotency network present in our earliest vertebrate ancestors.
