Lampreys possess a fantastic evolutionary origin

Lampreys, despite being invasive and blood-sucking fish causing havoc in Midwestern fisheries, offer a unique opportunity for scientists to delve into the origins of two crucial stem cells that contributed to vertebrate evolution. According to Northwestern University biologists, lampreys enable valuable insights into the evolution of the gene network that regulates these stem cells and shed light on the reasons behind their lack of mandibles.

The two types of cells in focus are pluripotent blastula cells, which resemble embryonic stem cells, and neural crest cells. Both cell types possess pluripotent properties, meaning they can develop into any other cell type in an organism.

A recent study conducted by researchers compared the genes of lampreys with those of Xenopus, a jawed aquatic frog. Through comparative transcriptomics, the study revealed a strikingly similar pluripotency gene network across jawless and jawed vertebrates. Even the levels of transcript abundance for key regulatory factors exhibited surprising similarities.

However, an important distinction emerged during the study. While blastula cells in both species expressed the pou5 gene, a vital regulator of stem cells, lampreys did not express this gene in neural crest stem cells. This absence of pou5 might have hindered lampreys' neural crest cells from forming the cell types integral to the head and jaw skeleton found in jawed vertebrates.

The research findings, to be published in Nature Ecology & Evolution on July 26, facilitate a deeper understanding of the evolutionary origins of distinct features in vertebrate animals, including humans. By examining and comparing the biology of jawless and jawed vertebrates, scientists can explore the ancient characteristics and common ancestry that underlie the differences observed in gene expression and body structures.

Carole LaBonne, a professor at Northwestern University specializing in developmental biology, stated that lampreys are key to unraveling our origins and highlighted the significance of looking to the most primitive versions of animals for understanding feature development in evolutionary biology.

LaBonne and her team have also previously revealed the connection between the developmental origin of neural crest cells and the retention of the gene regulatory network responsible for pluripotency in blastula stem cells. In this new study, they aimed to explore the evolutionary links between these two stem cell populations.

Observations led by postdoctoral fellow Joshua York demonstrated a remarkable similarity between lamprey and Xenopus, with more shared genes than differing ones. Even though the lamprey's neural crest did not express pou5, the study showcased that when this gene was expressed in frogs, it could promote neural crest formation. This suggests the gene's role as part of an ancient pluripotency network among our earliest vertebrate ancestors.

This groundbreaking exploration further supported the hypothesis that the absence of the gene in particular creatures was not a development specific to jawed vertebrates later on.

An intriguing aspect arising from the study is the stringent constraints observed in gene expression levels required for promoting pluripotency. The question of why such constraints exist between animals separated by 500 million years of evolution remains unanswered, leaving a thought-provoking area for future research.

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