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Humans are related to sea monsters, study reveals

Scientists from the Stowers Institute for Medical Research have identified remarkable similarities in brain development between humans and sea lampreys, ancient creatures that could easily fit the description of sea monsters. 

The researchers, led by Dr. Robb Krumlauf, investigated the evolutionary journey of the vertebrate brain. The results shed light on our shared ancestry with a creature that seems worlds apart from us.

Window into the distant past 

The sea lamprey, a 500-million-year-old species, is a jawless fish known for its distinctive, sharp-toothed suction cup mouth.

Unlike the majority of vertebrates that have jaws, sea lampreys offer a unique perspective into the evolution of critical vertebrate traits. 

This study focused on the hindbrain, the brain’s segment responsible for controlling essential functions such as blood pressure and heart rate.

The findings reveal that both humans and sea lampreys construct this vital part of the brain using a surprisingly similar genetic and molecular toolkit.

“This study on the hindbrain is essentially a window into the distant past and serves as a model for understanding the evolution of complexity,” explained study co-author Dr. Hugo Parker.  

Pivotal molecular cue 

The investigation was focused on a pivotal molecular cue, retinoic acid (commonly known as vitamin A), previously understood to guide the gene circuitry in complex species’ hindbrain development. 

Unexpectedly, this molecular cue is also integral to the development of the sea lamprey’s hindbrain, suggesting a common evolutionary pathway for all vertebrates.

“There was a split at the origin of vertebrates between jawless and jawed around 500 million years ago,” said study lead author Dr. Alice Bedois, a former predoctoral researcher in the Krumlauf Lab.

“We wanted to understand how the vertebrate brain evolved and if there was something unique to jawed vertebrates that was lacking in their jawless relatives.”  

Sea lamprey hindbrain 

Previous collaborations between the Krumlauf Lab and Dr. Marianne Bronner at the California Institute of Technology had established that the genes structuring the sea lamprey hindbrain are identical to those in jawed vertebrates, including humans. 

However, the new study uncovers the broader role of retinoic acid in initiating this gene circuitry, underscoring the ancestral nature of this developmental process across vertebrates.

Unexpected discovery 

While the researchers knew that retinoic acid cues the gene circuitry to build the hindbrain in complex species, it was not thought to be involved for more simple animals like sea lampreys. 

The experts were surprised to find that the sea lamprey core hindbrain circuit is also initiated by retinoic acid, providing evidence that these sea monsters and humans are much more closely related than anticipated.  

The discovery challenges previous assumptions about the sea lamprey’s brain development. “We found that not only are the same genes but also the same cue is involved in sea lamprey hindbrain development, suggesting this process is ancestral to all vertebrates,” said Dr. Bedois.    

Crucial signaling molecule 

The research not only bridges an evolutionary gap between humans and sea lampreys but also emphasizes the role of retinoic acid as a crucial signaling molecule in vertebrate development.

“People thought that because sea lampreys lack a jaw, their hindbrain was not formed like other vertebrates,” said Dr. Krumlauf. “We have shown that this basic part of the brain is built in exactly the same way as mice and even humans.”  

Study implications 

The implications of this research extend beyond the fascinating comparison between humans and sea monsters. 

The study opens new avenues for understanding the diversity among vertebrates, suggesting that while the blueprint for hindbrain formation is conserved, other mechanisms contribute to the vast variety observed in the animal kingdom.

“We all derived from a common ancestor,” said Bedois. “Sea lampreys have provided an additional clue. Now we need to look even further back in evolutionary time to discover when the gene circuitry governing hindbrain formation first evolved.”   

The study is published in the journal Nature Communications.


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