New study reveals fish armor is made up of special neural crest stem cells

The science behind bony scutes is deep and it can only be understood by studying a fish right from its embryonic stage.
Rupendra Brahambhatt
Fish against black background
Fish and its protective body armor


The scales or bony scutes that you see on the body of many fish are made up of dentine, a hard tissue also found in human teeth. However, do you know that fish ancestors were soft-bodied animals and didn’t have such hard, scaly armors to protect themselves?

So then, what led to the development of this armor in thousands of modern-day fish species? A team of researchers at Caltech (California Institute of Technology) recently published a study that attempts to answer this question in detail. 

The Caltech team studied sterlet sturgeon fish (Acipenser ruthenus) embryos in a lab to understand the origin and development of bony scutes and found that a special group of stem cells, known as trunk neural crest cells, gives fish their protective armor.

Stem cells turn into scaly armor

Previous research suggests that neural crest cells are embryonic structures lasting for only a short period of time during embryonic development. However, they are of great importance as they give rise to different types of pigment cells, connective tissues, muscles, cartilage tissues, bones, and heart cells.

During their study, the researchers tagged different embryonic cells using fluorescent dyes and observed the migration of these cells under low-light conditions. They noticed that neural crest cells accumulated at the same spot in the embryo from where scutes were originating. 

In order to further confirm the role of these cells in bony armor formation, they also examined the osteoblast, embryonic structures that give rise to bones. Surprisingly, they found traces of the fluorescent dye associated with neural crest cells in the osteoblast as well. 

Plus, when the researchers studied the gene expression profile of the osteoblast, they detected neural crest gene signatures. “The results definitively show that sterlet trunk neural crest cells give rise to osteoblasts of the scutes,” the researchers note.

Thus, the neural crest was a crucial evolutionary innovation driving the origin and diversification of dermal armor along the entire body axis.” They added.

Why do these findings matter?

The current study sheds light on the fact that transient embryonic structures can drastically influence the evolution of an organism. Fish ancestors that lived 350 million years ago lacked bony scutes. 

The development of a bony armor from the trunk neural crest cells was an evolution strategy they had to adopt later to ensure their survival (not all modern-day fish have scales and armor, though). 

By studying these cells further, scientists can trace the various evolutionary events that turned the soft-bodied ancestors into modern-day scaly fish. 

"This is particularly powerful if we can approach evolutionary questions from a developmental biology perspective since many changes that led to diverse cell types occurred via small alterations in embryonic development,” said Marianne E. Bronner, one of the study authors and Edward B. Lewis professor of biology at Caltech. 

According to the researchers, connecting embryonic development with evolution could help scientists fill the many knowledge gaps they encounter while studying different modern and ancient creatures.

The study is published in the journal PNAS.

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