A change brought this fish from the fins to the limbs

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Like exactly that it could have happened hundreds of millions of years ago, however, it has long been an evolutionary mystery that has baffled scientists.

Now, American scientists say they may have stumbled upon a possible answer.

By modifying a single gene, researchers at Harvard University and Boston Children’s Hospital have designed zebrafish that showed the onset of simple appendages.

To answer how animals made the transition from sea to land, scientists have traditionally looked at the fossil record. But over the past 30 years, scientists have been looking for changes in genes that could explain the passage from the fin to the modern limb.

“The most amazing thing for me is that such a dramatic change in the fin and musculature skeleton is possible with a single mutation,” said Brent Hawkins, a postdoctoral researcher at Harvard University and Boston Children’s Hospital. first author of the study he published Thursday in the journal Cell.

“Prior to this discovery, the transition from the fin to the limb was supposed to involve multiple changes in a myriad of genes,” he noted by email.

“Of course, this transformation was a very gradual and complex process, but our mutants show that it could also have involved rapid jumps and that developing animals are able to incorporate new bones quite easily.”

This illustration, produced by the study’s researchers, shows (from the left) how a human limb has multiple long bones that allow for a wide range of movements; the fin skeleton of a normal zebrafish that has no joint; and that of a mutant zebrafish, with new bones moving away from the body with a pattern similar to the limbs.

Innate capacity

Although previous research has identified genes that are needed to make fin and limb bones, no one has previously found a genetic change that causes the fin to change to a more fin-like pattern, Hawkins explained for e-mail.

The mutation found by the researchers causes a change in the bones of the pectoral fins of the zebrafish, which adhere to the shoulder joint of the fish in the same way that the human arm adheres to the shoulder. .

A new set of long bones, called intermediate radii, develops that form a joint similar to a human elbow. Genetic change includes new muscles and joints that are found in the limbs, but not in the simple fins.

The discovery by scientists has shown that fish, which had been thought to have lost the machinery needed to evolve limbo-like body parts, actually retain an innate ability to form these structures.

Miniature-sized zebrafish have become a key pillar of genetic research. They are easy to maintain in large numbers and reproduce easily, with a single mating pair producing hundreds of eggs each week. These fish are also soft and easy to handle, in addition to their eggs and embryos are translucent and easy to examine.

The researchers mutated the zebrafish genes at random and then systematically examined the fish to find those that underwent interesting changes in their shape, in this case tongue-like structures.

They then sequenced the DNA to find out which genes were affected before using the CRISPR gene editing tool, a method for modifying genes that won the Nobel Prize in Chemistry last year.

This genetic link between fins and limbs could, with further research, shed light on how some animals made the transition from sea to land and what genetic mechanics are needed to make it a reality.

One of the questions the team hopes to examine below is whether the new bones change the way zebrafish fins work and how the fish moves.

“That such complex and coordinated changes could result from a single DNA letter change was quite shocking and reveals that our fish ancestors had the raw genetic material and the latent ability to create limbs,” Hawkins said.

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