Can You Tell What This Fish Embryo Is Growing Place of Fins?

Most finned animals don't have a sea witch named Ursula to grant their "Little Mermaid" wish to bear legs instead of fins, but a group of researchers seem to have conducted a similar switch of appendages at the embryonic level.

In an effort to better understand how animals made the evolutionary leap from sea to land, researchers have manipulated a fish's genes to achieve just this result. They've grown a fish embryo whose fins were more reminiscent of limbs meant for land.

Zebrafish manipulated to develop an appendage that looks more like a leg and than fin. (Image: Freitas et al., Developmental Cell)

According to the research published in the journal Developmental Cell, a team led by Dr. José Luis Gómez-Skarmeta of the CSIC-Universidad Pablo de Olavide-Junta de Andalucía, in Seville, Spain, introduced a gene (Hoxd13, a gene known to play a role in distinguishing body parts) to a zebrafish's fin tip. They found the appendage, instead of stopping as a stubby fin, kept growing.

"First, and foremost, this finding helps us to understand the power that the modification of gene expression has on shaping our bodies," Gómez-Skarmeta said in a statement.

The researchers increased Hoxd13 in the fish and it began to express more limb-like fins. (Image: Developmental Cell)

The researchers believe a new piece of DNA could have been introduced that would control this limb-producing gene's expression. The scientists know of a DNA control element in mice that regulates activation of the Hoxd13 gene, but isn't present in fish.

Here's how Popular Science explained it:

Their lab findings led the researchers to hypothesize that the secret to limb development may have been a new element in some lobe-finned fish's DNA. When present, this DNA element would have helped turn on the Hoxd13 gene on the fish embryo's fins, leading them to lengthen and grow into limbs.

"We found that in the zebrafish, the mouse Hoxd13 control element was capable of driving gene expression in the distal fin rudiment. This result indicates that molecular machinery capable of activating this control element was also present in the last common ancestor of finned and legged animals and is proven by its remnants in zebrafish," co-author Dr. Fernando Casares said the research statement.