Scientists discover essential component that helps killifish regenerate their fins

Spontaneous injuries like limb loss or spinal cord damage are impossible for humans to repair. Yet some animals have an extraordinary ability to regenerate after injury, a response that requires a precise sequence of cellular events. Now, new research from the Stowers Institute for Medical Research has uncovered a critical temporal factor – specifically the length of time cells actively respond to injury – involved in regulating regeneration.

A recent study published in iScience on September 20, 2024, sought to understand exactly how an organism knows how much tissue has been lost after injury. Led by former predoctoral researcher Augusto Ortega Granillo, Ph.D., in the laboratory of Stowers President and Chief Scientific Officer Alejandro Sánchez Alvarado, Ph.D., the team studied how African killifish properly regrow their tail fins after damage.

By analyzing tissue dynamics during regrowth, they discovered that in addition to known factors, including the number of participating cells and their location, the length of time cells participate in the repair process is also critical.

“One of the greatest unsolved mysteries of regeneration is how an organism knows what has been lost after injury,” said Sánchez Alvarado. “Essentially, the study points to a new variable in the regeneration equation. If we can modulate the rate and duration at which a tissue can initiate a regenerative response, it could help us design therapies that can activate and perhaps to prolong the regeneration response of tissues that normally would not.

Shortly after an injury to a killifish’s tail, the remaining tissues must experience the extent of the damage. Next, this tissue must attract the right number of repair cells to the site of injury for the appropriate length of time. Damage detection, repair cell recruitment, and timing must somehow work together to regrow the tail.

“If an animal capable of regenerating extremities, such as a tail, only loses a tiny part, how does it know that it should not regenerate a whole new tail but just the missing piece?” said Sánchez Alvarado. To answer this question, the team surveyed different wound locations in the killifish’s caudal fin.

They found that skin cells, both near an injury and in distant, uninjured areas, initiate a genetic program that primes the entire animal to prepare for a repair response. Then, skin cells at the site of injury maintain this response and temporarily change state to alter the surrounding material called the extracellular matrix.

Ortega Granillo likens this matrix to a sponge that absorbs signals secreted by injured tissue and then guides repair cells to get to work. If the signals are not received or interpreted correctly, the regeneration process may not restore the original shape and size of the tail.

“We have very clearly defined when and where – 24 hours after injury and in the extracellular matrix – the transient cellular state acts in fin tissue,” Ortega Granillo said. “Knowing when and where to look allowed us to cause genetic disruptions and better understand how these cellular states function during regeneration.”

To determine whether these distinct cellular states communicate information to the extracellular matrix (the supporting structure surrounding cells) during the repair process, the researchers used the CRISPR-Cas9 gene editing technique. They specifically targeted a gene known to modify the extracellular matrix, because they had observed its activation early in the regeneration response.

By disrupting the function of this gene, the team sought to determine its role in relaying information from cells to the matrix during regeneration.

“These modified animals no longer know how much tissue has been lost,” Ortega Granillo said. “They still regenerated, but the rate of tissue growth was deficient. This tells us that by changing the extracellular space, the skin cells are telling the tissue how much is being lost and how fast it should grow .”

Indeed, the speed and amount of tissue regenerated in these genetically modified killifish increased, whether the tail injury was mild or severe. This finding opens the possibility that cellular states that modify the matrix increase regenerative regrowth. If cellular states could be fine-tuned, this could provide a way to stimulate a more robust regenerative response.

From an evolutionary perspective, understanding why some organisms excel at regeneration while others, such as humans, have limited regenerative capabilities is a driving force in the field of regenerative biology. By identifying general principles in organisms with high regenerative capacity, researchers potentially aim to apply this knowledge to improve regeneration in humans.

This comparative approach not only highlights the evolutionary aspects of regeneration, but is also promising for the development of new therapeutic strategies in regenerative medicine.

“Our goal is to understand how to shape and grow tissues,” Ortega Granillo said. “For people who experience injury or organ failure, regenerative therapies could restore function compromised during illness or following injury.”

Other authors include Daniel Zamora, Robert Schnittker, Allison Scott, Alessia Spluga, Jonathon Russell, Carolyn Brewster, Eric Ross, Daniel Acheampong, Ning Zhang, Ph.D., Kevin Ferro, Ph.D., Jason Morrison, Boris Rubinstein, Ph.D., Anoja Perera and Wei Wang, Ph.D.