A key gene has been identified that explains the repeated emergence of planning ability during the evolution of marsupials. People say “When pigs fly” to describe the impossible. But although most mammals live on land, the ability to glide or fly has evolved many times over the course of mammal evolution in species ranging from bats to flying squirrels.

How was it? A study recently published in the journal NatureA team of researchers led by Princeton University and Baylor College of Medicine describes the genomic and developmental basis of the patagium, the thin skin membrane that allows some mammal species to fly.

“We don’t fully understand how new traits and adaptations arise from a molecular and genetic perspective. “We wanted to investigate how evolutionary innovation occurs,” said co-author Dr. Ricardo Mallarino, an associate professor of molecular biology at Princeton.

To better understand the evolution of Patagium, the team focused on marsupials. This is because the ability to glide has evolved many times using similar anatomical changes in closely related marsupials such as the sugar glider, a tiny marsupial that is small enough to fit in your pocket and popular as an exotic pet.

Genetic view of gliderism

The Baylor team sequenced the genomes of 15 marsupial species and determined the DNA sequences of both flying species and their non-flying relatives. Comparison of these sequences revealed accelerated evolution near a gene called Emx2.

“The interesting thing is that the gene sequence itself does not appear to be where the most significant changes occur. Instead, significant changes occur in short stretches of DNA called “enhancers” that are located close together in the genome. This is what changes how and where Emx2 is active in the body.” they are variable enhancers, and this drives the evolution of the shift,” said co-author Dr. Erez Lieberman on Aiden Baylor.

Evolutionary mechanisms and experimental approaches

“It’s important to understand the fundamental changes that occur at the genomic level that lead to these convergent traits, because that can tell us whether evolution follows the path of least resistance. You can get the same result but take different paths to get there,” says the first, a graduate student in Mallarino’s lab. Author Jorge Moreno.

The researchers then wanted to test these ideas. To do this, they used one of the most unique features of marsupials: their bags. One of the authors, Dr. D., is an associate professor of molecular and human genetics at Baylor and a researcher at Rice University’s Center for Theoretical Biological Physics. “Marsupials are born at a much earlier stage of development than normal mammals,” said Olga Dudchenko. “Instead of continuing to develop in their mother’s womb, they burrow into her pouch and stay there until they’re ready to take on the world on their own. Having them right here in the pouch makes it much easier to study how individual genes like Emx2 affect marsupial development.”

The researchers showed that Emx2 initiates marsupial patagium through a genetic program that is likely present in all mammals. For example, Emx2 is active in the parietal skin of mice and sugar gliders, but is expressed much longer in sugar gliders. As Dudchenko of the Center for Genome Architecture at Baylor puts it, “By modifying these critical Emx2 enhancers, species after species have used this universal program to evolve the ability to glide.”