Researchers have discovered that genes involved in the fin ray development of fish are also used in the development of wrists and digits. This helps provide new insight into the evolution of fish into tetrapod animals. The findings are in a paper just published in the journal Nature.
The evolution of fish fins into limbs has long puzzled scientists. It was generally believed that the fin rays of fish were unrelated to the development of tetrapod limbs. Limbs and fin rays develop in very different ways and are also unalike structurally. To fully understand the evolution of four-legged animals, researchers need to solve the mystery of how limbs first developed.
A team of researchers spent three years using a gene editing technique called CRISPR/Cas to study fin ray development in zebrafish. Zebrafish are common laboratory animals and their genome has been studied extensively. By deleting and silencing specific gene combinations, the researchers could learn how different genes affect development. The team focused their attention on Hox genes, a set of important genes responsible for the body plan of a developing embryo.
The team discovered that genes necessary for the formation of wrists and digits were also required for proper fin ray development in zebrafish. If the genes HoxD and HoxA were deleted in mice, the mice failed to develop wrists and toes. If those same Hox genes were deleted in zebrafish, the fish didn’t develop full fin ray structures.
The findings are helping scientists understand the evolution of fish into tetrapods. The researchers are already planning future studies, including experiments to better understand how Hox genes can control such different body plan types. They are also investigating Tiktaalik, a fossil that represents the link between fish and tetrapods. The fossilized fish has many traits found in four-legged animals, making it the focus of evolutionary research since its discovery in 2006.
Tetsuya Nakamura, Andrew R. Gehrke, Justin Lemberg, Julie Szymaszek, Neil H. Shubin. Digits and fin rays share common developmental histories. Nature (2016).