To find out what controls the formation of sensory legs, they had to grow sea robins from eggs. The research team observed that the legs of sea robins develop from the three pectoral fin rays located around the fish's stomach area, then detach from the fin as they continue to develop. One of the most active genes in the developing legs is the transcription factor (a protein that binds to DNA and turns genes on and off), known as tbx3a. When genetically engineered sea breasts had tbx3a edited with CRISPR-Cas9, it resulted in fewer legs, deformed legs, or both.
“Disruption of tbx3a results in upregulation of pectoral fin markings before leg separation, indicating that leg rays become more fin-like in the absence of tbx3a,” the researchers said in a second study, also published in Current Biology.
To see whether genes for sensory legs are a dominant trait, the research team also tried creating seabreast hybrids, crossing species with and without sensory legs. This resulted in offspring with legs that had sensory abilities, indicating that it is a genetically dominant trait.
Exactly why sea robins evolved the way they did is still unknown, but the research team came up with a hypothesis. They think that the paws of the ancestors of seals were originally intended for locomotion, but gradually they began to acquire some sensory use, allowing the animal to search the visible surface of the seabed for food. The fish that had to search deeper for food developed sensory legs that allowed them to taste and dig for hidden prey.
“Future work will leverage the remarkable biodiversity of sea robins to understand the genetic basis of novel traits and diversification in vertebrates,” the team also said in the first study. “Our work provides a basis for understanding how new properties evolve.”
Current Biology, 2024. DOI: 10.1016/j.cub.2024.08.014, 10.1016/j.cub.2024.08.042
