The little skate is a fish. But it is also known for walking with its fins-like legs. It is much like terrestrial vertebrates. The little skate diverged from a common ancestor with terrestrial tetrapods. It was around 470 million years ago. Previous research found that the motor nerve network involved in walking in little skates and tetrapods is similar. But studying the molecular mechanism of how these motor nerve networks evolved was difficult. Because a high-quality whole-genome of the little skates was lacking.
Now a research team used the most recent genome analysis technology to create a high-quality whole-genome of the little skate. The study is published in eLife. The newly constructed whole-genome of the little skate is 2.13 gigabytes in size. It is 93% of the predicted genome size and also a high-quality whole genome with 17,230 protein-encoding genes.
The research team also conducted a comparison with terrestrial animals. They have used the high-quality whole-genome of the little skate. They have performed a comparative analysis of the transcriptomes of the little skate and tetrapod motor neurons. Through this study, genes expressed in common and genes expressed differentially in motor neurons were identified.
Walking with fins requires 10 muscles in the little skate. But moving the limbs requires 50 muscles in tetrapods. The researchers proposed a molecular mechanism for how the simple walking pattern and the sophisticated movements seen in terrestrial tetrapods evolved during evolution by comparing the two species.
Professor Baek Myung-In of the Department of Brain Sciences at DGIST led this study. The study was carried out in collaboration with research teams from Seoul National University and New York University Medical School. The study presented the molecular mechanism of the evolution of walk-related motor nerve networks. It has brought together specialised research capabilities in comparative biology, genomics, and neurobiology.
More information: DongAhn Yoo et al, Little skate genome provides insights into genetic programs essential for limb-based locomotion, eLife (2022). DOI: 10.7554/eLife.78345