Scientists have revealed that genetic reshuffling in skates has enabled the development of fins that have wing-like qualities, contributing to the evolution of a new body structure. In examining the genome of the little skate, researchers studied topologically associating domains (TADs) – large, enclosed loops of DNA and proteins that introduce non-coding points of DNA called enhancers into contact with genes. TADs have previously been identified as playing a role in leading innovations in evolution in mammals such as female mole gonads, but the research into the genome of skate was the first to study the genomic structure that underpins the evolution of paired appendages.
Planar cell polarity genes within the skate genome were broken up and shifted around within TADs, contributing to the transformation of non-mobile fins into the pectoral fins of skates, which have now been fused with its head. The gene activity in the fins of skate embryos involved the elongation of skate fin cells in one direction, which subsequently influenced the shape of tissue growth. The study underlines the potential of the analysis and comparison of 3D genetic structures to reveal the mechanisms behind evolutionary innovation.
The genome structures of skates, sharks and rays have experienced slower evolution and are more similar to those of ancestral vertebrates than those of zebrafish, which are more commonly utilised in research. This reduced evolutionary activity enables researchers to find important changes and gain a perspective on genome evolution running over a far longer timescale. However, the formation of new fins in skates and their migratory movement toward the head is a process still not fully understood, according to Tetsuya Nakamura, the lead author of the report.
While it is not known whether this new understanding of the evolution of paired appendages could contribute to the development of prosthetic limbs, the advantage of such an approach would not be the “replication of a 10-tonne skate”, but in discovering “mechanisms and principles”, according to Matthew Harris, a researcher at Harvard Medical School who was not invovled in the study.