Skate embryo at early developmental stages
David Gold, Lynn Kee, Meghan Morrissey, Embryology Course, Marine Biology Laboratory
Skates got their wing-like fins with the help of gene shuffling, which brings different sections of the genome into physical contact with each other. This created new patterns of gene activity in the fins of skate embryos, highlighting how changes in three-dimensional genomic structure can drive the evolution of new body structures.
Evolutionary biologists are fascinated by fish fins because they represent one of the great innovations of vertebrates: a pair of appendages. These show an amazing variety of shapes, including our arms. In skating, this is the front or pectoral fin that extends forward and merges with the head.
Tetsuya Nakamura, a developmental biologist at Rutgers University (NJ, USA), says, “Somehow, the pectoral fins and head are perfectly combined and integrated in terms of function and structure.” A worthy animal.”
To investigate how fins evolved, Nakamura’s team collaborated with five other groups to examine the 3D structure of the genome of a small skate (leucoraya erinacea).
They wanted to study skating because the genomes of sharks and rays evolved more slowly than other animals commonly used in research, such as the zebrafish, and resembled the genomes of their ancestral vertebrates. I was. This makes it easier to spot important changes and provides a perspective of genome evolution going back over longer time scales.
Researchers were looking for structures called topology-associated domains (TADs). These are large self-contained loops of DNA and proteins that connect genes to non-coding regions of DNA called enhancers that control when and where the gene is activated.
TADs are known to be involved in development, and structural disruption of TADs can cause congenital diseases in humans. Altered TADs have also been found to drive evolutionary innovation in other mammals, such as the gonads of female moles. The big question is whether they have played a broader role in vertebrate evolution.
The team deduced the 3D structure of Skate TAD and compared it to its closest relative, the shark. They found sections of DNA that split and moved around within the skating TAD containing planar cell polarity genes that help the cells all orient themselves in the same direction within the plane of the tissue. These genes are the reason why all the hairs on mammalian skin point in a certain direction.
The team showed that one of these genes is now involved in the development of skates, but not sharks or pectoral fins. Nakamura suspects this could mean that the cells in her skate fins all stretch in the same direction, affecting tissue shape.
However, this is not the only evolution of skating fins. Other genes and enhancers will be involved, he says. “Evolution is really complicated. It’s more than we expected.”
The researchers found that TADs influence which parts of DNA can be moved or lost and should be kept intact during evolution. “I think it’s a completely different view of how genomes evolve,” says team member Dar.ofo wolfwithout itIt was held at the Max Delbrück Center in Berlin, Germany.
The study demonstrates the power of analyzing and comparing 3D genome structures to uncover new mechanisms behind evolutionary innovation, says Matthew Harris of Harvard Medical School. Rather than looking at how known genes are regulated, using this approach gives us such big surprises. “Nobody would have thought that planar cell polarity was involved in fin evolution,” he says.
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