aAs fog drifts over a Swedish fjord lined with towering forested cliffs, a group of scientists collects mud from the bottom of turquoise water. They are targeting spider stars, marine animals with long, slender, snake-like arms, and studying the genes that give them their unique characteristics, such as their ability to regenerate.
Spider stars belong to the phylum Echinoderm, which also includes starfish, sea urchins, sea cucumbers, and crinoids. on the other hand, genome Of these other echinoderm class It is characterized, Ferdinand Marletas“Surprisingly, there was no genome available,” said the evolutionary biologist at University College London. [for brittle stars]”1-4
To study this interesting creature, Marletas’ team collected hundreds of spider stars from Swedish fjords and returned to the lab to sequence the spider star’s genome. marine animals, belonging to a species Amphiura filiformis.5 The result is natural ecology and evolutionreveals how amphiulids have evolved and provides insight into the genes involved in limb regeneration.
“This is a huge resource,” he said Mansi SrivastavaHe is an evolutionary and developmental biologist at Harvard University but was not involved in the study. “It will advance a question that many in evolutionary developmental biology have.”
Marletas’ team extracted and sequenced the DNA collected from the spider star and assembled the genome. To map how spider stars have evolved since they diverged from other echinoderms about 500 million years ago, the research team A. filaformis The genomes are the same as those of sea urchins, starfish, and sea cucumbers. They observed that the spider star’s genome has undergone greater genetic changes compared to other echinoderms, including shuffling of genes across chromosomes. Among the rearranged genes were genes in the Hox cluster, which shapes the animal’s body plan. These genes are same order They are located on the same chromosome in evolutionarily distant animals.6 Genes within Hox clusters of other echinoderms showed this expected order, but genes within the spider star genome broke this pattern.
“[This was] This is surprising since Hox clusters are known to be very conservative with respect to gene order. ” Elise Parayan evolutionary biologist at University College London and co-author of the study.
Srivastava noted that studying this rearrangement could provide important insights into the role of this gene cluster in echinoderms. “Hox genes seem to have a lot of constraints throughout evolution,” Srivastava says. “So here’s an animal that played with that constraint. So when you study something that deviates from the rule, you can actually learn something more about the rule,” she explained. .
With the spider star’s genome in hand, Marletas and his team investigated another important characteristic of the animal: its ability to regenerate. Like many other echinoderms, spider stars also regenerate limbs After the amputation.7 “Spider stars can regrow their arms in just a month, which is extremely fast,” Parry said. By comparison, starfish can take up to several months to regrow lost arms, making spider stars an important model for studying the genes involved in regeneration.
Marletas and his team sought to identify the genes underlying such regenerative powers. They cut off the arms of about 3,500 animals and assessed gene expression as the arms regenerated. As regeneration progressed, different genes emerged as important mediators. Genes involved in the wound response, including immune and cell migration-related functions, are activated during the early stages of regeneration, whereas later stages are characterized by increased activity of genes associated with tissue differentiation and limb formation.
Mapping the ancestry of these genes revealed that the expression of ancient genes is significantly involved in arm regeneration, indicating that genetic roots are shared among other regenerating animals. . To investigate whether similar genes are involved in limb regeneration in other animals, the researchers looked at genes expressed during regeneration between distantly related species. They compared the genetic profile of the spider star to that of two other previously published regenerating animals, the axolotl (Mexican Ambystoma) and marine crustaceans (Palyare hawaiensis). They observed that all three animals expressed similar genes during limb regeneration, validating a common ancestral origin of regeneration.
“Our paper is probably one of the few that attempts to compare genes involved in regeneration processes across lineages,” Marletas said.
“This is a paper that calls for us to study more species with this comparative method,” agreed Srivastava. But she says identifying the spider star’s genes is the first step. “You have to do some functional work on the bench to actually ask what they’re doing.”
Parai agreed. ” [next steps] This will be a biological validation experiment to investigate the role of specific genes in detail. ”
