An international research team has found that the bodies of starfish and other echinoderms are nothing more than heads without bodies. According to the press release published on the “Eurek Alert” website, the research published on November 1 in the journal “Nature” helps answer the mystery of how these creatures acquired their distinctive star-shaped body, which has puzzled scientists for a long time.
Compare gene expression
Echinoderms are a group of animals that include sea stars, sea urchins, and sand dollars. They have a unique body structure that causes their body parts to be arranged in 5 equal sections. This is quite different from other bilateral organisms that have a right and left side that mirror each other, as is the case in humans and many other animals.
“How the different body parts in echinoderms relate to those seen in other groups of animals has been a mystery to scientists throughout their study, whereas in bilateral organisms the body is divided into a head, trunk and tail,” said study co-author Dr Geoff Thompson from the University of Southampton.
In the new study – led by Laurent Formery and Professor Chris Lowe at Stanford University – scientists compared the molecular markers of starfish with other deuterostomes, a broader animal group that includes echinoderms and bilateral animals, such as vertebrates.
Advanced study techniques
The researchers used a variety of high-tech molecular and genomic techniques to understand where different genes are expressed during the development and growth of sea stars. The team in Southampton also used computed tomography to understand the shape and structure of the animal in unprecedented detail.
The researchers at Stanford University, in collaboration with Professor Dan Rokhsar at the University of California, Berkeley, and the Pacific Biosciences Foundation, then used RNA tomography to create a 3D map of gene expression in starfish and see where specific genes were located.
Specifically, the researchers mapped the expression of genes that control the development of the ectoderm that includes the nervous system and skin. This is known to represent the anteroposterior (front to back) pattern in other deuterostomes.
They found that this pattern was related to the medial to lateral axis of the starfish’s arms, with the middle line of the arm representing the front part, and the extreme lateral parts more like the back. As for deuterostomes, there is a distinct set of genes expressed in the ectoderm of the trunk. But in starfish many of these genes are not expressed in the ectoderm at all.
Echinoderms: heads without bodies
Dr. Thompson explains that when they compared gene expression in the starfish with other groups of animals, such as vertebrates, it seemed to them that an important part of the body plan was missing. The genes that are normally involved in the formation of the animal’s torso were not expressed in the ectoderm of the starfish, and it seemed that the body plan The entire echinoderm is roughly equivalent to the head in other groups of animals.
This suggests that sea stars and other echinoderms may have evolved their 5-segmented body plan through the loss of the trunk region found in diploids, and this would allow echinoderms to move and feed differently than diploids.
“Our research tells us that the body plan of echinoderms evolved in a more complex way than we previously thought, and there is still a lot to learn about these interesting creatures,” says Dr. Thompson.