Scientific career of the sea urchin – will it replace mice and fruit flies?

Against the wall, one on top of the other, stand rows of small plastic tanks. Each holds a sea urchin the size of a pea. Tapes with information about the animal’s genetic modification and the date of fertilization are stuck on all the containers. On some, there is additionally a symbol denoting animals that have modified germ cell DNA, which means they can pass their mutation to their offspring… Is this science fiction? No, it’s the reality of the Scripps Institution of Oceanography at the University of California. What can genetically modified sea urchins bring to science? Will we soon be diving in the ocean with animals mutated by humans!

Sea urchins glowing in the dark

At the end of March 2024, a preprint of the article Stable germline transgenesis using the Minos Tc1/mariner element in the sea urchin, Lytechinus pictus, signed by Elliot W. Jackson, Emilio Romero, Svenja Kling, Yoon Lee, Evan Tjeerdem and Amro Hamdoun, was published on the bioRxivserver. Although the publication is said to be the culmination of five years of work initiated due to overtime at the onset of the SARS-CoV-19 pandemic in a California laboratory, the material promises to be a breakthrough in research from the fields of developmental biology and cell biology.

Instead of fruit flies or mice genetically modified for experiments, scientists will henceforth be able to use genetically modified sea urchins. As proof, the first generation of picture sea urchins(Lytechinus pictus) was presented, which inherited from their genetically modified parents the ability to produce the protein responsible for fluorescence. Do they glow in the dark?

Pictured Hedgehog

Lytechinus pictus (English: painted sea urchin) has not yet earned its Polish name. It lives, unfortunately, far from popular diving sites, on coral reefs of the tropical and subtropical zones of the eastern Pacific Ocean in the coastal belt from California to Ecuador. In the Galapagos or Revillagigedo archipelagos, so popular among Polish divers, there are probably only its close relatives – Lytechinus semituberculatus( green sea urchin). To get a little closer to this interesting animal, let’s try calling it a picture urchin for the purposes of the article.

Pictured sea urchins(Lytechinus pictus) live in fairly dense clusters, near seaweed, from the crowns of reefs to depths as deep as 300 meters. However, the easiest way to encounter them is during a night dive. Their carapaces(test) grow up to 0.4 cm in diameter. They are grayish-brown, with short and blunt spines, bright in the lower part with a palette of purple and pink at the ends. They have been described twice in science, and it was not until 2004, through genetic studies, that Lytechinus pictus (Verrill, 1867)and Lytechinus anamesus (H.L. Clark, 1912)were found to be one and the same species.

Pictured sea urchins(Lytechinus pictus) feed on seaweeds of the genera Laminaria, Gigartina and Macrocystis. They, in turn, are hunted by the colorful starfish Patiria miniata (English: bat star), whose arms look as if they have membranes between them (hence the comparison with a marine bat), and several species of fish, including even one shark. Now one end of this chain is to be firmly grasped by humans.

Why science the sea urchins?

Lytechinus pictus first contributed to science in 1982, together with other sea urchins of the genus Arbacia. Sir Richard Timothy Hunt studied the development of their embryos and, based on this, announced the discovery of cyclins – key proteins that control cell division. He was awarded the Nobel Prize for his discovery in 2001. So what else can sea urchins do for us?

Studies on sea urchins have provided information on the mechanisms of fertilization, cell division and early development. Our common ancestor lived on Earth some 550 million years ago, in the Cambrian ocean, alongside trilobites and anomalocaris. Hedgehogs are evolutionarily close to the base of our animal branch. They belong, along with us, to a clade called the Secondrouste (Deuterostomia) – this means that our rectums form during the embryonic stage before our mouths. At the cellular level, the translation of the protein mixture of the fertilized egg into a developing being still proceeds similarly in sea urchins and humans.

Lytechinus pictus produce huge numbers of eggs and sperm, but fertilization occurs in the water, outside the parent organisms. This allows scientists to observe the creation process on a large scale and up close. Genetically, sea urchins have more in common with humans than fruit flies(Drosophila). The next generation is born in four to six months. It’s downright ideal material for evolutionists. Except that it’s not readily available….

Glowing sea urchins from California

Scientists at the Scripps Institution of Oceanography at the University of California began by sequencing the genome of Lytechinus pictus. This was necessary before attempting any genetic manipulation and developing a system to mass-produce genetically modified sea urchins for laboratory use. In March 2024. demonstrated the possibility of editing sea urchin genes by implanting them with CFP(Cyan Fluorescent Protein), a modified protein based on the famous GFP, the fluorescent protein of the jellyfish Aequorea victoria, for whose discovery Martin Chalfie, Roger Yonchien Tsien and Osamu Shimomura won the 2008 Nobel Prize. Such a protein glows when excited with light of a certain wavelength. Through further mutations, the timing of the glow and its colors were altered.

Today, genetically modified mice are ordered for research in the experimentally required manner. This often provokes protests from people who have the suffering of animals at heart. Can transgenic sea urchins replace them? Hedgehogs are first-rate model organisms for studying the early development of secondaries, but for use in laboratories, the reproduction and growth cycle of most species is too long. Lytechinus pictus has one of the shortest generation periods. The mutant sea urchins from California not only produced a fluorescent protein in their bodies, but also passed this trait on to their offspring.

This shows that the insertion was stable and the mechanism developed works. This gives hope that Lytechinus pictus may become another species of model organisms for various fields of science. Thus, in the near future, scientists may be able to mass-produce sea urchins with specific gene modifications – as is currently the case with fruit flies and mice. Laboratory sea urchins could help in neuroscience, toxicology or developmental biology. They could also facilitate understanding of the mechanisms leading to the evolution of key biological developments, such as the centralized nervous system.

Diving with mutants in open water

And the risks? Powerful populations of invasive wingfish(Pterois volitans and Pterois miles) prowl the Caribbean. These fish are a joy to the eyes when diving in the Indo-Pacific, but they subvert the food ladder by preying on anything that moves, while they themselves are not food for anyone. Genetic studies of captured individuals have shown that the fish are descended from just a few parental organisms that have spread across the reefs of the Gulf of Mexico, the Caribbean Sea and the western Atlantic, taking off off off the coast of Florida.

Legend has it that they escaped from one of the local oceanariums during a hurricane, but officially it is blamed on… aquarists. What if Murphy’s Law works once again and one day transgenic sea urchins make their way into open waters? It’s hard to predict the consequences, but diving among the glowing, invaded spheres may then be the least of our worries….

In the article, I used, among other things. z:

1. Elliot W. Jackson; Emilio Romero; Svenja Kling; Yoon Lee; Evan Tjeerdema; Amro Hamdoun (2024) Stable germline transgenesis using the Minos Tc1/mariner element in the sea urchin, Lytechinus pictus. “bioRxiv” 2024.03.26.586777; DOI: https://doi.org/10.1101/2024.03.26.586777
2. Evans T, Rosenthal ET, Youngblom J, Distel D, Hunt T. (1983) Cyclin: a protein specified by maternal mRNA in sea urchin eggs that is destroyed at each cleavage division. “Cell” 33(2):389-96. DOI: https://doi.org/10.1016/0092-8674(83)90420-8. PMID: 6134587.
3. Petroni G, Formenti SC, Chen-Kiang S, Galluzzi L. (2020) Immunomodulation by anticancer cell cycle inhibitors. ogy” 20(11):669-679. DOI: https://doi.org/10.1038/s41577-020-0300-y. Epub 2020 Apr 28. PMID: 32346095;
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