Holothuria tubulosa, a Mediterranean sea cucumber, has been established as a new model organism, promising advances in genetic research and conservation efforts.
Scientists utilize a handful of standard research organisms, including fruit flies and mice, to study the evolutionary development (evo-devo) of animal lineages. Expanding the variety of these research organisms enhances our understanding of life and advances biomedicine and ecological conservation.
In a recent study, published in Frontiers in Evolutionary Developmental Biology, scientists from the Marine Biological Laboratory (MBL) in Woods Elven and the Stazione Zoologica Anton Dohrn (SZS) in Naples, Italy, have introduced the sea cucumber species Holothuria tubulosa as a new evo-devo research organism.
Benefits of Using Echinoderms
Found in the Mediterranean Sea and the eastern Atlantic Ocean, Holothuria tubulosa belongs to the echinoderm group, which includes sea urchins, sea stars, and sand dollars. Some species of echinoderms have been used in developmental studies for over a century due to their cost-effectiveness, high fecundity, clear larvae, and recently, suitability for genetic research.
“Echinoderms are the closest invertebrates to humans genetically, which means we have most of our genes in common. If we understand how those genes function in an echinoderm, than we also know how they function in humans,” said Margherita Perillo, a research scientist at MBL who led the study.
“Sea cucumbers also have attributes and special skills — such as being deposit feeders, which cleans the ocean floor, and the ability to completely regenerate their whole body — that could be useful in conservation and biomedicine,” she added.
Larva of the sea cucumber, Holothuria tubulosa, showing nuclei (cyan) and actin (magenta). Credit: Perillo et al, Front. Ecol. Evol. 2024
Protocol for Producing Embryonic Cultures
The first step in establishing H. tubulosa as a research organism was to develop a protocol to efficiently produce embryonic cultures in a lab setting. Existing methods, including mimicking the animal’s natural breeding cycle and inducing the release of all the animal’s organs by evisceration (a behavior that sea cucumbers normally exhibit when threatened) were complicated, inefficient, or both.
To overcome this, the research team led by Rossella Annunziata from SZS and Perillo pioneered a noninvasive technique to repeatedly harvest a small number of gametes (sperm and eggs) over a long period of time. The microsurgery involves a small incision near a sea cucumber’s reproductive organs, allowing for the retrieval of testes or ovaries. The incision heals quickly and gives researchers the ability to harvest every few days from the same animal.
Since eggs retrieved using this technique have not reached maturation and cannot be fertilized, the researchers next expose the harvested ovaries to a synthetic peptide – Thioredoxin-2 peptide, known to work in another species – to make them receptive to sperm. They then grow the fertilized egg in a culture, where it reaches the metamorphosis stage in about eight weeks.
Perillo explains, “Our protocol removes a major bottleneck that has kept H. tubulosa from being used as a research organism and opens the door for more scientists to use it.”
The sea cucumber Holothuria tubulosa eviscerating its organs, including ovaries (orange). Credit: Perillo et al, Front. Ecol. Evol. 2024
Advancements and Future Prospects
The team used high-resolution microscopy coupled with immunohistochemistry to document the development of the larvae, with a focus on its unique structures. Their detailed description will serve as a foundation for future studies that aim to use genetic manipulations to functionally dissect development in H. tubulosa.
Additionally, they provided an example of how scientists can use echinoderm larvae to study the diversification of anatomical structures in closely related organisms. In this case, they used serotonin immunostaining to show how the location of serotonin neurons differed between types of echinoderms. Why and how this diversification occurs is an open question in evolutionary development biology.
“The sea cucumber is a fascinating animal and the better we understand it, the more value it has as a research organism,” said Perillo. “My plan now is to develop genetic tools to help further characterize it as an emerging comparison model in evo-devo. At the same time, this collaborative work laid the foundation to establish a new sea cucumber species here at the MBL.”
Reference: “Larval development of Holothuria tubulosa, a new tractable system for evo-devo” by Margherita Perillo, Tanya Alessandro, Alfonso Toscano and Rossella Annunziata, 6 May 2024, Frontiers in Ecology and Evolution.
DOI: 10.3389/fevo.2024.1409174
Perillo received an Emerging Research Organisms grants from the Society of Developmental Biology to support her work and to continue her study of H. tubulosa.
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