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Exploring diversity in cell division

Cell division is one of the vital fundamental processes of life. From bacteria to blue whales, every organism on Earth relies on cell division for growth, reproduction, and species survival. Yet, there’s considerable diversity in the best way different organisms perform this universal process. A recent study by the Dey group at EMBL Heidelberg and colleagues, published recently, explores how different methods of cell division evolved in fungi and shut animal relatives, for the primary time. By showing that there’s a relationship between the life cycle of an organism and their mechanisms. Cells divide.

Despite last sharing a typical ancestor a billion years ago, animals and fungi are similar in some ways. Both belong to a broad group called 'eukaryotes' — organisms whose cells store their genetic material in a sealed compartment called a 'nucleus'. However, the 2 differ in how they perform many physiological processes, including probably the most common sort of cell division — mitosis.

Most animal cells undergo 'open' mitosis, through which the nuclear envelope — the two-layered membrane that separates the nucleus from the remainder of the cell — breaks down because the cell begins to divide. However, most fungi use a unique type of cell division — called 'closed' mitosis — through which the nuclear envelope stays intact throughout the division process. However, little is thought about why or how these two distinct modes of cell division evolved and what aspects determine which mode will likely be adopted primarily by a specific species.

This query caught the eye of scientists from the Dey group at EMBL Heidelberg, who investigate the evolutionary origins of the nucleus and cell division. “By studying diversity in organisms and reconstructing how things evolve, we can begin to ask whether there are universal principles that govern how things evolve,” said Gautham Dey, group leader at EMBL Heidelberg. indicate how such basic biological processes work.”

In 2020, throughout the COVID-19 lockdown, an unexpected solution to answer this query emerged from a conversation between Dey's group and Omaya Dudin's team on the Swiss Federal Institute of Technology (EPFL), Lausanne. Duden makes a speciality of an unusual group of marine protists – the Ichthyosporea. Ichthyosporea are closely related to each fungi and animals, with different species being closer to at least one group or the opposite on the evolutionary family tree.

The Dey and Dudin groups, along with Yannick Schwab's group at EMBL Heidelberg, decided to analyze the origins of open and closed mitosis using Ichthyosporea as a model. Interestingly, the researchers found that some species of Ichthyosporea undergo closed mitosis while others undergo open mitosis. Therefore, by comparing and contrasting their organisms, they will gain insight into how organisms adapt and use these two cell division methods.

Harel Shah, an EIPOD Fellow working in all three groups, led the study. “Having soon recognized that the Ichthyosporea, with their many nuclei and key evolutionary position between animals and fungi, were well suited to address this question, it was clear that Dey, Dudin's cell Biological and technical expertise will need to be brought together, and the Schwab groups, and that's exactly what the EIPOD fellowship allowed me to do,” said Shah.

After closely examining the cell division mechanism in two species of ichthyosporeans, the researchers found that one species favors closed mitosis, much like that of fungi. There can be a life cycle with a multinucleate stage, where many nuclei are present inside a single cell — one other feature shared by many fungal species in addition to the embryonic stages of some animals, akin to Fruit fly. Another species, counting on open mitosis, turned out to be very animal-like. Its life cycle consists primarily of mononucleate stages, where each cell has a single nucleus.

“Our findings provide the key conclusion that the way animal cells perform mitosis evolved millions of years before animals. This work therefore has a direct impact on our general understanding of how eukaryotic cell division mechanisms work.” Diverse life evolves and diverges within the context of life cycles, and provides a vital piece of the animal origin puzzle,” said Dee.

The study used comparative phylogenetics, electron microscopy (from the Schwab Group and the Electron Microscopy Core Facility (EMCF) at EMBL Heidelberg), and ultrastructure expansion microscopy, a method that involves embedding biological samples in a transparent Xpan gel and Physically involved. Additionally, Eelco Tromer, from the University of Groningen within the Netherlands, and Iva Tolic, Ru?er Boškovi? The institute in Zagreb, Croatia provided expertise in comparative genomics and mitotic spindle geometry and biophysics, respectively.

“The first time we saw an enlarged nucleus, we knew this technique would change the way we study the cell biology of non-model organisms,” said Shah, who joined EMBL after a stint within the Davidon lab. Brought the strategy of magnification microscopy back to Heidelberg. . Dey agrees: “A major breakthrough in this study came with our analysis of the ichthyosporan cytoskeleton by ultrastructure expansion microscopy (U-ExM). Without U-ExM, immunofluorescence and most dye-labeling protocols would Marine Holozoans do not work in the studied group.”

This study also demonstrates the importance of moving beyond traditional model organism research when attempting to reply broad biological questions, and further research on ichthyosporean systems may reveal potential insights. “Ichthyosporan development shows remarkable diversity,” Dudin said. “On the one hand, many species exhibit developmental patterns similar to early insect embryos, including multinucleated stages and synchronized cellularization. On the other hand, cleavage divides, breaks symmetry, and differentiates into different cell types. together form multicellular colonies, as 'This diversity of early animal embryos not only helps to understand the animal pathway but also provides an interesting opportunity for comparative embryology outside of animals, which itself Very interesting.”

The inherent interdisciplinarity of the project served as test not just for any such collaborative research, but additionally for the unique postdoctoral training provided at EMBL. “Heral's project illustrates well the quality of the EIPOD program: a truly interdisciplinary project, combining modern biology with modern methods, all of which contribute to a truly wonderful personal development,” said Schwab. Schwab said. “We (as mentors) witnessed the birth of a strong scientist, and it's really rewarding!”

The Dey, Dudin, and Schwab groups are also currently collaborating on the PlanExM project, which is a component of the TREC campaign — an EMBL-led initiative to explore and sample biodiversity along European coasts. PlanExM goals to use magnification microscopy to review the ultrastructural diversity of marine protists directly in environmental samples. “This project grew out of the realization that U-ExM would be a game-changer for proteotology and marine microbiology,” Dee said. With this project, together with other work currently underway, the research team hopes to shed more light on the variety of life on Earth and the evolution of basic biological processes.