Research suggests that multicellularity has evolved at least 45 times throughout the tree of life. The ancestors of every modern multicellular lineage relied on only one of two methods: single cells that stuck together when they divided, or single cells that had previously divided and then come together again.
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Clonal polycytosis, in which cells remain connected as they divide, has given rise to organisms as simple as cyanobacteria and as complex as animals with their specialized tissues. Another type of multicellularity, called aggregation, is the temporary assembly of free cells that occurs when slime molds and amoebae cooperate, often in response to harsh environmental conditions or predation.
Scientists from the Pasteur Institute led by Nuria Ross Rocher Researchers made a surprising discovery while studying dinoflagellates: single-celled organisms that live in water, form short-lived colonies, and are the closest living relatives of single-celled animals.
These multicellular organisms behave in unusual ways
Scientists have observed the behavior of dinoflagellates Choanoica flexa. This species creates stunning colonies that resemble exploding fireworks, which may help us better understand gastrulation, a key stage of embryonic development. Dinoflagellates formed colonies through cell division, causing them to multiply and increase in numbers. It is no wonder that scientists observed cell division in the colonies C. Flexaany It was first discovered in 2018 In swimming pools on the rocky coast of the Caribbean island of Curaçao.
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But under the microscope, they behaved unusually. It turned out to be colonies C. Flexa They regenerated very quickly after disintegration under the influence of light – too quickly to be converted into cell division. When fluorescent dyes were used to stain different types of cells C. FlexaScientists saw distinct groups of single cells forming chimeric (double-labeled) populations, which would not be possible if they came from the same founder cell.
Scientists initially doubted their observations because they seemed too strange to be true. Subsequent experiments showed this C. Flexa They can aggregate in single-layer plate-like colonies (e.g. slime molds) or develop clonally (e.g. animals).
Dr. Thibaut Brunet of the Pasteur Institute says:
We found that C. flexa clades can be formed by purely clonal processes, purely combinatorial processes, or a combination of them, depending on the experimental conditions. Using two mechanisms simultaneously – mechanisms that are often presented as mutually exclusive – is likely to allow faster evolution.
Further experiments revealed a multicellular form C. Flexa It depends on the conditions in the shallow seawater pools where the organisms are found. When the salinity of these ponds exceeded the critical limit and tripled as seawater evaporated, the colonies began to multiply. C. Flexa They have separated into individual sac-like cells to prevent drying out. After rehydration in the laboratory C. Flexa Colonies were fixed within days, first pooled and then divided.
Although the study has not yet been peer-reviewed, it has been posted on a preprint server com.bioRxiv It may indicate a previously unknown life cycle related to the environment. This may change our perception of multicellularity and our understanding of basic biological processes.
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