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For the first time, researchers at Umeå University have observed the same type of programmed cell death in microalgae as in humans. The discovery, in Nature Communications, shows that this central biological process is older than previously thought.

"This is the first photosynthetic organism, and the first single-cell organism, shown to produce so-called apoptotic bodies during cell death. This proves that apoptosis, a pathway of programmed cell death which was thought to be unique to animals, is more ancient and widespread than previously believed," says Christiane Funk, professor at the Department of Chemistry, Umeå University.

Cells can die naturally from age or disease, but organisms can also actively trigger the death of certain cells when needed. This is known as programmed cell death (PCD), a central biological system that allows the development of organs in our bodies and provides advantage during an organism's life cycle. One example is the differentiation of fingers in a developing human embryo, others are the control of cell numbers or the elimination of nonfunctional cells.

There are several pathways leading to PCD, the best studied being apoptosis. The clearest sign of apoptosis is the formation and release of membrane-enclosed extracellular vesicles called apoptotic bodies. Although other pathways have been described in plants, yeast, protozoa and phytoplankton, the production of apoptotic bodies has been thought to be limited to multicellular animals.

For the first time, Funk's group at Umeå University has now been able to observe the formation of apoptotic bodies in microalgae.

"Our results demonstrate that the microalga Guillardia theta experiences apoptotic cell death in physiological conditions, similar to animal cells. Since these algae already existed prior to the origin of multicellularity, our discovery questions the evolutionary origin of PCD," says Funk.

The new findings may also have long-term implications beyond basic research. If scientists could one day induce or prevent programmed cell death in microorganisms, it might be possible to both manage harmful algal blooms and improve the harvesting of algal products in biotechnology. "But this is still far ahead of our current study," says Funk.