According to research conducted in fruit flies at the Francis Crick Institute, the University of Lausanne (UNIL) and the Max Planck Institute for Chemical Ecology, zombie cells tend to develop into functional neurons when the death of neurons is stopped during brain growth.
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When the brain develops, a large number of neurons undergo self-destruction as part of a vital regulatory mechanism, eliminating the surplus cells. In specific sections of the human brain, 50% of neurons get affected as the cells kill themselves by a process called apoptosis.
This study was performed in fruit flies—Drosophila melanogaster—and discovered that when the death of these cells is prevented, they develop into new networks of neurons, the roles, and properties of which differ from that of the existing neurons. The study was reported in Science Advances.
The final stage of apoptosis in neurons of the fly olfactory system was genetically inhibited by the researchers. They identified that the rescued “zombie” cells, which would have been killed otherwise, in fact, developed into functional olfactory neurons with the ability to detect the smell. But the zombie neurons expressed different types of olfactory receptors compared to their standard counterparts.
For instance, a few of the “zombie” neurons that exist in an olfactory organ, known as maxillary palp, consisted of receptors to detect carbon dioxide—a prompt that insects use to sense the presence of humans and animals, as they breathe out carbon dioxide.
These additional neurons provided the flies with characteristics similar to that of the mosquitoes (Anopheles gambiae), which are not like flies and have carbon dioxide-sensing olfactory neurons in their maxillary palps. Both species have a common ancestor that lived nearly 250 million years ago.
When the neurons that normally die were protected from apoptosis they developed into ‘zombie’ neurons that have similar characteristics as certain neurons in mosquitoes. Apoptosis therefore is one factor responsible for how mosquitoes and fruit flies have adapted over time to their different environments.”
Lucia Prieto Godino, Study Co-First Author and Group Leader, Neural Circuits and Evolution Laboratory, Francis Crick Institute
According to Richard Benton, senior author and group leader at the Center for Integrative Genomics at UNIL, “From an evolutionary point of view, our results suggest that changes in patterns of cell death in the nervous system could allow a species to adapt to new pressures from its environment, by enabling the evolution of new populations of neurons with novel structural and functional properties.”
Although the researchers did not perform an in-depth study of the behavior of flies with additional olfactory neurons, the increase in the number of neurons theoretically enables them to sense odors with higher sensitivity.
This could have a crucial role in enabling the flies to find a partner, food, or danger coming, thereby being beneficial when compared to other individuals.