How Cell Death in the Nervous System Leads to Zombie Neurons

A new study, conducted in fruit flies (Drosophila melanogaster), has found that by stopping the death of neurons during brain growth they later develop new networks of neurons, with roles and properties that are not identical to those of existing neurons.

The researchers genetically inhibited the last stage of apoptosis in neurons of the fly olfactory system. They found that the rescued 'zombie' cells, which would have otherwise been destroyed, developed into functioning olfactory neurons that were able to detect smells. However, the 'zombie' neurons expressed different olfactory receptors than their standard counterparts.

For example, some of the 'zombie' neurons found in an olfactory organ called the maxillary palp had receptors to detect carbon dioxide, a cue used by insects to sense the presence of animals and humans, as these exhale carbon dioxide when breathing. These extra neurons gave the flies similar characteristics to mosquitos (Anopheles gambiae), which, unlike flies, also have carbon dioxide-sensing olfactory neurons in their maxillary palps.

"When the neurons that normally die were protected from apoptosis they developed into 'zombie' neurons that have similar characteristics as certain neurons in mosquitos. Apoptosis therefore is one factor responsible for how mosquitos and fruit flies have adapted over time to their different environments," said Lucia Prieto-Godino, co-first author of a paper published today in Science Advances.

"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," added Richard Benton, senior author.