Remarkable migration
To test what happens to the blood, she used a chemical called astakine 1, which controls the production of haemocytes, to tweak the number that were coursing around live animals. This, she found, also changed the number of cells in the niche. And more haemocytes meant more baby neurons.
Beltz's team then extracted haemocytes from "donor" crayfish, labelled them with a DNA dye and pumped them back into different "receptor" crayfish. Three days after transfusion, the label showed up in cells in the niche. Seven days later it was at the base of clusters 9 and 10. And seven weeks after transfusion the labelled cells were producing neurotransmitters, the chemicals that neurons use to communicate with each other.
Exactly how the blood cells are reprogrammed to become brain cells is a mystery, but understanding the mechanism could help us devise new therapies to reprogram human cells, says Beltz.
"The study is very thorough," says Chris Mason of University College London. It shows that two cell systems that are normally thought to be completely separate – cells that make blood and cells that make neurons – can cross over.
How to regenerate neurons is a key question for those studying neurodegenerative conditions like Parkinson's disease. Several groups try to persuade stem cells to turn into neurons, and Beltz points out that the precursor neurons in crayfish are similar to human stem cells with the exception that the human versions self-regenerate. In humans, after a stem cell splits in two, only one of the daughter cells migrates away and differentiates into a specialised cell, leaving one behind to produce more daughter cells.