Turning Blood into Brains

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When you think crayfish, you probably think of food rather than groundbreaking medical research, but a paper published last month in Developmental Cell reports an incredible neurological feature of the humble lobster. Stem cells, blueprint cells that produce new cells, are vital for repairing wear-and-tear. Research from the US revealed a remarkable talent in Crayfish – they can grow new brain stem cells from their blood.

We are constantly replacing most of the cells in our body. Cells die, and new ones are generated from stem cells. The neurons in our brain are no different, and humans have the capacity, albeit limited, to replace damaged brain cells. But only from neural stem cells. Crayfish, on the otherhand, appear to be converting blood cells into neurons to regenerate their senses. The new neurons are used to replace damaged cells in their eyestalks and in the brain cells that deal with olfactory signals – smell.

BloodBrains002Olfactory nerves are often damaged and have been found to naturally regenerate in fruit flies, crustaceans and humans. The process begins with the niche, and small region at the base of the brain that acts as a nursery for new neurones. In crayfish, blood cells are attracted to the niche where they divide into two neuron-precursor cells and migrate to the olfactory system, replacing damaged neurons and preventing the crayfish losing their sense of smell.

Scientists began to suspect something was up when they saw that the crayfish seem to have a never-ending supply of neuron-precursor cells. No matter how many you used up, they just kept finding more. The recent research by Professor Barbara Beltz and colleagues at Wellesley college, Massachusettes, showed that blood cells called haemocytes are attracted to the niche, revealing the source of the infinite neuron-precursors.

Using a chemical that controls the production of haemocyes, Beltz showed that the more haemocytes available, the more neuron-precursor cells a crayfish has. Next, Beltz and her team transplanted haemocytes, labelled with a DNA dye, from one crayfish to another. Just a week later, these labelled cells arrived at the olfactory clusters to become neurones. Two months later, they were ready to start work producing their own neurotransmitters and communicating olfactory signals in the brain.

Neurogenesis in the crayfish brain during hatching.
Sintoni et al (2012) Neurogenesis in the central olfactory pathway of adult decapod crustaceans: development of the neurogenic niche in the brains of procambarid crayfish Neural Development

It is hoped this discovery will pave the way for neurological stem cell research. Although the process by which haemocytes are reprogrammed as neurons is currently unknown, further research could provide important data for stem cell therapies for patients with neurological damage. Regenerating neurones is a key area of research in the effort to treat and cure Parkinson’s disease. Crayfish stem cells are similar to humans, except for one key difference – human stem cells normally regenerate themselves, with one daughter cells from each division remaining behind as a stem cell. In crayfish, both stem cells differentiate into olfactory nerves, which may explain the need to recruit new stem cells from the blood.

Reprogramming cells could have enormous implications for medicine, and researchers in Kyoto have previously succeeded in reprogramming skin cells into embryonic stem cells. Crayfish, however, are the first example of this process occurring in nature, rather than the lab.

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Featured image used under a creative commons licence from wikimedia commons. Original image by Robert M Hunt

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