Location, location, location

Scientists working on how the part of the fruit fly brain that processes visual information develops have offered a new model to explain how neural stem cells produce multiple types of neurons.

Their investigation into the neurogenesis of the optic lobe, published earlier in Nature, shows that alongside temporal patterning, where stem cells produce sequentially different types of neurons as they age, stem cell location adds to this diversification¹.

The fruit fly optic lobe is formed of four neuronal structures. The medulla, responsible for processing motion and colour vision, is the largest of these. Organised into repetitive columnar units of cells, the medulla contains over 80 types of neuron. Around 20 are unicolumnar — they process information about an individual pixel through a single column. They are known to form through a combination of temporal and notch patterning mechanisms. But in the remaining 60 multi-columnar types, where the neuron spreads over multiple columns to compare information from larger visual fields, little was understood of cell formation.

Researchers at New York University’s Department of Biology, NYU Abu Dhabi and the Universities of Chicago and Toronto, found that the crescent shaped neuroepithelium from which medulla develops is subdivided into six compartments along the dorsal and ventral axis by the expression of specific transcription factors.

“The same temporal patterning produces different neurons depending on where the stem cell comes from,” says lead author Claude Desplan, NYU. Uni-columnar neuron types are produced in all of the compartments at a given temporal stage. However, multi-columnar neuron types are produced in restricted regional domains. 

“It is a combination of temporal and spatial patterning that generates diversity,” says Desplan. “We hope that vertebrate people will take these concepts and apply them to understanding patterning of the vertebrate retina or cortex.”

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