How do cells form organs? That is, how does each cell within an organ assume the correct shape and form the right contacts with its neighbors?
Those are the questions that interest Max Heiman, a postdoc in Shai Shaham's lab at the Rockefeller University in New York, who earlier this year showed how two proteins shape the neurons and glia of the C. elegans sensory organ. The two proteins - DEX-1 and DYF-7 - anchor the neuronal dendrites at the nose of the worm while the cell body migrates away, eventually forming an axon that projects into the worm brain. Both proteins are secreted, and seem to form an extracellular matrix that prevents the dendrite from being dragged away with the cell body, helping the neurons form their correct, elongated shape. Heiman has now extended this work by asking whether other worm neurons similarly depend on DEX-1 and DYF-7. The answer is no - but he's identified mutants that specifically affect other groups of neurons instead. Different neurons therefore seem to use distinct machinery to form their correct contacts and shape. Especially intriguing is Heiman's idea that components of the extracellular matrix can play specific roles in shaping cells - it's rather like guy ropes giving shape to a tent in addition to the internal framework provided by tent poles.
Image of a worm sensory neuron from Evans et al, J Cell Biol, 2006.
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