The nerve ring - the most anterior axon bundle in C. elegans - is derived from over half of the animal's neurons and is regarded as the animal's brain. Now, on , Cornelia Bargmann and co-workers report that Wnt signalling through a Ror tyrosine kinase homologue directs the development of this primitive brain. The researchers identify cwn-2, the C. elegans homologue of Wnt5, as a regulator of nerve ring placement in a genetic screen. They report that cwn-2, which is expressed in cells posterior to the nerve ring, acts mainly through CAM-1, the C. elegans Ror2 homologue, an unexpected result given that CAM-1 is a non-signalling receptor in other C. elegans Wnt signalling pathways. Other experiments show that the SIA and SIB neurons, which lie near the base of the nerve ring, play a crucial role in positioning the nerve ring. The researchers suggest, therefore, that cwn-2 directly affects axon guidance of the SIA and SIB neurons, which then organize the nerve ring.
