In addition to encountering a different cellular substrate, the axons also encounter distinct basement membranes. It is speculated that the unique appearance and trajectories of these axons are because they are simultaneously directed dorsally by UNC-6DeltaC, despsite being inhibited from migrating across the lateral epidermis by cues associated with the lateral body wall. This further suggests that the motoneuron axons that normally migrate circumferentially have specific properties that allow them to migrate to the dorsal midline. UNC-6DeltaC acts as an antagonist to the action of domain C at the ventral nerve cord. Finally, these results provide evidence that in vivo the influence of guidance cues can be modified locally to alter axon trajectories.
Cell migrations play a critical role in animal development and organogenesis.
Here, a mechanism is described by which the migration behaviour of a particular cell type is regulated temporally and coordinated with over-all development of the organism. A single amphioxus netrin gene was isolated by PCR and cDNA library screening and named AmphiNetrin . The predicted AmphiNetrin protein shows high identity to other netrin family members but differ in that the third of three EGF repeats found in other netrins is absent. Despite the absent EGF repeat AmphiNetrin is most closely related to the vertebrate netrins. AmphiNetrin is expressed in embryonic notochord and floor plate, a pattern similar to that of vertebrate netrin-1 expression.