Directional cell migration in vivo: Wnt at the crest

Directional cell migration is essential for almost all organisms during embryonic development, in adult life and contributes to pathological conditions. This is particularly critical during embryogenesis where it is essential that cells end up in their correct, precise locations in order to build a normal embryo. Many cells have solved this problem by following a gradient of a chemoattractant usually secreted by their target tissues. Our recent research has found an alternative, complimentary, mechanism where intracellular signals are able to generate cell polarity and directional migration in absence of any external chemoattactant. We used neural crest cells to study cell migration in vivo, by performing live imagining of the neural crest cell migrating during embryo development. We show that the Planar Cell Polarity (PCP) or non-canonical Wnt signaling pathway interacts with the proteoglycan syndecan-4 to control the direction in which cell protrusions are generated, and in consequence, the direction of migration. By analyzing the activity of the small GTPases using in vivo FRET imaging we showed that PCP signaling activates RhoA, while syndecan-4 inhibits Rac, both at the back of the neural crest cell. Here we discuss a model where these signals are integrated to generate directional migration in vivo.