Invadosomes: aiding axonal invasion

Invasive cells such as immune and metastatic cancer cells form protrusions known as invadosomes, which mediate adhesion to the underlying substrate and induce extracellular matrix degradation – thus promoting invasiveness. On p. 486, Timothy Gomez and colleagues demonstrate that invadosomes can also be found in axon growth cones, where they have not previously been characterised. Primarily using Xenopus spinal cord neurons as a model, the authors use high-resolution imaging techniques to identify and characterise these structures, both in culture and in vivo. Importantly, similar structures can be found in other Xenopus neuron populations, as well as neurons derived from human pluripotent stem cells. In functional assays, the authors find that axon growth in culture is unimpeded by disruption of the invadosome protein Tks5, but in vivo outgrowth of motoneurons into the periphery does require invadosome activity. Thus, these data not only demonstrate the presence of invadosomes in growth cones, but also provide evidence for a specific role for these structures during certain phases of axon outgrowth.