WNT3A and melanoma: To test whether the infiltration of single melanoma cells from aggregates observed in the neural crest or the rhombencephalon could be reproduced in a similar 3D–environment in vitro, we embedded SKMEL28 melanoma cell aggregates into a collagen matrix with or without 3T3 cells or Wnt3a secreting 3T3-Wnt3a cells as stroma.