Lambert, J.D.; Nagy, L.M.: The role of MAPK signaling in patterning mollusc embryos

Classical experiments performed on the embryo of the mollusc Ilyanassa obsoleta demonstrate that the 3D macromere acts as an embryonic organizer, by signaling to other cells and inducing them to assume the correct pattern of cell fates. We have discovered that MAP Kinase (MAPK) signaling is activated in the cells which require the signal from 3D for normal differentiation. Preventing specification of the D quadrant lineage by removing the polar lobe disrupts the pattern of MAPK activation, as does ablation of the 3D macromere itself. Blocking MAPK activation with the MAPKK inhibitor U0126 produces larvae which differentiate the same limited complement of tissues as D quadrant deletions. Our results suggest that the MAPK signaling cascade transduces the inductive signal from 3D and specifies cell fate among the cells that receive the signal. We also report the pattern of MAPK activation in other mollusc embryos, and discuss the implications for the evolution of axial patterning in this group.