MAPK signaling by the D quadrant embryonic organizer of the mollusc Ilyanassa obsoleta

Classical experiments performed on the embryo of the mollusc Ilyanassa obso leta demonstrate that the 3D macromere acts as an embryonic organizer, by s ignaling to other cells and inducing them to assume the correct pattern of cell fates. We have discovered that MAP kinase signaling is activated in th e cells that require the signal from 3D for normal differentiation. Prevent ing specification of the D quadrant lineage by removing the polar lobe disr upts the pattern of MAPK activation, as does ablation of the 3D macromere i tself. Blocking MAPK activation with the MAP Kinase inhibitor U0126 produce s larvae that differentiate the same limited complement of tissues as D qua drant deletions. Our results suggest that the MAP Kinase signaling cascade transduces the inductive signal from 3D and specifies cell fate among the c ells that receive the signal.