Hartfuss, E., Förster, E., Bock, H. H., Hack, M. A., Leprince, P.,Luque, J. M., Herz, J., Frotscher, M. and Götz, M. Development130, 4597-4609.

The authors wish to add the following to their acknowledgements.

J.M.L. was supported by Ministerio de Ciencia y Tecnologia Grant BFI 2001-1504 to Alfonso Fairen.

We apologise to readers for this omission.