- Retinoic acid signalling in the zebrafish embryo is necessary during pre-segmentation stages to pattern the anterior-posterior axis of the CNS and to induce a pectoral fin bud. Grandel, H., Lun, K., Rauch, G.J., Rhinn, M., Piotrowski, T., Houart, C., Sordino, P., Küchler, A.M., Schulte-Merker, S., Geisler, R., Holder, N., Wilson, S.W., Brand, M. Development (2002)