TERATOGENIC AND MORPHOGENETIC EFFECTS OF RETINOIC ACID ON THE REGENERATING PECTORAL FIN IN ZEBRAFISH

Following amputation, the pectoral fin undergoes a regenerative process which leads to an apparently faithful replacement, both in shape and in size, of the missing part. However, analysis of the fin skeleton in whole mount preparations of normal and regenerated fins has revealed that fin regenerates are not perfect copies of the missing part, and that the distance and the number of ray segments between the amputation plane and the first dichotomy are higher in regenerated than in unamputated fins. This suggests that a respecification of positional values may be induced by amputation. Since retinoic acid (RA) induces duplication of structures in the regenerating amphibian limb, and affects pattern formation in the zebrafish nervous system, we have investigated whether RA could affect regeneration of the pectoral fin in zebrafish. We report that, depending on the concentration and the experimental schedule, RA can have both teratogenic (narrowing of the fin and fusion of rays) and morphogenetic (increased number of ray segments) effects on the regenerating fin, but, unlike in the amphibian limb, these effects often overlap. Furthermore, while the teratogenic effect seems to affect mainly the dorsoventral axis, the morphogenetic effect is observed on the proximodistal axis. Our work suggests that the zebrafish fin may provide another valuable model to study regeneration and pattern formation of animal appendage. (C) 1994 Wiley-Liss, Inc.