CAUDAL FIN REGENERATION IN WILD-TYPE AND LONG-FIN MUTANT ZEBRAFISH ISAFFECTED BY RETINOIC ACID

Zebrafish (Danio rerio) represents an ideal experimental model to tack le fundamental issues concerned with organogenesis during development and regeneration of complex body structures. We discuss here the devel opment of the skeleton in zebrafish caudal fins, their regenerative ab ility in wild type and long-fin mutant adult fish, and how retinoic ac id IRA), which induces duplications along the proximodistal axis in re generating limbs, affects regeneration of the caudal fin. The dorsal a nd ventral lobes of zebrafish caudal fins are apparently symmetrical a long the dorsoventral axis, but all of the skeletal elements and most of the soft tissues of both lobes originate from the ventral part of t he embryo, as demonstrated by whole-mount staining of developing fish. Analysis of caudal fin regenerates in wild type adults does not revea l any difference in the regenerative ability of the two lobes, and in the length of the regenerate in comparison with the amputated part. In contrast, in the long-fin mutant the regenerated caudal fin is always somehow defective in that the original asymmetry in the length of the two lobes observed in this mutant is not reproduced in the regenerate . Furthermore, in the majority of the batches studied the regenerate i s much smaller in size than the amputated part. This suggests that thi s mutant may be valuable to further our understanding of the mechanism s underlying growth control and patterning during regeneration. Finall y, we show that the regenerating caudal fin is sensitive to RA-treatme nt, and clear teratogenic effects on the dorso-ventral axis are observ ed under many of the experimental conditions investigated both in wild type and long-fin mutants. However, RA can neither induce formation o f extra-long fins in the wild type, nor restore mutant fins to their o riginal length.