An investigation into two photostable retinoids and their use as tools to study retinoid function in vivo.

Abstract

All-trans retinoic acid (ATRA) is essential for embryonic development and adult homeostasis. Its study has been hindered by the fact that it can be converted to isomers upon exposure to light and because its metabolites are also bioactive molecules. Recent research has indicated that ATRA can also activate two different receptor pathways in vitro and in vivo.

The present study investigates the effects of these isomers and metabolites on chick wing development using two synthetic, photostable retinoids, EC23 and EC19. These retinoids have identical structures bar the position of the terminal carboxylic acid group but surprisingly, generate different effects in vitro and in vivo, and are differentially metabolised by metabolising enzymes. EC23 mimics most of the effects of ATRA in vivo, including the novel phenotype of scapula malformation, while EC19 does not. Their phenotypes are further characterised in the text but EC23 produces a novel retinoid phenotype characterised by duplications of solely forelimb digit 1.

The mechanisms behind the phenotypes generated by EC23 and EC19 are explored with respect to retinoid metabolism and localisation of ATRA binding proteins at the stage of application. Both ATRA signalling pathways are investigated at HH20 of chick embryonic development which improves our understanding of the role of retinoids in limb and embryonic development. Comparison of gene expression in response to ATRA and EC23 indicates that the metabolites and isomers of ATRA do not play a role in embryonic limb development, as well as highlighting avenues for further research into the development of the scapula and elbow. A major part of the retinoid response is to stall limb development while retinoid levels recover. By comparison with other teratogens, this may be part of a common response and be pertinent to the regulation of normal embryonic development by retinoids.