Regulation of chick CYP26 developmental signaling pathways
Description
It has been known for over three quarters of a century that Vitamin A and its derivatives (retinoids) are essential for both normal embryonic development and in the maintenance of adult tissues (Collins and Mao, 2000). Classical data demonstrated that high levels of all-trans-retinoic acid (RA) or a deficiency of vitamin A in vertebrates can lead to a number of birth defects (Ross et al., 2000). These observations suggest that a precise control of the levels of RA in cells and tissues is required for proper development and function. In vertebrates, one mechanism by which the levels of RA can he regulated involves the action of CYP26 enzymes, which are members of the cytochrome P450 superfamily of catabolizing enzymes. Members of the CYP26 family have been isolated from different systems, including the chick embryo. In the chick, RA found to induce the expression of the CYP26 (cCYP26) gene in the limb bud in vivo (Swindell et al., 1999). However, whether the induction of cCYP26 by RA was a dose- or stage-dependent process in vivo was not addressed in that study. In addition, whether all the regions of the limb bud respond equally to RA by inducing the expression of cCYP26 or whether other signaling pathways are involved in this inductive mechanism is still not known. In the present work, implantation of RA-soaked beads at different stages and position in the chicken wing bud demonstrated that cCYP26 is induced by RA in a stage-, dose-, and position-specific manner, and that cells in the posterior limb mesenchyme are more resistant to the induction of cCYP26 by RA. Subsequent experiments demonstrated that the ZPA, acting through Shh, contributes to the differential induction of cCYP26 expression by RA in the anterior versus posterior limb mesenchyme. Thus, these results suggest a mechanism by which Shh signaling can regulate the induction of expression of certain RA-responsive genes in the developing chicken limb bud. Finally, effort was done in order to characterize a suitable in vitro model for the study of the regulatory mechanism exerted by Shh on the RA-induced cCYP26 expression