
<ArticleTitle>Differential expression of chicken <prot>CYP26</prot> in anterior versus posterior limb bud in response to retinoic acid.</ArticleTitle>
<AbstractText>Multiple studies indicate that quantitative control of the levels of all-trans-retinoic acid (RA) in the vertebrate embryo is necessary for correct development. The function of RA in cells is regulated by a number of coordinated mechanisms. One of those mechanisms involves controls on the rate of RA catabolism. Recently, enzymes capable of catabolizing RA were found to constitute a new family, called <prot>CYP26</prot>, within the <prot>cytochrome P450</prot> superfamily. <prot>CYP26</prot> homologues have been isolated from human, mouse, zebra fish, and recently from the chick. In this study, we examined the regulation of chicken <prot>CYP26</prot> (<prot>cCYP26</prot>) expression by RA during the early phase of chick limb outgrowth. In the anterior limb mesenchyme and apical ectodermal ridge (AER), <prot>cCYP26</prot> expression was induced in a concentration dependent manner by implanting beads soaked in 0.1, 1, and 5 mg/ml RA. The RA-induced expression of <prot>cCYP26</prot> in anterior limb mesenchyme and the AER was detected as early as 1 hr after treatment and was not affected by the presence of cycloheximide. In contrast to the anterior limb, the induction of <prot>cCYP26</prot> was dramatically reduced (or absent) when RA beads were implanted in the posterior limb mesenchyme. Furthermore, induction of <prot>cCYP26</prot> expression in the anterior mesenchyme was inhibited by transplantations of the zone of polarizing activity (ZPA) and by Shh-soaked beads. Our data suggest that different mechanisms regulate retinoid homeostasis in the AER and mesenchyme during limb bud outgrowth. J. Exp. Zool. 290:136-147, 2001.</AbstractText>
