MENON, J.; ROBERTS, R.*; DAVILA, I.: Influence of peroxisome proliferator activated receptor (PPAR) and retinoid receptor agonists on tail epidermis and limb buds of Xenopus laevis in vitro.

Members of the superfamily of nuclear hormone receptors, which are obligate heterodimeric partners of the retinoid X receptors, may be important in amphibian post-embryonic development. Here, we examined the effects of retinol palmitate, and of clofibrate (agonist of peroxisome proliferator activated receptors � PPARs) on two organs – tail epidermis and limb bud of the tadpoles of Xenopus laevis in vitro . Amputated tails and limb buds during (stage 54/55, Nieuwkoop and Faber, 1967) were maintained in vitro with two retinol concentrations (10^-6 M,10 ^-5 M) and clofibrate (10 ^-3 M). Tails and limbs were maintained in culture medium for 72 h and 96 h respectively and tissues were processed for electron microscopy. In Xenopus laevis , tail epidermis is bi-layered with underlying collagen layers. While there were no observable changes in tail epidermis retinol concentration of 10^-6 M, higher retinol concentration (10 ^-5 M) induced large-scale apoptosis and sloughing of the epidermis. Limb buds, when treated with retinol showed differentiation of the digits. Clofibrate treatment induced significant epidermal lipid deposits and loss of structural integrity of tail epidermis. No change in cartilage differentiation was observed in the limb buds following clofibrate treatment. We hypothesize that at developmental stage 54/55, PPAR agonists may not have a significant role to play in limb morphogensis in contrast to ligands of retinoid receptors and the effects of PPAR agonist in tail tissue may be related to a different developmental fate (regression) of this organ.