Direct effects of retinoic acid on the development of the tail bud in chick embryos

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Abstract
Retinoic acid (RA) has been reported to induce vascular lesions and haematoma formation in the vicinity of the tail bud during the critical period for inducing abnormalities of tail bud development in hamsters (Wiley, '83; Tibbles and Wiley, '88), mice (Tibbles and Wiley, '88) and chicken embryos (Jelinek and Kistler, '81). Experiments were conducted to determine whether or not these vascular lesions were the primary cause of the malformations which they accompanied. Chick embryos were exposed for varying lengths of time to several dosages of RA. Primitive streaks or tail buds from treated embryos were then excised prior to vascularization and transplanted to the coelomic walls of untreated host embryos. The grafts were harvested at 3 or 6 days after grafting and processed for histological examination. Observations of serial sections of controls showed that the primitive streak and early (stage 13–14) tail bud were able to form neural tubes and a variety of other structures including ganglia, nerve fibres, and kidney tubules. Treatment of donor embryos with RA prior to grafting, however, affected the frequency and characteristics of the neural tubes and other tissues developing in the grafts. The effects of RA on development were correlated with both the dosage and length of exposure to the teratogen prior to grafting. Since the grafts were made before the appearance of blood vessels in the tail buds, we have concluded that the effects of RA on the development of tail bud tissues, and especially the secondary neural tube, are direct and are not mediated solely through the disruptive effects of vascular lesions seen in intact embryos.