الفهرس | Only 14 pages are availabe for public view |
Abstract Owing to the importance and effective role of vitamin A and its derivatives such as retinoic acid (RA) which is considered as a key for several biological processes during development, therefore, the objective of this study was an attempt to have a deep insight on the critical role of RA during morphogenesis of chick embryo using different concentrations of RA. Fertilized eggs of the chick Gallus domesticus were divided into five groups. These groups were, control and four injected groups. The 1st group was injected with 1μl of the solvent (DMSO), the other three groups received 0.5 μg, 1 μg and 2 μg of RA, each was dissolved in 1 μl of DMSO. The injection was achieved after three days of incubation. Morphological studies were carried out at 1, 3, 5, 7, 10 and 15 days after treatment, while the histological examinations were carried out at 1, 3 and 5 days after treatments using H&E stain. The data were statistically analyzed using SPSS and Excel software. Results indicated that RA treatment induced teratogenic effects during morphogenesis of the developing chick embryos. The defects included malformations in the brain, head, eye, nostril, beak, neck, trunk region, fore and hind limbs and tail region. Results revealed the disappearance of some proximal parts of the limbs of some embryos. This was explained as a downregulation effect of RA on the genes responsible for the maintenance of such proximal parts and consequently their disappearance. Histological examination indicated some degenerative activity and changes in the pattern of morphogenesis in the nervous tissues. Explanation of the effect of RA based on the induction of cell death and the disturbance of normal pattern of expression of genes concerned with the process of morphogenesis. Results indicated that low concentration of RA (0.5 μg) induced teratogenic effects more than the higher concentrations (1 μg and 2 μg) and this was explained on the basis of a feedback controlling system achieved by RA degrading enzymes. |