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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.