title: [RNA metabolism in chick embryo skin].
abstract: Explants from 7, 8, 9, 11, 13-day chick embryonic skin incorporating (3H) Uridine for different periods 1 hr, 3 or 4 hr and a chase with actinomycin) are studied with respect to free (F) or membrane bound (B) cytoplasmic polysomes and to RNA extracted from them. Polysome specific activity decreases at older stages but the amount of polysomes increases due to increased protein synthesis. At each stage B polysomes are less abundant but more radioactive than F polysomes. RNA extracted from each kind is analysed on sucrose gradients: one half of each fraction is precipitated by TCA to estimate total radioactivity, the other is retained on millipore at high salt concentration to estimate radioactivity in messenger-like RNAs due to their poly-A sequences. The pattern of the labelling of the different fractions of RNA changes with the length of incorporation, the stages of explants and the kind of polysomes (F or B); at 11-13 days the incorporation is slow, radioactivity is low and distributed among several peaks of poly-A RNA; at 7-8 days the incorportion is rapid, dispersed throughout the gradient; at 9 days, a midway stage, incorporation is particularly high into 12S and 24S fractions from B RNA. In the 5 studied stages the labelling of this 12S occurs early, remains for a longer time and cannot be chased. These observations suggest stability of the 12S RNA. Since, in 14-day chick embryos, feather keratin m RNA has been shown to sediment at 12S and although our experiments have been done with total skin because this differentiating tissue is the site of extensive interactions between dermis and epidermis, they suggest that this 12S RNA is the actual keratin m RNA and might be synthesised some days before the onset of keratin synthesis. Its template ability will be investigated at earlier stages.
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D002458:Cell Fractionation; D002499:Centrifugation, Density Gradient; D002642:Chick Embryo; D003609:Dactinomycin / Q000494:pharmacology; D007633:Keratins / Q000096:biosynthesis; D011132:Polyribosomes / Q000187:drug effects / Q000378:metabolism; D012313:RNA / Q000378:metabolism*; D012867:Skin / Q000378:metabolism*; D013997:Time Factors; D014158:Transcription, Genetic
chemical_list: D003609:Dactinomycin; D012313:RNA; D007633:Keratins
vernacular_title: Métabolisme des RNA de la peau embryonnaire de poulet