Expression of β keratin genes during skin development in normal and [formula omitted] chick embryos

Abstract

The expression of RNA sequences specific for scale beta (β)-keratins has been followed during skin development in normal and scaleless ( sc sc ) embryos. Total RNA from skin at various stages (36–46) of development, as well as newly hatched chicks, was immobilized on nitrocellulose paper and hybridized with a [ 32P]cDNA probe to β-keratins (pCSK-12). Sequences for β-keratins showed patterns of expression which were specific for each genotype and scale type examined. During the development of normal scutate scales, which are characterized by the formation of a beta stratum, RNA with β-keratin sequences first appeared at stage 40, and continued to accumulate through hatching. RNA with β keratin sequences appeared in scaleless skin between stages 40 and 41, was greatly diminished by stage 44, and was no longer present at stage 46. In normal reticulate scales, which like scaleless skin, do not develop a beta stratum accumulation of RNA with β-keratin sequences was limited to a brief embryonic period between stages 42 and 44. These patterns of RNA expression correlated well with the appearance of β-keratin polypeptides, suggesting that β-keratin synthesis may be controlled at the level of keratin mRNA transcription. Correlations between the patterns of β-keratin expression and histological events suggest that the brief accumulation of β-keratin mRNA in scaleless skin and normal reticulate scales is related to the formation of the subperiderm (a protective layer of cells, peculiar to embryonic skin) while the continuous accumulation of β-keratin mRNA during scutate scale development reflects the formation of a beta stratum.