Identification, expression, and localization of β keratin gene products during development of avian scutate scales

Abstract

Abstract Epidermal-dermal interactions influence morphogenesis and expression of the β keratin gene family during development of scales in the embryonic chick. The underlying mechanisms by which these interactions control β keratin expression are not understood. However, the present study of β keratin gene expression during avian epidermal differentiation contributes new information with which to investigate the role of tissue interactions in this process. Using β keratin-specific synthetic oligonucleotide probe, β keratin mRNA was hybrid-selected from total poly A + RNA of scutate scales. Seven β keratin polypeptides were translated in vitro and could be identified by their positions in two-dimensional gels among the detergent-insoluble extracts of scutate scale epidermis. In vivo phosphorylation studies suggested that an additional three β keratin polypeptides were present as phosphoproteins. The temporal appearance of β keratin mRNA and the corresponding polypeptides was followed during scutate scale development. Polyclonal antiserum made against two of the β keratin polypeptides was used for immunohistochemical and immunogold electron-microscopic analysis of β keratin tissue distribution. Immunological reactivity was observed specifically along the outer scale surface in epidermal cells above the stratum germinativum. Immunogold beads were localized on 3-nm filament bundles. In situ hybridization with a β keratin-specific RNA probe demonstrated that mRNA accumulated in the same regional manner as the polypeptides. This selective expression of β keratin genes in specific regions of the developing scutate scale suggests that epidermal-dermal interactions provide not only for morphological events, but also for control of complex patterns of histogenesis and biochemical differentiation.