Differences in the histogenesis and keratin expression of avian extraembryonic ectoderm and endoderm recombined with dermis

Abstract

The responses of the chorionic ectoderm and allantoic endoderm (from 8-day chick embryos) to dermal induction were compared through tissue recombinants grafted onto the chorioallantoic membrane. The chorionic epithelium formed the appropriate epidermis with a fully developed stratum corneum in response to both spur and scutate scale dermises. Analysis of these recombinant epidermal tissues by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) demonstrated that tissue-specific expression of the alpha (α) and beta (β) keratin polypeptides occurred. In addition, indirect immunofluorescence studies with antisera to α or β keratins showed that the beta stratum, which characterizes the epidermis of spurs and scutate scales, was formed, and the α keratins were distributed as in the normal epidermal tissues. In contrast, although the allantoic endoderm became stratified in association with either spur or scutate scale dermis, a stratum corneum with a beta stratum did not develop. SDS-PAGE analysis demonstrated that while the characteristic β keratins of scutate scales and spur were not detected, most of the α keratins normally elaborated by these structures were present, suggesting that even without histogenesis of a stratum corneum the expression of α keratins of endoderm could be regulated in a tissue-specific manner by dermis. This study also demonstrated that there are differences in the abilities of the chorionic and allantoic epithelia to respond to the same dermal cues, which may reflect earlier restrictions in their developmental potentials.