Aggregation in vivo of dissociated cells. II. Role of developmental age in tissue reconstruction.

Abstract

AbstractDissociated skin cells from 5‐ to 14‐day old chick embryos were placed on the chorioallantoic membrane of host embryos as a suspension or after preaggregation in vitro and were allowed to develop as grafts for 6–10 days. The capacity of cells from younger and older embryos to reconstruct feathers was examined and found to differ characteristically. Young cells, from 5‐ to 8‐day embryos (pre‐placodal and placodal feather stages), reconstructed normal feathers in advanced states of differentiation within large thin‐walled vesicles lined by unkeratinized epithelium. Cells of intermediate age, 10‐day old embryos (hump stage feathers), reconstructed feathers which showed typical histological differentiation into barb ridges and pulp, but were atypical in overall plan; skin epithelium was formed usually as compact keratinizing cysts, sometimes as thin unkeratinized linings of expanded vesicles. Cells from older skin, from 12‐ to 14‐day old embryos, did not reconstruct feathers, but, instead, formed extensive sheets of thick, stratified, keratinized epithelium associated with a dense dermal stroma.These results indicate that cells dissociated from the dermal papilla at post‐placodal stages do not initiate de novo feather morphogenesis. This loss of capacity for feather reconstruction which accompanies advancing developmental age is discussed in terms of known epithelial‐mesenchymal interactions and is considered as a consequence of several possible events: (a) loss of inductiveness by the dermis, (b) loss of responsiveness by the epidermis, (c) loss of cell recognition in sorting out processes, (d) active suppression of sorting out or inductive interactions by conflicting concomitant developmental processes.