Aggregation in vivo of dissociated cells. III. Effect of state of differentiation of cells on feather development in hybrid aggregates of embryonic mouse and chick skin cells

The relation of embryonic age and state of differentiation of cells to their capacity to reconstruct integumental tissues was studied in aggregates of cells dissociated from the skin of 13‐ to 15‐day mouse and 8‐day chick embryos. To attain advanced morphogenesis of the reaggregates, cell suspensions were placed and aggregated on the chorioallantois of chick embryos; the following cell combinations were studied: (1) chick skin cells (epidermal and dermal; (CS), (2) mouse skin cells (epidermal and dermal; MS), (3) MS commingled with CS, (4) mouse epidermal cells (M e ) commingled with CS, (5) mouse dermal cells (M d ) commingled with CS. Reaggregated MS from 13‐ to 15‐day embryos reconstructed typical mouse skin structures: hair and stratified, keratinized epidermis. Similarly, reaggregated CS reconstructed typical feathers and thin nonkeratinized skin. In bispecific CS + MS aggregates, MS from older embryos (14–15 days) completely suppressed feather development, but formed hair and sheets of bispecific chimeric keratinized epidermis. In contrast, MS from 13‐day embryos co‐aggregated with CS did not suppress feather morphogenesis; in such bispecific aggregates both hair and feathers developed, as well as chimeric epidermis. Most striking was the frequent formation in this combination of “chimeric feathers” in which mouse cells were included in feather structures. M e contributed to the epidermal elements of the feather; M d formed groups at the site of the feather dermal papillae. This changeover in mouse cells from participation in feather morphogenesis in aggregates to its suppression is closely correlated with their developmental age. The contributions of these results to the understanding of histotypic specificity and morphogenetic cell interactions are discussed.