Morphogenesis of the feet of birds, studied in limbs developed from reaggregated heterospecific mesoderm
Experiments were undertaken to determine whether species-specific characters of chick and duck mesodermal leg-bud cells are retained after dissociation and reaggregation in homoand heterospecific mixtures.
Prospective zeugopod and autopod mesoderm from chick and/or duck leg buds were isolated, dissociated into a cell suspension and pelleted by centrifugation. The reaggregated mesoderm was packed into a leg-bud ectodermal jacket; the recombined leg bud was then grafted on the wing stump of a host embryo. Recombinants whose mesoderm was a homospecific reaggregate developed into typical chick or duck leg parts according to the specific origin of the mesodermal component; the feet of nearly all these legs lacked antero-posterior polarity. Recombinants containing heterospecific reaggregates were also capable of forming reasonably organized leg structures.
The foot was not, as a rule, of the specific type expected of the majority component. In a mixture of 75% chick mesoderm cells and 25% duck mesoderm cells, the feet which developed were either of chick type or of composite chick/duck type, where typical chick areas were next to typical or aberrant (steganoid) duck areas. When the ratio was reversed (25% chick, 75% duck), the majority of the feet were again of chick type or of composite chick/duck type, the typical duck phenotype being exceptional. Even in a mixture of 10% chick cells and 90% duck cells, duck-type feet were not obtained. They were all of composite type: half of their interdigital zones were of chick type, the other half were occupied, in most cases, by underdeveloped, indented webbing or by one or several discrete flaps, and, in a few cases, by normal webbing.
The vast majority of the feet developed from heterospecific mesoderm were characterized by the profusion of the toes, which were not polarized along the a–p axis.
The use of a slide spinner in the analysis of cell dispersion.
