Development of interdigital tissue as revealed by conditions that alter its fate

The effect of Janus green B (JGB) on avian limb cell migration was studied by excising small portions of interdigital tissue from between all digits and culturing these explants with 10 μg/ml JGB. All interdigital cell migration was inhibited by this dose. In a similar experiment wedges of interdigital tissue from between digits III and IV were incubated in 1.0-10.0 μg/ml JGB. The results gave a typical dose response curve in which almost complete inhibition occurred with the high doses of JGB and lower doses gave less inhibition. A second series of experiments was undertaken to study interdigital cell migration in vivo. However, it was discovered that transplantation of interdigital tissue resulted in ectopic chondrogenesis. This change of fate of these cells from death, and possibly migration, to chondrogenesis thus became part of the focus of this study. In addition to transplantation, simple incisions were cut into III-IV interdigital tissue. Wounding interdigital tissue resulted in ectopic chondrogenesis. The more severe the wounding the more digit-like the extra cartilage. Transplantation of a complete interdigital zone resulted in the development of a complete extra digit and simple incisions resulted in the development of a partial digit. To determine if exposure of the injured surfaces to amniotic fluid (AF) caused the ectopic chondrogenesis, amniotic fluid was removed and replaced with sterile phosphate buffered saline (PBS) prior to doubly incising interdigital tissue. This failed to inhibit the ectopic chondrogenesis. Exposing interdigital tissue to AF in vitro also failed to inhibit chondrogenesis. These results suggest changes within the interdigit, possibly to nutrient or oxygen availability, are responsible for the formation of ectopic digits.