Transmission and spread of embryonic induction

Abstract

ABSTRACT The question of whether inductive tissue interactions involve factors transmitted by long-range diffusion was investigated. In transfilter experiments with spinal cord as the inductor and metanephric mesenchyme as the responding tissue it was established that interposition of a second TA Millipore filter (pore size 0·8 μm, thickness 25 μm) prolongs the induction time by about 12 h. The prolongation of the induction time was concluded to be due to the time taken by the inductor to pass through the second filter. It was also demonstrated that metanephric mesenchyme partially lost its competence if precultivation lasted more than 12 h. This explains why 100% induction never was achieved in the double-filter experiments. In order to rule out the possibility that the filters, owing to their inhomogeneous structure and negative surface charge, seriously restricted diffusion, the diffusion of several substances through the filter was measured under conditions as closely similar as possible to those in the transfilter experiments. Although there was some restriction of diffusion, the calculated diffusion constants were of the same order of magnitude as those reported in the literature, indicating that the filter is no major obstacle. Calculations based on four different hypotheses that the inductor is transmitted by diffusion, indicate that diffusion can hardly explain the long transmission time.