Transfilter studies on neural induction in the newt.

In order to study the transmission mechanism of neuralising signals during primary embryonic induction, the interacting components (competent newt gastrula ectoderm and dorsal lip tissues) were separated by filter membranes of varying pore size. Nuclepore filters with nominal pore size from 0.1 to 8 mum were employed and the neuralising effect was shown to traverse all of these membranes. Electron microscopic examination did not reveal any cytoplasmic processes in the pores and the authors conclude that the morphogenetic signals are carried by transmissable compounds rather than through direct cytoplasmic contacts.