Transfilter lens induction in avian embryo.

The directive influence of the optic vesicle during lens induction of 2-day chick embryos was studied in vitro. Trunk ectoderm was chosen for the responding tissue. This uncommitted ectoderm formed distinct lentoid bodies when grown together with the optic vesicle. Crystallin synthesis was demonstrated in the lentoids with fluorescein labelled antiserum. By interposing filters of different thicknesses and pore sizes between the interacting tissues, three questions were put forward: (1) Whether the intimate contact between the interactants was essential for induction, (2) how far the inductive influence of the optic vesicle extended, and (3) what was the smallest pore through which the inductive influence could penetrate. The inductive influence reached across a Millipore filter with a thickness of 100 micrometer. It also penetrated a dialyzer membrane, allowing passage of molecules with molecular weights (MW) of less than 12,000 daltons. It was concluded that the directive, inductive signal(s) passing from the optic vesicle, diffused in the extracellular space as far as 100 micrometer and had a molecular weight of less than 12,000 daltons.