Recent progress in studies of the transdifferentiation of eye tissue in vitro.

A major switch in the overt differentiation phenotypes, which we call transdifferentiation, occurs very often in cultures of embryonic eye tissues. The systems provide irrevocable evidence for instability in the results of cell differentiation, and hence, studies on this topic are expected to contribute much to the understanding of the basic mechanisms of cell differentiation. In this article, recent work on transdifferentiation, mostly with chick embryos, was reviewed. Several new systems of lens transdifferentiation starting from brains, adenohypophyses, and other tissues have recently been discovered. Regarding the widely known cases of transdifferentiation starting from neural and pigmented retina cells, there has been considerable progress in elucidating the factors controlling such major switches in differentiation. In particular, efforts are under way to attempt to understand the mechanisms of transdifferentiation in relation to the transcriptional control of genes coding lens-specific proteins.