The pattern of expression of chick delta-crystallin genes in lens differentiation and in trans-differentiating cultured tissues.

During development of the vertebrate lens, the lens epithelium undergoes a final stage of differentiation into lens fibre cells. Lens fibre cells can also be produced by trans-differentiation from certain extralenticular structures, all of which are of different developmental origin from lens, including embryonic neural retina and retinal pigmented epithelium. Delta-crystallin is the major lens protein in the chick and appears first in development; it is the major product in trans-differentiated retina of younger embryos. In both normal differentiation and trans-differentiation an increase of delta-crystallin coding RNA is detectable in the nucleus of cells prior to their terminal differentiation into lens fibres. The increase in transcription of delta-crystallin genes accompanying final differentiation of lens fibres, appears to take place slightly in advance of an increase in the capacity to process and transport this mRNA to the cytoplasm.