Control of tissue specificity: the pattern of cellular synthetic activities in tissue transformation.

Abstract

During transformation of the dorsal marginal iris into lens tissue after removal of the lens in the adult newt, the cells undergo gradual changes in synthetic activities. Autoradiographic data indicate an enhancement of RNA synthesis in the nucleus of iris cells, which is followed by enhancement of protein synthesis and onset ot DNA synthesis. After discharge of pigment granules and a period of cellular multiplication accompanied by ribosome production, the cells stop DNA synthesis and start to show detectable amounts of lens-specific proteins (α-,β-, and γ-crystallins). This time coincides with initiation of differentiation of primary lens fibers. In the later stages of regeneration, α- and β-crystallins are present in the dividing cells of the lens epithelium, as well as in the cells of the fiber area, but γ-crystallins are detected only in Che cells of the fiber area. The data were interpreted as suggesting that the gene utilization pattern typical for the iris is not directly converted into that for the lens, but goes through intermediate patterns before the tissue transformation is completed.