Investigation of the basic process of cell differentiation utilizing mutant animals of crystallin regulators

点击翻译按钮获取中文摘要

We have aimed at elucidation of the process of lens differentiation as a paradigm of cell differentiation with special attention to transcriptional regulation. It is remarkable that lens cell undergo terminal differentiation exceptionally early in embryogenesis. Onset of lens differentiation is marked by initiation of crystallin gene expression in addition to morphological change of the tissue. We focused on regulation of delta-crystallin gene of the chicken because delta-crystallin is the earliest and the most abundantly synthesized crystallin in avian lenses.Mutational analysis of the delta-crystallin enhancer core identifed two positive regulatory elements which are interdependent. From this and EMSA of lens nuclear extract, it was concluded these two elements correspond to binding sites of two distinct activators, deltaEF2 (Sox-1 to 3) and deltaEF3. A repressor deltaEF1 modulates the activity of deltaEF3. It was also shown that Sox binding is required for the promoter activity of the mouse gamma-crystallin gene, providing evidence that diversified crystallin genes are regulated, at least partly, by a common mechanism.The Sox proteins 1 to 3 are shown to be essential for crystallin regulation, and from chronology and spatial distribution of their expression they are good candidates as a key factor of lens differentiation. Pax-6 also seems involved in these processes, but its contribution seems to be in larger number of steps than only provoking lens diffentiation. It looks as if Pax-6 is involved in endowment of eyeness to the tissues in global terms, while Sox-1 to 3 are in determination of lensness in the ectoderm. These two factors appear essential for eliciting lens differentiation, but by themselves they are not sufficient, and more intrinsic and extrinsic factors are probably necessary for lens differentiation to occur. deltaEF3, currently under investigation, may be one of these essential factors.