Chapter 11 Dual Regulation of Expression of Exogenous δ–Crystallin Gene in Mammalian Cells: a Search For Molecular Background of Instability in Differentiation

Abstract

Crystallins are a group of soluble proteins specific to the vertebrate lens. Among the crystallins, δ-crystallin is found only in avians and reptilians; in the chicken it is the earliest one to be expressed during lens development. It represents the most abundant crystallin in the lens. Crystallins can be used as the molecular markers of lens differentiation. It has been repeatedly demonstrated that certain ocular tissues other than lens, such as neural retina and retinal pigmented epithelium, also transdifferentiate to form lens cells in appropriate culture conditions. One of the criteria, other than morphology, used to demonstrate this overt cell change is the expression of all the crystallin classes. In addition to crystallin expression associated with lens differentiation, this chapter focuses on the expression of δ-crystallin in certain ectopic tissues as well, either in embryos or in tissue cultures in vitro. Ectopic δ-crystallin expression is characterized not only by its very low level, but also by the absence of any other crystallins. Ectopic δ-crystallin expression is discussed in the chapter in terms of the idea of it representing a rudimental lens differentiation. It is important to investigate the molecular mechanism to know why the gene coding for δ-crystallin is “leaky”. Such studies may not only uncover the mechanism of transdifferentiation into the lens of nonlenticular tissues both in regeneration and in cell cultures, but may also contribute towards understanding the molecular background of the unstable nature of cell differentiation in general.