Tissue-specific expression of a cloned chick delta-crystallin gene in mouse cells

Crystallins are a group of soluble proteins specific to vertebrate lenses, and have been used successfully as molecular markers for studying lens differentiation. The synthesis and accumulation of delta-crystallin in the differentiating lens cells of chick, in particular, have been extensively studied (for review see refs 1-3). Recently, we have cloned a continuous stretch of a chick delta-crystallin gene which is specifically expressed in lens cells. We have injected this gene into nuclei of various mouse somatic cells. delta-Crystallin is totally absent from mammalian lenses in which it is replaced by gamma-crystallin, thus this xenogeneic injection system should allow us to study tissue-specific gene expression. We report here experiments which demonstrate that (1) the cloned delta-crystallin gene of chick is expressed in the mouse lens epithelial cells as efficiently as in the homologous chick cells; (2) delta-crystallin synthesized in the mouse lens epithelium has the native molecular weight, indicating correct splicing of the gene transcripts; (3) the expression is inefficient in the non-lens tissues examined, suggesting lens-specific expression of the delta-crystallin gene in the xenogenic environment. To our knowledge, this is the first demonstration that a cloned gene shows preferential expression in homologous cell types of different species.