Conditions permitting the homotopic expression of lens-specific crystallin genes

δ-Crystallin is a major soluble protein of the avian and reptilian lens, and its expression is highly tissue-specific in development. In order to understand regulatory mechanisms for tissue-specific expression of δ-crystallin gene, several experimental systems were established in a heterologous combination of the chicken gene and mouse cells. The expression was ectopic in various cell types differentiated in teratomas derived from mouse teratocarcinoma or embryonic stem cells which were transformed to carry the chicken δ-crystallin genes. Cells of the same transformed lines of embryonic stem cells expressed the chicken gene homotopically in chimeric embryos produced by injecting them into the blastocysts. The homotopic expression also occurred in experimental systems consisting of the heterologous introduction of the gene (1) into various mouse cells in primary cultures, and (2) into male pronuclei of mouse fertilized eggs.