Lens-specific activity of the chicken delta 1-crystallin enhancer in the mouse

A lens-specific enhancer was identified in the third intron of the chicken delta 1-crystallin gene by analysis based on transient transfection of primary-cultured cells. To assess the significance of this enhancer's activity in embryonic lens cells during development, tkCAT gene carrying the enhancer was introduced into mouse embryos utilizing ES (embryonic stem) cell-mediated gene transfer. In the undifferentiated culture condition, ES lines with enhancer-carrying tkCAT did not express any significant level of CAT (chloramphenicol acetyltransferase). However, when the ES cells were injected into a blastocyst and allowed to differentiate into various somatic cells of an embryo, CAT expression was observed exclusively in lens, and the expression was dependent upon the delta 1-crystallin enhancer. We concluded that the delta 1-crystallin enhancer alone is sufficient for eliciting lens-specific gene expression in developing mouse embryos and that the mechanism of lens-specific regulation effected by the delta 1-crystallin enhancer is conserved between the chicken and the mouse.