Retroviral expression of connexins in embryonic chick lens.

PURPOSE To develop an in vivo model system in which exogenous proteins can be expressed in embryonic chick lens and to further understand the function of connexin-mediated gap junction intercellular communication in lens cell biology. METHODS RCAS(A) is a replication-competent chicken retrovirus that infects dividing cells. Retroviral constructs were prepared containing alkaline phosphatase (AP) and FLAG-tagged connexins. Chick lenses were infected in situ by injecting virus into the lumen of lens vesicles at stage 18, cultures were taken at various periods. The lenses were then dissected, and the expressed proteins were visualized by AP histochemical examination and immunostaining. RESULTS Twenty-four hours after infection, alkaline phosphatase could be seen in epithelia and fibers. As lens fiber maturation progressed, however, the alkaline phosphatase staining was lost as the fibers matured, presumably because of the proteolytic removal of the enzyme. By 72 hours, alkaline phosphatase staining could still be observed in epithelial cells and in differentiating fibers in the bow region but not in the mature lens fibers. FLAG-tagged exogenous lens connexins were also abundantly expressed by viral infection. The exogenous connexins were localized at the cell surfaces in junctional maculae and showed the same cell-type specific distribution as that of their endogenous connexin counterparts. CONCLUSIONS An in vivo model system has been developed in the chick that provides opportunities to study the expression of wild-type and mutant proteins during lens differentiation. Expression of wild-type connexins has revealed that the characteristic distribution of the three different lens connexins is maintained even when expression is driven by a viral promoter.