FIG 4.

Dasy-Env1.1 is a fusogenic retroviral envelope protein. (A) Assay for cell infection mediated by Dasy-Env1.1-pseudotyped virus particles. Pseudotypes were produced by cotransfection of human 293T cells with expression vectors for MLV core, the Dasy-Env1.1 protein (or an empty vector), and a lacZ-containing retroviral RNA. Supernatants were used to infect a panel of target cells, which were stained with X-Gal 3 days after infection. Infected LacZ⁺ cells were detected in a series of cell lines (see Results), including human HeLa and SH-SY5Y cells, but not in A23 cells. (B) Assay for cell-cell fusion mediated by Dasy-Env1.1. A panel of cell lines was transfected with an expression vector for Dasy-Env1.1 or an empty vector (none) together with a LacZ expression vector. Cells were cultured for 48 h after transfection, fixed, and stained with X-Gal. LacZ⁺ syncytia (red arrows) were detected in human HeLa and SH-SY5Y cells but not in A23 cells, with only mononucleated cells being visible by using the empty vector. Original magnification, ×100.