FIG. 1.

HERV-W glycoprotein envelope can use both hASCT2 and hASCT1 to induce cell-cell fusion. CHO cells expressing either hASCT1 or hASCT2 and human cell line TE671 were transfected with RD-Rless, BaEV-Rless, HERV-W, or LacZ (control) expression vectors. The determination of the fusion activity of the transfected envelope glycoproteins was performed at 24 h posttransfection. (A) The cultures were fixed and stained with May-Grunwald and Giemsa solutions. Magnification, ×100. (B) Histogram showing the mean fusion index of each combination of cell-cell fusion assay (error bars are standard deviations; n = 4). The fusion index represents the percentage of fusion events in a cell population and is defined as [(N − S)/T] × 100, where N is the number of nuclei in syncytia, S is the number of syncytia, and T is the total number of nuclei counted (2).