Gal-1 is necessary for optimal fusion of trophoblastic cells. A) Primary vCTBs were cultivated for 4 d in absence (left panels) or presence (right panels) of lactose. Plasma membrane (green) and nuclei (red). B) BeWo cells were treated with DMSO or forskolin (FSK; 50 µM) for 24 h before addition of PBS or lactose. Plasma membrane (green), nuclei (blue). Cellular fusion index, expressed as percentage of fusion, was calculated for each condition using the following formula: (NS/NT) × 100, in which NS is the number of nuclei in syncytia and NT is the total number of nuclei. *P < 0.05 (2-way ANOVA). C) BeWo cells were transfected with scrambled or Gal-1 siRNA and were then treated with either DMSO or FSK (50 µM). Cells were fixed and plasma membrane (green) and nuclei (red) stained 24 h after treatment to visualize cell fusion events. Lac, lactose; ns, not significant. Scale bar, 10 µm.