Figure 6.

Trans-uptake of Delta and Notch in Drosophila S2 cell aggregation assays. In panels A-C, antibodies to Delta are detected with fluorescein-conjugated secondary antibodies (green); antibodies to Notch are detected with Texas Red-conjugated secondary antibodies (red). These panels present merged confocal images. Colocalized Delta and Notch appear yellow. (A) Antibodies to the Delta extracellular domain colocalize with antibodies to the Notch intracellular domain in vesicular structures within a Notch⁺ cell (arrow). (B) Antibodies to the Delta intracellular domain colocalize with antibodies to the Notch intracellular domain in vesicular structures within a Notch⁺ cell (arrow). (C) Notch⁺ cells aggregated with cells that express DeltaNGIC, a Delta-neuroglian chimera, in which the Delta intracellular domain is replaced with the neuroglian intracellular domain. Antibodies to the Delta extracellular domain colocalize with antibodies to the Notch intracellular domain within vesicles in Notch⁺ cells (arrows). (D) In Notch⁺ cells aggregated with cells that express DeltaNGIC, antibodies to the neuroglian intracellular domain (green) colocalize with antibodies to the Notch extracellular domain (red) within vesicles in Notch⁺ cells (arrows). (E) In Notch⁺ cells aggregated with cells that express DeltaDde, which lacks the Delta intracellular domain, antibodies to the Delta extracellular domain (green) colocalize with antibodies to the Notch intracellular domain (red), within vesicles in Notch⁺ cells (arrows). (F and G) Delta–Notch aggregates stained with antibodies to the Delta extracellular domain (green) and antibodies to the Delta intracellular domain (red). This merged image shows Notch⁺ cells that contain vesicles (which appear yellow) that costain with the Delta extracellular and intracellular domain-specific antibodies. Some vesicles that are recognized by only the extracellular domain antibody (MAb9B, green vesicles, arrow labeled “ec”) or by only the intracellular domain antibody (C2 guinea pig polyclonal antiserum, red vesicles, arrows labeled “ic”) are also found. (H) In cells that express full-length Delta aggregated with cells that express full-length Notch, antibodies to the Notch intracellular domain (red) colocalize with antibodies to the Delta extracellular domain (green) in Delta⁺ cells (arrows). The asterisk indicates a Delta⁺ vesicle inside a Notch⁺ cell.