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Fig. 2. Fas2 polarization and signaling. (A-A'') Wild-type BC cluster. Fas2, Dlg and Lgl are polarized to the leading half of the PCs (arrowheads; leading-to-trailing Fas2 polarity ratio: 8.6±1.6; see also Fig. 6A-A''). Fas2 is localized at the highest level in the interface between the PCs (A, arrow). (B-B'') Targeting Fas2 to BCs using Slbo-Gal4 (Slbo-Gal4 is not expressed in PCs; D) causes Fas2 to become localized around the circumference of the PCs (leading-to-trailing Fas2 polarity ratio: 1.1±0.2), and dramatically reduced at the interface between the PCs (arrow, compare with A). Dlg and Lgl colocalize in a similar pattern. (C) Targeting chimeric CD8-Fas2 to BCs does not change Fas2 polarity (leading-to-trailing polarity ratio: 6.1±2.0; anti-Fas2 antibody partially recognizes also CD8-Fas2). (E-E') Fas2 mosaic, in which one PC has no Fas2. The PCs and cluster are turned perpendicular to the normal orientation for initiating movement, with the Fas2⁺ PC oriented in the direction of migration (arrow in E', compare with A'). High Fas2 level between PCs is lost (E, arrow, compare with A). Leading-to-trailing Fas2 polarity ratio is 6.8. (E') Dlg has cortical localization in BCs that contact the Fas2⁺ PC, but is mislocalized in the BC in contact with the Fas2^null PC (outline). Lgl shows the same distribution (inset, E), indicating that Fas2 signals maintenance and localization of Dlg and Lgl in BCs. (F-F'') Fas2 mosaic epithelium (at the time of BC delamination). Dlg and Lgl levels, and localization are similar in both Fas2⁺ and Fas2^null follicle cells. In Fas2⁺ follicle cells, Fas2 is lost from the membranes that contact Fas2^null cells (arrowheads), but remains at the site where they contact Fas2⁺ cells (arrows). (G) A late stage 7 Fas2 mosaic, in which loss of Fas2 from the presumptive BC epithelial cell (pBCs) causes loss of Fas2 from the membrane of the adjacent Fas2⁺ PC (arrowheads). (H) In an early stage 8 Fas2 mosaic, Fas2 is present in the PC membrane (arrowheads) adjacent to a Fas2^null BC. This suggests the presence of a Fas2 receptor in stage 8 BCs (see text).

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