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Fig. 4. Bulk endocytosis of DSL ligands is not impaired in the absence of Lqf. (A) Clones of lqf^- cells (marked by cell surface CD8-GFP, green) in the eye disc stained for endogenous Dl (red) and expression of a Dl-lacZ transgene (blue). Undifferentiated cells (left) are recruited to form photoreceptors as they enter the morphogenetic furrow; the arrow marks a lqf^- clone in the vicinity of the furrow. Expression of Dl on the apical surface is strongly enhanced in the clone, as is expression of the Dl-lacZ reporter gene (shown at a deeper plane of section to visualize ß-Gal, which is nuclear). (B) As in A, except both Dl and ß-Gal staining are shown at deeper planes of section. Note that Dl staining within the clone is punctate, consistent with localization in endocytic compartments. (C) Clone of lqf^- cells (marked by CD8-GFP, green) in the wing blade primordium stained for endogenous Dl (red). The focal plane is at the apical surface in C, and approximately 6 µm beneath the apical surface in C' and C''. Dl appears to be generally unaffected by the lqf^- clone at both planes of focus; note the presence of cytosolic puncta at the deeper plane both inside and outside of the clone. The clone is located just dorsal to the DV boundary, and interrupts the normal, Notch-dependent upregulation of Dl in cells flanking the boundary. The same result was obtained with clones of either lqf¹²²⁷ or lqf^ARI cells; a lqf^ARI clone is shown. (D) Clone of hrs^- wg^- wing cells overexpressing an HRP-tagged form of Dl (^HRPDl), stained for HRP (green) and Wg (red). The clone (marked by ^HRPDl expression) is located close to the DV boundary, the source of Wg (at the top of the image). ^HRPDl and Wg co-localize in large puncta. Because these cells are wg^-, the Wg protein that co-localizes with ^HRPDl serves as an in vivo marker for an endocytic compartment, presumably the abnormal endosomal structures that result from the loss of Hrs. (E) As in D, except the clone is triply mutant for hrs^- wg^- and lqf^-. Note that ^HRPDl and Wg still co-localize, indicating that ^HRPDl has been internalized, like Wg, into the abnormal Hrs-deficient endosome.

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