Fig. 2. Bgb and Run expression in the eye imaginal disc. Posterior is to the left. Arrow indicates the position of the furrow. (A-C) Wild-type eye disc stained with -Bgb antibody. (A) At the basal level, nuclear staining is seen in the undifferentiated pool of cells. This staining begins immediately posterior to the furrow. (B) At a slightly more apical level, Bgb protein is seen in the nuclei of the R8, R1 and R6 cells. The expression of Bgb in the R8 cell initiates within 1 column of the furrow, while the expression in R1 and R6 initiates about 4 columns posterior to the furrow. (C) At the most apical focal plane, cone cells (cc) and the R7 cell express Bgb beginning about 7 columns posterior to the furrow. The R7 cell expresses Bgb at a much higher level than in any of the other cells. (D,E) Wild-type eye disc stained with -Run antibody. (D) Run protein is detected in the nuclei of the R8 cell, initiating 1 column posterior to the furrow. Run expression was determined to be in R8 by the central location of this cell within an ommatidial cluster and through co-localization with the R8 specific marker, Boss (Kramer et al., 1991 and data not shown). (E) Run expression is seen in R7 about 7 columns posterior to the furrow. The timing of Run expression in R7 and R8 correlates well with the expression pattern of the Bgb protein in these cells. (F,G) Bgb expression in a lz^77a7 background. lz^77a7 is an eye-specific null allele of lz (Flores et al., 1998). (F) Bgb expression is limited to the R8 cell. (G) R7 expression of Bgb is absent. (H) Bgb expression in a lz^sprite background. With this gain-of-function allele, lz is misexpressed in R3 and R4 (Daga et al., 1996). Arrowheads indicate a corresponding ectopic expression in R3 and R4 of the Bgb protein. (I-J) Run expression in a lz^77a7 background. (I) Run expression in lz^77a7 is seen only in the R8 cell. (J) At the slightly higher R7 focal plane, no Run staining is observed in the R7 cell. (K,L) S2 cells stained with -Bgb. (K) In cells transiently transfected with Bgb, the majority of the Bgb protein is found in the cytoplasm. (L) When Bgb and lz are co-transfected, the majority of Bgb protein moves to the nucleus. (M,N) S2 cells stained with -Lz. (M) In cells transiently transfected with lz cDNA, Lz protein is seen in the nucleus. (N) Cotransfection of Bgb and lz does not affect the localization of Lz protein.