Fig. 5. dMyc is a dose-dependent regulator of follicle cell and nuclear size. (A) An overlay of DAPI/hGFP images shows a large clone of dm² follicle cells with nuclei of unusually small size. (B-D) DAPI (B), hGFP (C) and merged (D) images of a field of follicle cells with a clone of dm²/dm² mutants (yellow outline) and twin-spot derived +/+ cells (white outline). The nuclei of +/+ cells (carrying two copies of the hGFP gene and therefore distinguishable from dm²/+ cells by their increased fluorescent intensity) are larger than the nuclei of their dm²/+ sister cells, which are larger than the nuclei of the dm²/dm² mutant cells. (E) Measurement of the area of nuclei indicates that homozygous wild-type nuclei are twice the size of dm²/+ nuclei, and tenfold larger than the nuclei of dm²/dm² mutant cells. See Materials and methods for details on size determination. (F) A DAPI-stained follicle at stage 5, prior to the time at which follicle cell endoreplication initiates. (G) At higher magnification, the lack of hGFP nuclear staining (white outline) indicates the position of a clone of dm²/dm² mutant follicle cells. (H) Anti-Fas III staining, which weakly stains the periphery of all follicle cells, demonstrates that the homozygous mutant cells (asterisks) are considerably smaller than the neighboring follicle cells. Thus, dMyc regulates follicle cell growth prior to the onset of endoreplication.