ZAM particles accumulate along the apical end of the follicle cells when the yolk protein receptor yl is mutated. A, a stage 9 ovarian chamber from a Drosophila female fly heterozygous for yolkless sectioned along the posterior pole to show those columnar follicle cells that are expected to express ZAM viral particles (Scale Bar, 1 μm). B, numerous presumptive ZAM viral particles, some of which are heavily gold-labeled following exposure to anti-gag antibodies, are visible along the apical end of a follicle cell and in close association with secretory granules containing the vitelline membrane precursors (Scale Bar, 200 nm). C, an abnormally shaped yolk granule in the cortical ooplasm of yl oocytes. Note that this granule has neither a superficial layer nor any ZAM viral particles associated (Scale Bar, 500 nm). D, an alpha 2 yolk granule from a stage 10 ovarian chamber of a yl- fly (scale bar, 500 nm). Fc; follicle cells; Vm: vitelline membrane; y: yolk granules; α2: alpha 2 yolk granule.