Fig. S1.

PSI protein is a nuclear protein and is expressed broadly in the nervous system of Drosophila larvae and embryos. (A) Immunostaining of endogenous PSI protein in an adult Canton S male brain. Samples are costained with the DNA-binding dye, DAPI. (B) Immunofluorescent staining and confocal imaging of endogenous PSI protein, costained with ELAV (a pan-neuronal marker) in a wild-type Canton S Drosophila third-instar larval brain. Shown are two single confocal planes of one brain lobe and an eye disk. White arrows indicate clusters of neuronal precursor cells. (C) Immunofluorescence staining and confocal imaging of endogenous PSI protein (costained with ELAV) in a Canton S Drosophila embryo. Ventral view, anterior is to the top. Two stacks of consecutive confocal planes are shown. (Magnification: A, 100×; B and C, 60×.)