SLOB is expressed prominently in photoreceptor cells and PI neurons. (A) Head frontal section from y w (wild type) flies immunostained for SLOB protein. SLOB is expressed in the nuclei of the photoreceptor cells. (B) Brain wholemounts from y w flies immunostained for SLOB protein. SLOB is expressed prominently in the PI neurons of the protocerebrum (box), as well as elsewhere in the brain. (C) Enlargement of the boxed area in (B) to illustrate the cytoplasmic localization of SLOB in the PI neurons. Typically 6–8 PI neurons are SLOB positive. (D-G) GAL4 flies, specific for the three subsets of PI neurons, were crossed to UAS-GFP flies and immunostained for SLOB. (D) Mai 301 GAL4 is expressed in PI-1 neurons , shown by GFP expression. UAS-GFP tends to have a nuclear localization. SLOB positive PI neurons are immunostained with Texas Red, and SLOB has a cytoplasmic expression pattern. SLOB does not localize within PI-1 neurons. (E) Kurs 58 GAL4 is expressed in PI-2 neurons. SLOB is not found within the PI-2 neurons. (F) Mai 281 GAL4 is expressed in two of the three subsets of PI neurons (PI-2 and PI-3). SLOB is localized within some of these PI neurons and because SLOB was not found within PI-2 this suggests that the SLOB positive subset is PI-3. (G) Kurs 45 GAL4 is expressed only in PI-3 neurons. SLOB positive cells colocalize with the GFP expressing PI-3 cells. (H) Brain wholemount from y w flies highlighting components of the circadian system – the small ventral lateral neurons (LNv), the dorsal lateral neurons (LNd), the dorsal neurons (DN1–3) and the pars intercerebralis neurons (PI). The wholemount was immunostained for SLOB, PER and PDF. The red component is PER staining; the green staining in the PI neurons corresponds to SLOB, and the green staining elsewhere is PDF. Previous staining in Pdf01flies reveals no PDF in the PI neurons (data not shown). PDF filled projections end close to, but appear to stop short of, the PI neurons. The projections of the DN (not visible) may synapse on the PI neurons.