Temporal expression pattern of XLG transgenic flies. Males carrying the XLG construct (lines XLG-A and XLG-B) each with per⁺ (A) orper⁰¹ (B) were sectioned and stained with anti-β-GAL. A, In XLG-A, only weak cytoplasmic staining in the PRs is visible at ZT9. Scale bar, 40 μm. At ZT21, prominent staining in the LN_v(arrows) is detectable, whereas staining in PRs seems only slightly increased compared with ZT9 and is mainly cytoplasmic. Glia staining at this high time point is just above the limit of detection. Magnification is as at ZT9. For the XLG-B line, similar expression patterns were observed. In LN_v at ZT9, the signal was barely detectable (solid arrow), whereas prominent staining of the dorsal group of LNs (LN_d) appears at ZT21 (open arrow). Scale bars: ZT9, 25 μm; ZT21, 12.5 μm. B, In theper⁰¹ background, no XLG-A-mediated expression was detectable in LNs and glia at ZT9. As inper⁺, there was only weak cytoplasmic PR staining at this time point. At ZT21, strong staining in the LN_v (arrows) as well as in glia and PRs is visible. Magnifications are the same as for XLG-A (per⁺). For the XLG-B line, similar signal fluctuations were observed, although weak staining of the LN_d (open arrow) was detectable at ZT9. Thesolid arrow at ZT21 points to a group of LN_vshowing strong expression of the XLG-B fusion protein. Magnifications are as in XLG-B (per⁺) at ZT9.