Figure 7.

MMB/dREAM in olfactory organs and model for olfactory receptor expression. Confocal micrographs of antennae (A) and maxillary palp (B)s using anti-Mip120 and anti-Elav in wild-type flies (left panels), anti-E2F2 and anti-Elav in wild-type flies (middle panels), or anti-GFP and anti-Elav in myb promoter-GFP∷Myb flies (right panels). (C) Representative confocal micrograph from a Gr21a promoter-mCD8∷GFP antenna stained with anti-CD8, anti-Elav, and anti-Mip120 antibodies. Overlays of all three (left) and of anti-Elav with anti-Mip120 (right) are provided. Arrowheads indicate nuclei of Gr21a⁺ ab1C neurons. (D) Schematic showing cells that were selected for analysis of nuclear stain signal intensity and mean Myb, Mip120, or E2F2 signal intensity in ab1C or a neighboring nucleus as a ratio of the mean signal in the neighboring three cells. For Myb signal, n = 48 for neighboring cells and n = 16 for ab1C cells. For Mip120 signal, n = 70 for neighboring cells and n = 25 for ab1C cells. For E2F2 signal, n = 29 for neighboring cells and n = 13 for ab1C cells. Error bars indicate SEM. (*) P < 0.05; (***) P < 0.001. (E) Olfactory receptors have a H3K9me2-repressive chromatin mark (red dashed line). Expression of Gr63a/Gr21a receptors in the ab1C neurons of antennae requires Myb (green arrow), and Myb opposes histone methyltransferase Su(var)3-9. Conversely, repression of Gr63a in other sensory organs and the brain requires Mip120 and E2F2 (combined red and orange line). The absence of Mip120 or E2F2 causes misexpression and increased H3K4me3 chromatin mark at Gr63a gene (green dashed arrow). E2F2 also has a repressive modulatory effect on Gr63a expression in ab1C cells (solo red line), while Mip130 represses expression of an unknown olfactory receptor in the antenna (dark-orange line).