Fig. 3.

Ph and Pc are required to compact repressed BX-C before ectopic Hox gene transcription. a–c; g–i Box plots displaying distributions of the distances Ubx–AbdB (a, g), abdA–AbdB (b, h), Ubx–abdA (c, i), in the head-PS0 (a–c), and in PS2–PS4 (g–i) during early and late embryogenesis. Distances were measured in the cell nuclei of ph^del embryos (red) and their respective controls (dark gray) or Pc^XT109 embryos (green), and their respective controls (light gray). Distance distributions are comprised between 0 and 1.5 µm and the lower and upper bounds of the colored rectangles correspond to the first and third quartiles, whereas the middle bars show the median distances. The black lines indicate significant differences between the mutants and their respective control embryos (Mann–Whitney U-test, two-tailed, *P < 0.05; **P < 0.01; ***P < 0.001). d–f; j–l Difference between the median distances Ubx–AbdB (d, j), abdA–AbdB (e, k), Ubx–abdA (f–l) measured in ph^del and the same distances measured in its control embryos (red) or in Pc^XT109 and its control embryos (green), during embryonic development in head-PS0 (d–f) and PS2–PS4 (j–l). Arrows indicate when a Hox gene is firstly ectopically expressed in ph^del (red) or Pc^XT109 (green) embryos. m Schematic linear representation of BC-X showing the DNA FISH probe positions. n–p Plots of the three median distances corrected for chromatic aberrations, between the promoters of Ubx, abdA, and AbdB. Comparison of the effects of Ph and Pc on the folding of BX-C during early (n) and late embryogenesis (o) with the openings induced by Hox gene transcription (p). Scale bar, 100 nm