Figure 5. Odd does not repress prd transcription until phase 3.
Relative expression of prd and odd is shown in a late phase 2 embryo (just prior to frequency doubling) and an early phase 3 embryo (showing the first signs of frequency doubling). (A, B) Whole embryos, lateral view, anterior left, dorsal top. Individual channels are shown to the right of each double-channel image, in the same vertical order as the panel label. (C, D) Blow-ups of expression in stripes 2–6; asterisks mark the location of odd primary stripes. Thresholded images (C’, D’) highlight regions of overlapping expression (yellow pixels). Considerable overlap between prd and odd expression is observed at phase 2 but not at phase 3. Note that the prd expression pattern is the combined result of initially broad stripes of medium intensity, and intense two-cell wide 'P' stripes overlapping the posterior of each of the broad stripes (arrowheads in C’’’, D’’’). The two sets of stripes are mediated by separate stretches of DNA (Gutjahr et al., 1994), and must be regulated differently, since the 'P' stripes remain insensitive to ectopic Odd even during phase 3 (Saulier-Le Dréan et al., 1998; Goldstein et al., 2005). Scale bars = 50 μm.