Fig. 5. The epistatic relationship between her1 and the notch pathway changes along the anteroposterior axis of the PSM. Anterior is upwards. (A-G) her1 expression is in blue and that of myoD is in red. (A) In wild-type embryos, stripes of her1 expression are seen throughout the PSM. This embryo is a sibling of the mutant aei/deltaD^AR33 embryo shown in B. In aei/deltaD embryos, no stripes of her1 expression are observed, and her1 is always exclusively expressed in a ‘salt and pepper’ pattern in the anterior PSM (between the broken lines). (C) her1 stripes form in fss^AE114 embryos, but expression in the anterior PSM is always lost. (D) A fss^AE114;aei/deltaD^AR33 double mutant sibling of the embryo shown in C. In fss;aei/deltaD double mutant embryos, no stripes of her1 expression are formed (as in aei/deltaD embryos) and there is no expression of her1 in the anterior PSM (as in fss embryos). (E) Injection of deltaC^mo1 into fss^AE114 embryos produces a pattern of her1 expression similar to that observed in fss;des/notch1 and fss;aei/deltaD double mutant embryos: no stripes of expression are formed and no expression is seen in the anterior PSM (four experiments; n=123; 99% affected). (F) fss^AE114;bea^M98B double mutant embryos also lack both stripes of her1 expression and expression in the anterior PSM. These embryos were derived from a cross between double homozygous parents. (G) Injection of her1^mo1 into fss^AE114 embryos produced a her1 expression pattern identical to that of her1^mo embryos (three experiments; n=158; 99% affected). A parallel analysis of deltaC expression yielded similar results (not shown). (H-N) All panels show deltaC expression. (H) deltaC expression in wild-type embryos. (I) her1^mo1 embryos (four experiments 72% of 97 embryos) exhibit a refining stripe within the deltaC expression domain in the anteriormost PSM, arrow. In her1^mo1;fss^AE114 embryos (J) (two experiments 0% of 184 embryos), her1^mo1;aei/deltaD^AR33 embryos (K) (four experiments 0.5% of 202 embryos), her1^mo1;notch1^mo1 embryos (L) (three experiments 0.7% of 153 embryos), her1^mo1; deltaC^mo1 (M) (three experiments 0.6% of 169 embryos) and her1^mo1; bea^M98B (N) (two experiments 1% of 86 embryos), this refining stripe is lost. Sometimes in these double mutant embryos the pattern (stripe) of repression is converted into a ‘salt and pepper’ pattern, arrowheads in K-M.