Fig. 9. (A-C) Analysis of SOP development in the notum of PsnC1
HE31 double mutant wing imaginal discs. Anterior is towards
the left, ventral is to the bottom. Expression of Sens is revealed by antibody
staining. (A) Expression of Sens is strongly reduced or absent in the
PsnC1 HE31 double mutant proneural clusters.
(B) The cells of the double mutant clusters still express the SOP-E (arrows),
indicating that they are present. (C) The same disc as in A and B, showing
expression of the SOP-E in green and of Sens in red. The analysis indicates
that, in the double mutant discs, SOP development arrests in a similar manner
as in Su(H) mutants. (D,E) Expression of UAS Su(H)VP16 with
dppGal4 in wing imaginal discs of the late third larval instar stage.
(D) Expression of sens. Expression of Sens is lost in most SOPs of
the notum. Compare with Fig. 2E
for normal expression of sens. The arrow indicates ectopic expression
of Sens in the wing area, which is a result of the ectopic induction of the
wing margin and bristles by UAS Su(H)VP16
(Klein et al., 2000; Furriols
et al., 2000). (E) Expression of UAS GFP in a disc of the same genotype as in
D, showing that the expression of dppGal4 has expanded over most of
the notum. (F) A PsnC1 mutant wing imaginal disc where UAS
Su(H)
H is expressed with scaGal4. The discs is
stained by anti Hnt antibody staining. No expression of Hnt is observed in the
region of the notum. (G) The same disc as in F showing expression of Hnt in
red and of GFP in green. The expression of the GFP marks the cells of the
proneural clusters. This result shows that although the cells of the clusters
are present, they fail to develop to the stage at which Hnt expression is
initiated. Thus, the expression of UAS Su(H)H result in an
arrest of SOP development in a similar manner as in Psn H double
mutants. (H) Summary of the results shown in this picture. The results suggest
that Su(H) suppresses the expression of a negative regulator of sens.
For this function, Su(H) requires the presence of H. Recent evidence by Barolo
et al. (Barolo et al., 2002)
indicates that H acts as a bridge between Su(H) and its co-repressors Groucho
(Gro) and CtBP. It is likely that Gro and CtBP are also part of the repressor
complex required for the proper expression of sens.