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Fig. 7. Kul is required for unidirectional Notch signaling at the wing margin.
(A,C) In wild-type wing discs, Cut and Wg are expressed by the two rows of
wing margin cells. (B,D) Expression of ds-kul by sd-GAL4,
which is broadly expressed in the wing pouch, gave rise to a reduced pouch and
loss or severe reduction of Cut and Wg expression (arrow). The adult wing (J)
was dramatically reduced in size and exhibited only a rudimentary wing margin
in very restricted domains (arrowhead). Arrow-wing hinge. (E,F)
ds-kul expression by sal-GAL4 gave rise to a reduction in Wg
expression. (G) In wt wing discs Dl is not detected at the wing
margin (arrowhead). (H,I) Expression of ds-kul in the sal
domain altered the distribution of Dl, which accumulated also in the wing
margin (arrowhead), and expanded beyond the normal dorsal and ventral borders
of Dl expression at the juxta margin (arrow). This experiment demonstrates
that continuous cleavage of Dl by Kul is necessary for complete removal of the
protein in the margin. In the absence of Kul, residual levels of Dl
transcription give rise to accumulation of Dl, and lead to disruption of
unidirectional Notch signaling. (K) Scheme: in wild-type wing discs, the
margin cells express Wg and Cut, and suppress the expression of Dl.
Wg activates Dl and Ser expression in the juxta-margin cells. High levels of
Dl and Ser in these cells have a dominant-negative effect on Notch activation,
but activate Notch signaling in the margin cells. Thus, a stable signaling
loop is maintained. Elimination of Kul leads to the appearance of Dl in the
margin, and alleviation of Notch signaling due to the dominant-negative effect
of Dl.
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