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Fig. 5. Integration of prepatterning and lateral inhibition functions via Wnt
and Notch signalling in Drosophila. In the epidermis of the
imaginal disc of Drosophila, a combination of history and spatial
patterning delimits clusters of cells (shown at the bottom) that can undergo
neural specification through the expression of members of the Achaete-Scute
complex (AS-C, blue). (A) AS-C expression is promoted by Wingless
signalling and is antagonized by Notch (see text for details) in a manner that
is independent of its transcriptional effector, Suppressor of Hairless
[Su(H)], but depends on the activity of the ubiquitin ligase Deltex.
(B) The binding of Wingless to its receptor complex triggers the
activation of Armadillo/β-catenin and the suppression of the antagonistic
activity of Notch, probably via Dishevelled. In consequence, all cells within
the proneural cluster begin to express members of the AS-C. (C) One
cell in the cluster (darker blue) begins to express higher levels of AS-C
proteins than the other cells and, as a consequence, takes the lead in the
process of `lateral inhibition', by which Notch signalling via Delta leads to
the generation of free NICD and through Su(H) represses the expression of the
AS-C genes.
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