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Fig. 8. A refined model for the roles of EGFR signalling in embryonic epidermal
patterning (see Discussion). A lateral cross section of a part of the ventral
epidermis is depicted with smooth-cuticle cells in white and
denticle-secreting cells and denticles in black. The
rhomboid-1-expressing cells that act as the source of cleaved Spitz
are depicted with green nuclei, while cells that are the source of the
Wingless signal have blue nuclei. Arbitrary levels of EGFR signalling versus
two thresholds for the observed phenotypes are shown above the cells. Mutation
of spitz group genes (red curve) results in apoptosis of
smooth-cuticle cells when the levels of EGFR signalling fall below a
threshold, and this is manifest as a denticle belt fusion. Reducing signalling
further (for example, by removing the EGFR, black curve) results in denticle
belt fusions and failure of denticle fate specification
(Szüts et al., 1997).
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