The role of Dpp and its inhibitors during eggshell patterning in Drosophila
2007
The Drosophila eggshell is patterned by the combined action of the
epidermal growth factor [EGF; Gurken (Grk)] and transforming growth factorβ
[TGF-β; Decapentaplegic (Dpp)] signaling cascades. Although Grk
signaling alone can induce asymmetric gene expression within the follicular
epithelium, here we show that the ability of Grk to induce dorsoventral
polarity within the eggshell strictly depends on Dpp. Dpp, however, specifies
at least one anterior region of the eggshell in the absence of Grk. Dpp forms
an anteriorposterior morphogen gradient within the follicular epithelium and
synergizes with the dorsoventral gradient of Grk signaling. High levels of Grk
and Dpp signaling induce the operculum, whereas lower levels of both pathways
induce the dorsal appendages. We provide evidence that the crosstalk between
both pathways occurs at least at two levels. First, Dpp appears to directly
enhance the levels of EGF pathway activity within the follicular epithelium.
Second, Dpp and EGF signaling collaborate in controlling the expression of Dpp
inhibitors. One of these inhibitors is Drosophila sno (dSno ), a
homolog of the Ski/Sno family of vertebrate proto-oncogenes, which synergizes
with daughters against dpp and brinker to set the posterior
and lateral limits of the region, giving rise to dorsal follicle cells.
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