It should be kept in mind that the most terminal aspects of the embryo are fated to become gut endoderm.
Gastrulation is the defining event of gut morphogenesis.
The gut is enshrouded in mesoderm which forms vascular musculature around the gut, and is also responsible for creating the gastric ceca. Overlying mesoderm communicates with the gut by secreted factors and through contact. Dpp has a prime function during endoderm induction in Drosophila. To achieve this, Dpp locally elevates the endodermal expression levels of Drosophila D-Fos with which it cooperates to induce lab . Dpp and Wg up-regulate vein expression in the midgut mesoderm in two regions overlapping the Dpp sources.