GATA factor genes in the Drosophila midgut embryo.

The Drosophila GATA factor gene serpent (srp) is required for the early differentiation of the anterior and posterior midgut primordia. In particular, srp is sufficient and necessary for the primordial gut cells to undertake an epithelial-to-mesenchimal transition (EMT). Two other GATA factor genes, dGATAe and grain (grn), are also specifically expressed in the midgut. On the one hand, dGATAe expression is activated by srp. Embryos homozygous for a deficiency uncovering dGATAe were shown to lack the expression of some differentiated midgut genes. Moreover, ectopic expression of dGATAe was sufficient to drive the expression of some of these differentiation marker genes, thus establishing the role of dGATAe in the regulation of their expression. However, due to the gross abnormalities associated with this deficiency, it was not possible to assess whether, similarly to srp, dGATAe might play a role in setting the midgut morphology. To further investigate this role we decided to generate a dGATAe mutant. On the other hand, grn is expressed in the midgut primordia around stage 11 and remains expressed until the end of embryogenesis. Yet, no midgut function has been described for grn. First, here we report that, as for dGATAe, midgut grn expression is dependent on srp; conversely, dGATAe and grn expression are independent of each other. Our results also indicate that, unlike srp, dGATAe and grn are not responsible for setting the general embryonic midgut morphology. We also show that the analysed midgut genes whose expression is lacking in embryos homozygous for a deficiency uncovering dGATAe are indeed dGATAe-dependent genes. Conversely, we do not find any midgut gene to be grn-dependent, with the exception of midgut repression of the proventriculus iroquois (iro) gene. In conclusion, our results clarify the expression patterns and function of the GATA factor genes expressed in the embryonic midgut.