Follicular epithelium differentiation and eggshell morphogenesis in Drosophila

In Drosophila melanogaster, the eggshell of a mature egg is characterized by specialized anterior structures such as the micropile that allows sperm entry, the operculum that forms the exit hatch for the developed embryo, and two dorsal respiratory appendages. The complex architecture of the eggshell implies the underlying differentiation of the follicular epithelium in distinct spatial cell domains, each endowed with specific functions. The patterning of the follicular epithelium is achieved through an elaborate process that involves exchanges of information between the oocyte and the surrounding epithelial cells, as well as paracrine signaling within follicle cells. From our data it appears that Dpp and Egfr signaling pathways controls eggshell morphogenesis also by regulating the expression of eggshell structural genes. Interestingly, the exquisite temporal and spatial regulation of the VM32E eggshell structural gene, partly mediated by the Egfr and Dpp signaling system suggests a crucial role of VM32E protein in the complex process of eggshell assembly.