Genetic dissection of eggshell assembly in Drosophila melanogaster
Abstract
The Drosophila eggshell is a specialized extracellular matrix formed between the oocyte and the follicle cells during the later stages of oogenesis. One of the genetically identified eggshell structural genes, dec-1 , encodes multiple proteins important for eggshell assembly. The three dec-1 proproteins, fc106, fc125, and fc177 are cleaved in the extracellular space producing at least five distinct mature products. Analyses of induced and engineered dec-1 mutations have demonstrated the functional importance of the mature products. A derivative of each of the proproteins is important in eggshell morphogenesis as assayed by fertility and structural morphology. The spatial distribution of the products suggests each have a distinct function. A derivative of fc106 localizes to the inner chorionic layer, another to the endochorion and vitelline membrane. A C-terminal derivative of fc177 localizes to the spaces or cavities between the electron dense material in the endochorion and dorsal appendages. An N-terminal derivative of fc177 localizes to the electron dense structures of the dorsal appendages. Other derivatives of dec-1 proproteins localize to the oocyte and vitelline membrane. All of the derivatives initially localize to the vitelline membrane and then, depending on the stage of oogenesis, redistribute to other regions of the eggshell. Electron Micrographs of mutant eggshells reveal abnormalities consistent with the localization data. The morphologies range from near wild type structures to eggshells where the endochorion has collapsed into the vitelline membrane. One of the proproteins, fc177 was found to be critical in the assembly of the endochorion structures. Furthermore, the collapse can occur after a reasonable normal endochorion structure has been formed suggesting a role for some of the other dec-1 derivatives in stabilizing the eggshell. A model is presented for the assembly of the mainshell endochorion and the dorsal appendages.
This paper has been withdrawn.