Genetic Dissection of Eggshell Assembly in D. melanogaster. D.K. Mauzy-Melitz , J.C. Badciong , G.L. Waring. Department of Biology, Marquette University, Milwaukee, WI 53233.

   The Drosophila eggshell is a specialized extracellular matrix that forms between the oocyte and overlying follicle cells during the late stages of oogenesis. The dec-1 gene encodes multiple proteins important for eggshell assembly. The three dec-1 proproteins, fc106, fc125, and fc177 are cleaved extracellularly in the vitelline membrane producing at least five distinct mature products. Analysis of induced and engineered dec-1 mutations have demonstrated the functional importance of the mature products. The distinct spatial distributions of each of the dec-1 derivatives and the different morphological phenotypes of loss of function mutations suggest that each dec-1 product plays a distinct role in eggshell assembly. dec-1 null mutants produce a disorganized endochorion which eventually collapses into the underlying vitelline membrane layer. By introducing genetically engineered mutant dec-1 transgenes into a variety of dec-1 genetic backgrounds, we have generated flies that produce nonfunctional eggshells which display a range of morphological defects. Some mutant transgenes resulted in eggshells that were indistinguishable from dec-1 null mutants, others resulted in eggshells that were wild type in appearance. Phenotypic effects of some of the transgenes suggest that some derivatives play a prominent role in organizing the chorion layer while others are essential for its stabilization. Dominate negative effects were associated with small deletions that led to the accumulation of dec-1 processing intermediates. (Supported by NIH grant R15 GM55952).