Building up the Drosophila eggshell:: First of all the eggshell genes must be transcribed

The Drosophila eggshell provides a model system for studying the assembly of extracellular matrix. Eggshell formation is a complex process that requires time-coordinated synthesis, cleavage, and transport of various proteins and finally cross-linking mediated by particular functional domains. It has been suggested that the eggshell can act as a storage site for spatial cues involved in embryonic pattern formation. Its structural components are synthesized in the somatic follicle cells in a precise temporally and spatially regulated manner. This review will summarize our knowledge of eggshell gene expression. We will discuss the amplification of the chorion gene clusters and the data acquired on the expression patterns and the regulatory elements controlling transcription of eggshell genes. We will then focus on the findings that correlate follicular epithelium patterning and eggshell gene expression, and discuss the interesting perspectives of an involvement in eggshell assembly of embryonic patterning cues.