A cluster of early eggshell protein genes in Drosophila melanogaster: Gene structure, expression and regulation

The formation of the insect eggshell is a popular model system in which to study molecular mechanisms involved in the production of complex structures. The eggshell, secreted by ovarian follicle cells during the later stages of oocyte maturation, is deposited in several layers. The vitelline membrane is deposited during stages 8-10, and the several layers of the chorion are secreted during stages 11-14. We are examining the expression of early eggshell genes. I have characterized a cluster of follicle cell specific genes expressed during the period of vitelline membrane formation in Drosophila. Four genes are clustered in 8 kilobase pairs of genomic DNA from the 26A region of the second chromosome. Three of these genes encode 700 nucleotide long RNAs; the two most abundantly expressed code for major vitelline membrane proteins. Hybrid selected translation and sequencing studies suggest the product of the third gene is a minor eggshell protein. The fourth gene of the cluster specifies a 1400 nucleotide RNA of unknown function. The direction of transcription, intron-less structures and positions of these genes have been determined by northern blot analysis and S1 protection studies. Northern blot analysis demonstrates that these genes are expressed specifically in the female\u27s ovary and are only detected in eggchambers of stages producing vitelline membrane. The follicle cell specific expression of these genes has been demonstrated by in situ hybridization to ovarian tissue sections or by S1 protection studies with RNA isolated from follicle cell or nurse cell fractions of cut stage 10 eggchambers. Gel electrophoresis-DNA binding studies with nuclear proteins isolated from expressing tissue have identified two potential cis-regulatory regions of one of the major vitelline membrane protein genes. One region is 5$\sp\prime$ to the gene, between $-$146 and $-$53; the second region is within the transcribed portion of the gene, upstream of +153. The location of the 5$\sp\prime$ region is similar to that of elements required for proper tissue and temporal specificity of both early and late chorion protein genes