DIFFERENT SIGNALING PATHWAYS CONTROL VM32E GENE EXPRESSION IN THE FOLLICLE CELLS

Eggshell morphogenesis is a complex process that depends on various factors. Coordinated expression of the eggshell structural genes is one of these. Little is known about the signaling pathways and the transcription factors that are involved in this process. From our previous studies a role has emerged for the Decapentaplegic (DPP) pathways in the transcriptional regulation of the VM32E gene, which encodes one of the most abundant vitelline membrane protein. DPP represses VM32E expression in the centripetal cells acting on the -253/-113 region of VM32E promoter. Our recent work has shown that the Epidermal Growth Factor Receptor (EGFR) signaling modulates VM32E transcription in the main body follicle cells. This control is executed on the -112/-39 VM32E promoter region and it involves the activity of PointedP2 ETS transcription factor. We also found that VM32E expression is under hormonal control. Clonal analysis of the usp2 null allele reveals that VM32E expression in the main body follicle cells is positively regulated by usp protein. As in other cases, it seems that this promoting activity does not require USP DNA binding domain, since in follicle cells homozygous for the usp3 allele VM32E transcription is not altered. Using RNAi to induce the silencing of the Ecdysone receptor (EcR) gene we also demonstrated that the EcR-B1 isoform is necessary for VM32E expression, suggesting that an EcR-B1/USP complex activates VM32E transcription in the main body follicle cells.