Drosophila dec-1 eggshell proteins are differentially distributed via a multistep extracellular processing and localization pathway

In Drosophila the multilayered eggshell forms during late oogenesis between the oocyte and the overlaying follicle cells. Proper eggshell assembly req uires wild-type dec-1 gene function. Alternatively spliced dec-1 transcript s encode three proproteins that are cleaved extracellularly in a stage-spec ific manner to at least five distinct derivatives. Using polyclonal antibod ies raised against fusion proteins containing different regions of the dec- 1 proteins, we have localized several dec-1 derivatives in the assembling a nd completed eggshell. Although all of the dec-1 derivatives are generated in the oocyte proximal vitelline membrane layer, they are differentially di stributed in the mature egg. Some derivatives are gradually released from t he vitelline membrane and become localized within distinct regions of the c horion, while others are taken up by the oocyte or become concentrated in t he endochorionic spaces or cavities. The diverse distributions of the dec-1 derivatives suggest that each derivative plays a distinct role in eggshell assembly. These results also suggest that the vitelline membrane layer, by acting as a transient storage site, may control the availability of molecu les active in eggshell assembly and by extension perhaps other follicle cel l products important in early embryonic pattern formation. (C) 2000 Academi c Press.