Eggshell Assembly in Drosophila: Processing and Localization of Vitelline Membrane and Chorion Proteins

Abstract

The Drosophila eggshell consists of three major proteinaceous layers: the vitelline membrane, the inner chorionic layer, and the outer endochorion. During the latter stages of oogenesis, the proteins that comprise these layers are synthesized and secreted by epithelial follicle cells which surround the maturing oocyte. While there is considerable knowledge of the structural units which comprise the eggshell layers, there is little knowledge of how individual proteins function or interact with one another to form the structure. Immunoelectron microscopy was used to follow the distribution of four different eggshell proteins in the assembling and mature eggshell. sV23 and sV17, follicle cell proteins synthesized during the early stages of eggshell formation (stages 8-10), were distributed within the vitelline membrane layer at all stages. Despite marked temporal differences in their accumulation profiles, s36 and s18, putative chorion proteins, were similarly distributed throughout the floor, pillars, and roof of the endochorion. Although the vitelline membrane appears to be morphologically complete by stage 11, developmental Western blots and immunolocalization data indicate that molecular dynamism persists within the layer throughout the subsequent choriogenic stages. During early chorion formation the vitelline membrane appears to act as a reservoir for chorion proteins since s36 was found predominantly in the vitelline membrane layer of stage 12 egg chambers. During the late choriogenic stages (13-14), both sV17 and sV23 are processed to smaller derivatives. Interactions between the eggshell layers were suggested by ultrastructural analysis of a sV23 protein null mutant which showed that the structural integrity of the outer chorion is dependent upon the presence of a vitelline membrane component.

Divergent transcriptomic responses to repeated and single cold exposures in Drosophila melanogaster

“…The Chorion proteins in the vitelline membrane layers play important roles in the assembly and stabilization of the mature eggshell (Noguerón et al, 2000). As vitelline membrane proteins are usually synthesized during the early stages of eggshell development, whereas chorion proteins are synthesized in later stages (Pascucci et al, 1996), cold exposure appears to affect multiple stages of egg development, which could account for at least some of the effects of cold on reproduction. It is unclear whether the upregulation of egg-related genes reflects the repair or replacement of eggs damaged by cold or another role in modifying reproductive output.…”

Cadherin Cad99C is required for normal microvilli morphology in Drosophila follicle cells

“…Ovaries dissected from adult flies were fixed and stained with the following primary antibodies: polyclonal rabbit anti-Cad99C, 1:10,000 (Schlichting et al, 2005); polyclonal rabbit anti-sV17, 1:1000 (Pascucci et al, 1996); polyclonal rabbit antisV23, 1:10,000 (Pascucci et al, 1996); polyclonal rabbit anti-S18, 1:1500 (Pascucci et al, 1996); polyclonal rabbit anti-S36, 1:1000 (Pascucci et al, 1996); rat anti-DEcadherin (DCAD2), 1:100 (Oda et al, 1994); and monoclonal mouse anti-GFP, 1:2000 (8362-1; Clontech). Secondary antibodies, all diluted 1:200, were goat anti-mouse Alexa Fluor 488, goat anti-rabbit Alexa Fluor 488, goat anti-rabbit Alexa Fluor 594 (Molecular Probes), and donkey anti-rat (712095153; Jackson ImmunoResearch).…”

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

“…Another example is provided by the early chorion protein s36, which initially localizes mainly in the vitelline membrane layer and, at late stages, it becomes distributed throughout the endochorion (Pascucci et al, 1996). Although s36 is described as a chorion protein and its mutant as producing egg chambers that lack endochorion organization (Digan et al, 1979), the mutant eggs show defects also in the vitelline membrane assembly ).…”