RESUMEN
A study was made of the localization and assembly of the VM32E protein, a putative vitelline membrane component of the Drosophila eggshell. The results highlight some unique features of this protein compared with the other proteins of the same gene family. At the time of its synthesis (stage 10), the VM32E protein is not detectable in polar follicle cells. However, it is able to move in the extracellular space around the oocyte and, by stage 11 is uniformly distributed in the vitelline membrane. During the terminal stages of oogenesis the VM32E protein is partially released from the vitelline membrane and becomes localized in the endochorion layer also. By analyzing transgenic flies carrying variously truncated VM32E proteins, we could identify the protein domains required for the proper assembly of the VM32E protein in the eggshell. The highly conserved vitelline membrane domain is implicated in the early interactions with other components and is required for cross-linking VM32E protein in the vitelline membrane. The terminal carboxylic domain is necessary for localization to the endochorion layer. Protein with the C-end domain deleted is localized solely to the vitelline membrane and cross-linked only in laid eggs, as occurs for the other vitelline membrane proteins.
Asunto(s)
Proteínas del Huevo/genética , Oogénesis/fisiología , Membrana Vitelina/química , Membrana Vitelina/metabolismo , Secuencia de Aminoácidos , Animales , Animales Modificados Genéticamente , Western Blotting , Drosophila melanogaster , Epítopos/genética , Femenino , Microscopía Inmunoelectrónica , Datos de Secuencia Molecular , Mutación/fisiología , Estructura Terciaria de Proteína , Membrana Vitelina/ultraestructuraRESUMEN
Abstract. During the final step of Drosophila vitelline membrane formation, the structural proteins composing this layer become cross-linked by covalent bonds. In the present report, we analyzed the vitelline membrane cross-linking in mutants having defects either in this layer or in the chorionic layers. In the fs(1)Nasrat and fs(1)polehole mutant alleles conferring defects in vitelline membrane formation, disruption of vitelline membrane cross-linking was observed, indicating the involvement of these two genes in the process. On the contrary, in the fs(1)Nasrat and fs(1)polehole alleles showing defects only at the termini of the embryo the vitelline membrane is properly formed, confirming a multifunctional activity of their gene products. Altered vitelline membrane cross-linking was also detected in a mutant of the chorion protein gene Cp36and in the chorion amplification mutant fs(1)K1214, suggesting a role of the structural components of chorion layers in the process of vitelline membrane hardening.
Asunto(s)
Proteínas de Drosophila/genética , Drosophila melanogaster/genética , Proteínas del Huevo/genética , Proteínas de la Membrana/genética , Membrana Vitelina/fisiología , Animales , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/embriología , Drosophila melanogaster/fisiología , Proteínas del Huevo/metabolismo , Femenino , Proteínas de la Membrana/metabolismo , Mutación , Ovario/fisiología , Ovario/ultraestructura , Proteínas Proto-Oncogénicas c-raf , Membrana Vitelina/metabolismoRESUMEN
The VM32E gene is differently expressed in the distinct cell domains composing the follicular epithelium. Our previous work on the VM32E gene defined the promoter regions required for the control of gene expression in the ventral and dorsal follicle domains. In this report, we present data from a finer dissection of each upstream regulatory region, allowing to draw the functional interactions among different regulatory elements. A 73-bp proximal region (-112/-39) contains regulatory element(s) to dictate the activation of the gene in the follicular epithelium. This region interacts with two other cis-regulatory elements and is absolutely required for their output. The first element (-206/ -113), individually unable to raise reporter expression, elicits gene activity in the ventral domain when joined to the proximal fragment; a second element (-348/-254) joined to the same proximal fragment sustains the full dorsal and ventral activity. Moreover, the ectopic expression driven by some promoter fragments in border or posterior cells uncovers the existence of specific negative regulatory elements. So, the follicular domain specificity of VM32E gene expression is achieved through the combined activities of cell-type specific positive and negative elements.
Asunto(s)
Drosophila/embriología , Drosophila/genética , Regulación del Desarrollo de la Expresión Génica , Oogénesis/fisiología , Secuencias Reguladoras de Ácidos Nucleicos , Membrana Vitelina/fisiología , Animales , Tipificación del Cuerpo , Sondas de ADN , Genes de Insecto , Genes Reporteros , Hibridación in Situ , Modelos Genéticos , Proteínas Recombinantes de Fusión , Transformación Genética , beta-Galactosidasa/metabolismoRESUMEN
The Drosophila vitelline membrane protein gene VM32E is expressed according to a precise temporal and spatial program in the follicle cells. Results from germ line transformation experiments using different fragments of the -465/-39 VM32E region fused to the hsp/lacZ reporter gene revealed that the region -348/-39 is sufficient to confer the wild-type expression pattern. Within this segment, distinct cis-regulatory elements control VM32E expression in ventral and dorsal follicle cells. The region between -135/-113 is essential for expression of the VM32E gene in the ventral columnar follicle cells. Expression in the dorsal domain requires the two regions -348/-254 and -118/-39. Furthermore, the region -253/-119 appears to contain a negative element that represses gene activity in anterior centripetal cells. We suggest that the expression of the VM32E gene throughout the follicular epithelium is controlled by specific cis-regulatory elements acting in distinct spatial domains and following a precise developmental program.