The chorion genes of the medfly. II. DNA sequence evolution of the autosomal chorion genes s18, s15, s19 and s16 in Diptera

Patterns of inner chorion structure in Anastrepha (Diptera: Tephritidae) eggs

The inner chorion structure of Anastrepha eggs from 16 species of various infrageneric taxonomic groups is described by scanning and transmission electron microscopy. The layers of the chorion, the outer egg membrane, are structurally similar. Furthermore, an additional trabecular layer (ATL) that exists in some species, together with other characteristics, facilitates the recognition of four patterns of chorion structuring: Pattern I, in which the ATL layer is absent, is found in Anastrepha amita, the Anastrepha fraterculus complex, Anastrepha obliqua, Anastrepha sororcula, Anastrepha suspensa and Anastrepha zenildae (fraterculus group), and Anastrepha bistrigata and Anastrepha striata (striata group); Pattern II in Anastrepha serpentina (serpentina group), Anastrepha grandis (grandis group) and Anastrepha pseudoparallela (pseudoparallela group), in which the ATL presents large open spaces with pillars; Pattern III, found in Anastrepha consobrina (pseudoparallela group), in which the ATL is composed of round cavities; and Pattern IV, found in Anastrepha alveata and Anastrepha pickeli (spatulata group), where the large ATL cavities are reticulated. Comparatively, the chorion structure in Anastrepha eggs is more complex than in eggs of other fruit flies, e.g., Bactrocera, Rhagoletis and Ceratitis.

Proteomics reveals novel components of the Anopheles gambiae eggshell

While genome and transcriptome sequencing has revealed a large number and diversity of Anopheles gambiae predicted proteins, identifying their functions and biosynthetic pathways remains challenging. Applied mass spectrometry-based proteomics in conjunction with mosquito genome and transcriptome databases were used to identify 44 proteins as putative components of the eggshell. Among the identified molecules are two vitelline membrane proteins and a group of seven putative chorion proteins. Enzymes with peroxidase, laccase and phenoloxidase activities, likely involved in cross-linking reactions that stabilize the eggshell structure, also were identified. Seven odorant binding proteins were found in association with the mosquito eggshell, although their role has yet to be demonstrated. This analysis fills a considerable gap of knowledge about proteins that build the eggshell of anopheline mosquitoes.

Conservation of epigenetic regulation, ORC binding and developmental timing of DNA replication origins in the genus Drosophila

There is much interest in how DNA replication origins are regulated so that the genome is completely duplicated each cell division cycle and in how the division of cells is spatially and temporally integrated with development. In the Drosophila melanogaster ovary, the cell cycle of somatic follicle cells is modified at precise times in oogenesis. Follicle cells first proliferate via a canonical mitotic division cycle and then enter an endocycle, resulting in their polyploidization. They subsequently enter a specialized amplification phase during which only a few, select origins repeatedly initiate DNA replication, resulting in gene copy number increases at several loci important for eggshell synthesis. Here we investigate the importance of these modified cell cycles for oogenesis by determining whether they have been conserved in evolution. We find that their developmental timing has been strictly conserved among Drosophila species that have been separate for approximately 40 million years of evolution and provide evidence that additional gene loci may be amplified in some species. Further, we find that the acetylation of nucleosomes and Orc2 protein binding at active amplification origins is conserved. Conservation of DNA subsequences within amplification origins from the 12 recently sequenced Drosophila species genomes implicates members of a Myb protein complex in recruiting acetylases to the origin. Our findings suggest that conserved developmental mechanisms integrate egg chamber morphogenesis with cell cycle modifications and the epigenetic regulation of origins.

Genomic organization and functional characterization of the alcohol dehydrogenase locus of Ceratitis capitata (Medfly)

Approximately 30 kb of genomic DNA enclosing the Adh locus from the medfly, Ceratitis capitata have been cloned and about 15 kb has been structurally and functionally characterized. The locus consists of two genes, Adh-1 and Adh-2, separated by an intergenic region, which is polymorphic in size ranging from approximately 6.4 kb to 8.1 kb. Both genes consist of three exons and two introns. The introns are below 200 bp in size, except the 1st intron of Adh-1, which is unexpectedly long, variable in size and contains a deleted mariner-like element (postdoc). The two genes are transcribed in different orientations. The Adh-2 gene shows the typical pattern of transcription seen in the homologous genes of Drosophilidae presenting high levels of expression in the fat body, gut and ovaries. The Adh-1 gene is only expressed in the body muscle tissues of embryos, larvae and adult flies, raising the question of what its biological function may be. A DNA fragment containing bases -102 to -1666 relative to the first base of the initiating ATG of Adh-1 is sufficient to drive the expression of a reporter gene in body muscles of Drosophila melanogaster embryos, larvae and adult flies. The study provides further insights into the evolution of the Adh genes of higher diptera.

A novel role for the Bombyx Slbo homologue, BmC/EBP, in insect choriogenesis

One previously unidentified cDNA clone coding for a C/EBP factor, BmC/EBP, was isolated from Bombyx mori follicular cells. This is the first time that a C/EBP factor has been isolated and characterized in Lepidoptera. We provide information concerning structural features and developmental specificity, as well as in vitro interaction properties with chorion gene promoter modules. BmC/EBP was capable of effectively recognizing homologous binding sites from chorion gene promoters derived from flies and other moths, despite significant diversity of chorion structure, gene organization, and gene expression profiles. We propose that the relative concentration of BmC/EBP, in relation to its differential binding affinity for promoter cis-elements, results in activation or repression of silkmoth chorion gene expression.

Medfly promoters relevant to the sterile insect technique

This review summarizes structural and functional studies on medfly promoters and regulatory elements that can be used for driving sex-specific, conditional and constitutive gene expression in this species. Sex-specific and conditional promoters are important for generating transgenic sexing strains that could increase the performance of the Sterile Insect Technique while strong constitutive promoters are necessary for developing sensitive transgenic marker systems. The review focuses on the functional analysis of the promoters of two male-specific and heat shock medfly genes. A special emphasis is put on the potential utility of these promoters for developing transgenic sexing strains.