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PubMed1991

Drosophila chorion genes: cracking the eggshell's secrets.

The chorion genes of Drosophila are amplified in response to developmental signals in the follicle cells of the ovary prior to their transcription. Their expression is regulated both temporally and spatially within this tissue. They thus serve as models both for the regulation of DNA replication and of developmental transcription. The regulatory elements for DNA amplification have been delineated. Their analysis reveals that amplification is mediated by several regulatory regions and initiates at defined origins within the chorion cluster. Proteins involved in amplification are being identified both by mutations affecting amplification and by DNA binding studies. Regulatory elements for temporal as well as spatial control of chorion gene expression have been characterized, and two candidate transcription factor genes have been cloned.

Animals↗
PubMed1991

Structure and morphogenesis of the eggshell and micropylar apparatus in the olive fly, Dacus oleae (Diptera: Tephritidae).

The egg of the olive fly, Dacus oleae (Diptera, Tephritidae), is laid inside olives and the larva eventually destroys the fruit. The oocyte is surrounded by several distinct layers which are produced during choriogenesis. The chorion covering the main body of the egg outside of the vitelline membrane includes a "wax" layer, an innermost chorionic layer, an endochorion consisting of inner and outer layers separated by pillars and cavities similar to their counterparts in Drosophila melanogaster, as well as inner and outer exochorionic layers. The anterior pole is shaped like an inverted cup, which is chiefly hollow around its base and has very large openings communicating with the environment. Holes through the surface of the endochorion result from deposition of endochorionic substance around follicular cell microvilli. An opening at the apex of the cup provides an entrance for sperm entering the micropylar canal, which traverses the endochorion and continues into a "pocket" in a thickened vitelline protrusion. The micropylar canal is formed by deposition of endochorion and vitelline membrane around an elongated pair of follicular cell extensions. These extensions later degenerate and leave an empty canal about 5 microns in diameter and the narrower pocket about 1 micron in diameter. Respiration is thought to be facilitated by openings at the base of the anterior pole as well as by openings through the "plastron" around the main body of the shell.

Animals↗