Microinjection and Transgenesis. Springer Lab Manual

The early Drosophila embryos are particularly well suited for microinjection purposes for three major reasons. Firstly, they are easy to collect. Well-fed, healthy females can lay between two and three eggs per hour. Therefore, the yield from a single bottle containing between one and two 100 females can exceed 200 eggs every 30 min. Secondly, they are easy to handle and prepare for microinjection. The eggs of Drosophila are shaped like an ellipsoid whose major and minor axis are about 420 and 150 µm and have a volume of around 10 nl. This relatively large size facilitates their handling and microinjection without the need for highly sophisticated and expensive setups. Surrounding the cell membrane there is a thin, stiff, vitelline membrane which is covered by a rigid proteinaceus chorion. The chorion is too hard to allow for the penetration of the fine needles required for microinjection, but it can easily be removed by mechanical methods or chemical treatment. Finally, the suitability of the Drosophila embryo for microinjection is due to the special characteristics of early embryogenesis in Drosophila. After fertilization and fusion of the male and female pronuclei, nuclear proliferation proceeds through a rapid series of synchronous mitotic divisions which occur without partitioning the nuclei by cell membranes. These nuclear cycles lack the G1 and G2 phases and are sustained and regulated by maternal products