Myosin VI is an unconventional Myosin that has been implicated in vesicle transport and membrane trafficking. We isolated lethal mutants of Myosin VI, which lack protein once maternal supplies have been utilised during embryogenesis. Dorsal closure, where there is a ring of Myosin VI at the edge of the migrating epithelial sheet, is often abnormal. The sheet of migrating cells is irregular, rather than a smooth epithelium and cells begin to detach. Some embryos hatch into larvae, containing detached cells loose in the haemolymph. Myosin VI is crucial for correct cell morphology and maintenance of adhesive cellular contacts within epithelial cell layers.

extramacrochaetae (emc) functions during many developmental processes in Drosophila, such as sensory organ formation, sex determination, wing vein differentiation, regulation of eye photoreceptor differentiation, cell proliferation and development of the Malpighian tubules, trachea and muscles in the embryo. It encodes a Helix-Loop-Helix transcription factor that negatively regulates bHLH proteins. We show here that emc mRNA and protein are present throughout oogenesis in a dynamic expression pattern and that emc is involved in the regulation of chorionic appendage formation during late oogenesis. Expression of sense and antisense emc constructs as well as emc follicle cell clones leads to eggs with shorter, thicker dorsal appendages that are closer together at base than in the wild type. We demonstrate that emc lies downstream of fs(1)K10, gurken and EGFR in the Grk/EGFR signalling pathway and that it participates in controlling Broad-Complex expression at late stages of oogenesis.

We have isolated and sequenced a cDNA encoding a predicted 524 amino acid protein from a Drosophila melanogaster ovarian library. Sequence comparisons suggest that this protein encodes a sodium-dependent inorganic phosphate co-transporter similar to a sequence isolated from a rat brain library. In situ hybridisation to messenger RNA in ovaries shows strong expression in germarium at stage 2 of oogenesis. Expression is then weak in follicle cells until stage 10, when high transcript levels are seen in the nurse cells and transferred to the oocyte. This presumably reflects functions in oogenesis and the production of stored mRNAs for use in embryogenesis.

We report that Drosophila unconventional myosin VI, encoded by Myosin heavy chain at 95F (Mhc95F), is required for both imaginal disc and egg chamber morphogenesis. During oogenesis, Mhc95F is expressed in migrating follicle cells, including the border cells, which migrate between the nurse cells to lie at the anterior of the oocyte; the columnar cells that migrate over the oocyte; the centripetal cells that migrate between the oocyte and nurse cells; and the dorsal-anterior follicle cells, which migrate to secrete the chorionic appendages. Its function during development has been studied using a targeted gene silencing technique, combining the Gal4-UAS targeted expression system and the antisense RNA technique. Antibody staining shows that the expression of myosin 95F is greatly decreased in follicle cells when antisense Mhc95F RNA is expressed. Interfering with expression of Drosophila myosin VI at various developmental stages frequently results in lethality. During metamorphosis it results in adult flies with malformed legs and wings, indicating that myosin VI is essential for imaginal disc morphogenesis. During oogenesis, abnormal follicle cell shapes and aberrant follicle cell migrations are observed when antisense Mhc95F is expressed in follicle cells during stages 9 to 10, suggesting that the Drosophila myosin VI is required for follicle cell epithelial morphogenesis.