The role of BicD, Egl, Orb and the microtubules in the restriction of meiosis to the Drosophila oocyte

The oocyte is the only cell in Drosophila that goes through meiosis with me iotic recombination, hut several germ cells in a 16-cell cyst enter meiosis and form synaptonemal complexes (SC) before one cell is selected to become the oocyte, Using an antibody that recognises a component of the SC or the synapsed chromosomes, we have analysed how meiosis becomes restricted to o ne cell, in relation to the other events in oocyte determination. Although BicD and egl mutants both cause the development of cysts with no oocyte, th ey have opposite effects on the behaviour of the SC: none of the cells in t he cyst form SC in BicD null mutants, whereas all of the cells do in egl an d orb mutants. Furthermore, unlike all cytoplasmic markers for the oocyte, the SC still becomes restricted to one cell when the microtubules are depol ymerised, even though the BicD/Egl complex is not localised, These results lead us to propose a model in which BicD, Egl acid Orb control entry into m eiosis by regulating translation.