Oogenesis in Drosophila ovariole

A Drosophila ovariole showing the polar follicle cells and stalks that separate the adjacent cysts. The series of germline cysts (green, BicD) progress through oogenesis as they move posteriorly. The cysts are born at the anterior of the ovariole, and become surrounded by follicle cells (blue - FasIII) as they exit the germarium. Each cyst contains 16 germ cells. One of these is selected to become the oocyte and accumulates higher levels of the BicD protein. BicD is coded by the bicoid gene, and eventually localises to the anterior end of the developing oocyte. FasIII (fasciclin 3) is an adhesion molecule.