Germ cell nests and germline cysts

Germ cells in many organisms develop in clusters called germline cysts. These structures have been well described in the Drosophila model system where the cystoblast divides several times without completing cytokinesis to form the cysts. Similar structures are found in a variety of animals including mammals. In the mouse, germ cell cysts form from the mitotic division of primordial germ cells. The cysts fragment and associate in nests with fragments from other cysts. Eventually the nests break apart and individual oocytes are surrounded by pregranulosa cells forming primordial follicles. The mechanisms controlling nest breakdown are beginning to be elucidated in the mouse. While it is clear in Drosophila that germ cell cysts serve an important function in nourishing the oocyte, functions in other species are not clear though a wide variety of roles has been proposed.