Production of functional gametes is important for all multicellular organisms with sexual reproduction. Although oogenesis substantially differs among species, several features are common even for evolutionary distant species. In a wide variety of organisms, gametes develop within clusters of germ line cells called cysts. Cyst cells interconnected by ring canals display synchronous mitoses in all species. Another gametogenesis feature shared by various species is the formation of a follicle as a specialized compartment for the growth and development of germline cells. In fruit fly, as well as in many other species, oocyte growth and development are provided with substances produced in nurse cells during all stages of oogenesis. There are two different types of direct transport, selected and nonselected, that are used to deliver material from nurse cells to oocyte. Slow and highly selective transport takes place during early development of the egg chamber, and it is essential for oocyte determination and polarity. Selective transport initially based on a special branched structure, called fusome which connected all cyst cells together. The fusome is involved in organizing and structuring the microtubule network in Drosophila follicle and acquisition of a single microtubule organizing center in the oocyte. Microtubule-dependent targeted transport of certain mRNAs, proteins and organelles from nurse cells into the oocytes result in the establishment of proper polarity within the oocyte marked by the asymmetric distribution of Bic-D, Egl, Orb, and Par-1 proteins. Nonselective transport or dumping of the nurse cell cytoplasm into the oocyte starts after stage 10 of egg chamber development. In this period the most of the nurse cells contents is rapidly transferred into the oocyte. Dumping ends with the formation of mature egg, ready for fertilization. It was shown that dumping is actin filament dependent. Two distinct actin filament networks are important for dumping: subcortical actin filament system which is required for nurse cell contraction along with cytoplasmic myosin and a network of cytoplasmic actin filaments extents from the nurse cell surface to the nuclei. Another factor that alters dumping is a structural defect in ring canals. Dumping can as well be frustrated by the irregular migration of the follicular cell group that migrates centripetally between the nurse cells and the oocyte, enclosing the anterior of the egg. Heat stress is also a dumping-distorting factor that leads to dumpless phenotype.
|Title of host publication||Ovarian Cysts|
|Subtitle of host publication||Symptoms, Causes and Treatment|
|Publisher||Nova Science Publishers, Inc.|
|Number of pages||17|
|Publication status||Published - 2010|