Changes of Large-Scale Chromatin Configuration During Mammalian Oocyte Differentiation

Mammalian oocyte development is characterized by impressive dynamic changes in chromatin structure and function within the germinal vesicle (GV). During meiotic arrest at diplotene stage, and particularly during the oocyte growth phase leading to the formation of the fully-grown and dif- ferentiated oocyte, the chromatin enclosed within the GV is subjected to several levels of regulation controlling both its structure and function. Morphologically, the chromosomes lose their individuality and form a loose chromatin mass, which in turn undergoes profound and dynamic rearrangements within the GV before the meiotic resumption. These large- scale chromatin configuration changes have been studied in several mam- mals and progressive condensation of the chromatin has been related to the achievement of meiotic and developmental potential. In this chapter we will give an overview of the scientific literature on this topic, highlight- ing how changes in chromatin configurations are related to both functional and structural modifications occurring in the oocyte nuclear and cytoplas- mic compartments. Further, we will discuss the machinery regulating this complex process, including the fundamental role exerted by the follicular cells also throughout intracellular messenger dependent mechanism(s). Finally, we will discuss possible implications for the field of assisted reproductive technologies.