On the chromatin of the immature oocyte : from morphology to function and regulatory mechanisms mediated by follicular cells

In her comment entitled ‘Nuclear histochemistry: its history in fifty volumes’ (Eur J Histochem 2006; 50:79-81) Maria Gabriella Manfredi Romanini referred to “nuclear histochemistry” as a “real molecular biology in situ, applied to research on dynamic processes in the nucleus, which makes the microscopic and histo- chemical approach absolutely irreplaceable for the progress of our understanding of cell biology”. These words perfectly exemplify the research path that is elucidating the process of remodeling of chromatin configuration within the nucleus of the mammalian oocyte. This process, which occurs towards the end of the oocyte differentiation phase before meiotic resumption, has received much attention in the last decade since it has a tremendous impact on the capability of the oocyte to generate an embryo after fertilization. The study of the oocyte chromatin by means of classical morphological and histochemical approaches has given a fundamental contribution to our understanding of oocyte biology and has paved the way to functional and mechanistic studies. Several research groups worldwide, including ours, are indeed dedicating a large amount of studies to find the relationship between morphological and functional aspects of the oocyte chromatin remodeling process, to reveal the molecular mechanisms involved, as well as to clarify the contribution of the follicular compartment. Here, we summarize some studies intended to give insight into the mechanism(s) regulating this complex process, including recent findings indicating that ovarian granulosa cells and their coupling with the oocyte through gap junctions are implicated in such a process.