Abstract
Understanding the mechanism of nucleus positioning and the information conveyed by it constitute important research axes in Developmental and Reproductive Biology. In most species, the position of the oocyte nucleus predefines the axes of the future embryo. In the mouse oocyte, the nucleus is centered by a pressure gradient generated by a cytoplasmic actin meshwork nucleated by Formin 2. The discovery of this centering mechanism allowed to better understanding its biological significance. Centering the nucleus in mouse oocytes involves a novel mechano-transduction process, which promotes agitation of the nucleus and of its content, including chromatin, thereby modulating gene expression. This fine regulation of the maternal RNA stores explains why nucleus centering is predictive of the quality of the female gamete and of its developmental potential after fertilization.
Highlights
Understanding the mechanisms which regulate nucleus positioning and deciphering which information this positioning conveys constitutes a major research axis in Reproductive as well as in Developmental biology
These results argue in favor of an entirely new mechanism of gene regulation by mechano-transduction, driven by the dynamics of the cytoplasmic actin network impacting chromatin and gene expression inside the nucleus through fluctuations of the nuclear envelope
The same physical phenomenon that centers the oocyte nucleus generates a unique type of mechanotransduction process in which the dynamics of the actin network in the cytoplasm agitates the nucleus by actively “massaging” its surface
Summary
Understanding the mechanisms which regulate nucleus positioning and deciphering which information this positioning conveys constitutes a major research axis in Reproductive as well as in Developmental biology. In nematode, sea urchin, Xenopus and zebrafish, the oocyte nucleus marks the animal pole, which will instruct future embryo axes, and in Drosophila, it defines the future dorso-ventral axis of the embryo. This is not the case in mammals where the nucleus is found perfectly centered at the end of oocyte growth in the ovary. The work of Maria Almonacid, under the supervision of Marie-Hélène Verlhac at the CIRB, Collège de France, sought to better understand this unexpected link between centering of the nucleus and successful meiosis in the mammalian oocyte [3]
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