capturing-cytoskeleton-based-agitation-mouse-oocyte-nucleus-across

Capturing Cytoskeleton-Based Agitation of the Mouse Oocyte Nucleus Across Spatial Scales

A major challenge in understanding the causes of female infertility is to elucidate mechanisms governing the development of female germ cells, named ...

Collège de France, CNRS, INSERM, Université PSL

The position of the nucleus in a cell can instruct morphogenesis in some cases, conveying spatial and temporal information and abnormal nuclear positioning can lead to disease. In oocytes from worm, sea urchin, frog and some fish, nucleus position regulates embryo development, it marks the animal pole and in Drosophila it defines the future dorso-ventral axis of the embryo and of the adult body plan. However, in mammals, the oocyte nucleus is centrally located and does not instruct any future embryo axis. Yet an off-center nucleus correlates with poor outcome for mouse and human oocyte development. This is surprising since oocytes further undergo two extremely asymmetric divisions in terms of the size of the daughter cells (enabling polar body extrusion), requiring an off-centering of their chromosomes. In this review we address not only the bio-physical mechanism controlling nucleus positioning via an actin-mediated pressure gradient, but we also speculate on potential biological relevance of nuclear positioning in mammalian oocytes and early embryos.

Control of nucleus positioning in mouse oocytes.

Development of fluorescence distribution assays like FRAP (fluorescence recovery after photobleaching) or photoactivation has had a great impact in studying intracellular protein dynamics. In particular, the cytoskeleton field largely benefited from these techniques, with lots of new information provided about the dynamics and organization of actin networks whithin cells.In mouse oocyte, actin photoactivation has been very useful to determine the dynamics of different actin structures involved in meiotic divisions, including a cytoplasmic meshwork and a subcortical actin layer.Here, we describe a method, actin photoactivation, to determine the dynamics of the actin cytoplasmic meshwork and the subcortical actin layer during the first meiotic division in the mouse oocyte, that could be adapted to other actin structures or other stages of meiotic divisions.

Photoactivation of Actin in Mouse Oocyte.

Cells are the building units of living organisms and consequently adapt to their environment by modulating their intracellular architecture, in particular the position of their nucleus. Important efforts have been made to decipher the molecular mechanisms involved in nuclear positioning. The LINC complex at the nuclear envelope is a very important part of the molecular connectivity between the cell outside and the intranuclear compartment, and thus emerged as a central player in nuclear mechanotransduction. More recent concepts in nuclear mechanotransduction came from studies involving nuclear confined migration, compression or swelling. Also, the effect of nuclear mechanosensitive properties in driving cell differentiation raises the question of nuclear mechanotransduction and gene expression and recent efforts have been done to tackle it, even though it remains difficult to address in a direct manner. Eventually, an original mechanism of nucleus positioning, mechanotransduction and regulation of gene expression in the non-adherent, non-polarized mouse oocyte, highlights the fact that nuclear positioning is an important developmental issue.

Nuclear positioning as an integrator of cell fate.

Preserving maternal RNA transmitted by the oocyte to its progeny is an essential aspect of oogenesis, yet not much is known about how this is achieved in mammalian species. In a recent issue of Science, Cheng et al. uncover a novel structure involved in this fundamental aspect.

Article	Year
Control of nucleus positioning in mouse oocytes. Seminars in cell & developmental biology\| PubMed ID: 28807882	2018
Photoactivation of Actin in Mouse Oocyte. Methods in molecular biology (Clifton, N.J.)\| PubMed ID: 29961263	2018
Nuclear positioning as an integrator of cell fate. Current opinion in cell biology\| PubMed ID: 30594054	2019
A mitochondrial niche protects oocyte RNPs. Developmental cell\| PubMed ID: 36473456	2022

Maria Almonacid

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