live cell imaging and analysis of nuclear dynamics in mouse oocytes

Impact of Cytoskeleton on Nuclear Shape and Condensate Dynamics in Mouse Oocytes

Nuclear positioning is essential for multiple cellular and developmental functions1,2,3,4,5. Mammalian female germ cells named oocytes remodel their cytoplasm to position the nucleus at the cell center despite undergoing an asymmetric division in size, which relies on subsequent chromosome off-centering6 (Figure 1). This centering of the nucleus predicts successful oocyte development in mice and humans7, 8, and thus, their embryogenic potential (Figure 1).
Cytoplasmic remodeling in mouse oocytes is driven primarily by the actomyosin cytoskeleton9 (Figure 2). Its activity generates mechanical forces that agitate, reposition, and penetrate the nucleus10 (Figure 2). Consequently, this cytoplasmic-to-nucleoplasmic force transmission tunes the dynamics of nuclear messenger RNA-processing organelles named nuclear speckles11, one of several membrane-less organelles in the nucleus known as biomolecular condensates12,13,14,15,16 (Figure 2).
Live imaging has been decisive in deciphering the functional implications of nuclear agitation. Movies of nuclear migration over hours, as well as high-temporal resolution movies of the actin mesh and the bulk cytoplasm, largely contributed to the elaboration of a theoretical model for nuclear positioning, linking different timescales9. Also, high temporal resolution movies of the cytoplasm, nuclear outline and nuclear components such as chromatin and nuclear condensates, highlighted the role of cytoskeleton-based agitation of the nucleus on RNA-processing and gene expression in mouse oocytes, bridging different spatiotemporal scales within the cell10,11. Altogether, such a scale-crossing approach based on live imaging provided the first rationale linking cytoskeletal agitation of the nucleus to the developmental success of oocytes.
The protocol provides the imaging and image analysis pipeline used to study the transmission of cytoplasmic forces (generated primarily by F-actin and partly by microtubules) to the nucleus and its internal components in mouse oocytes. The outcome of these experiments is to capture the continuum of forces across spatial scales, from the cytoskeleton in the cytoplasm to the nuclear interior via high temporal resolution movies as shown in two recent studies10,11, that established the link between cytoplasmic active movements, fluctuations of the nuclear outline, as well as movement and surface fluctuations of a single type of nuclear biomolecular condensates: nuclear speckles. The same approach may be applied to other model systems where cytoplasmic forces are expected to change, such as in the context of malignant cancer cells17.

Author Spotlight: Elucidating the Dynamics of Mechano-Transduction and Nuclear Agitation in Mouse Oocytes

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

The lab aims to better understand the mechanisms involved in the acquisition of female gamut quantity, which is essential for the reproduction of sexual species using the mouse oocytes model system. Recently, we identified a novel mechanical transduction process that promotes agitation of the nucleus and its content, leading to the fine regulation of maternal RNAs in mouse oocytes. The imaging and image analysis pipeline presented in this protocol allows us to highlight the transmission of cytoskeletal forces as a continuum across scales from the cytoplasm to the nucleus and its components, including nuclear RNA processing bodies in mouse oocytes.This protocol provides simple tools that allow us to address first transmission across multiple cellular scales in a single pipeline for the first time. Complemented with biophysical modeling, this protocol constitutes a non-invasive technique to address changes in nuclear mechanics and the dissipation of energy across cellular compartments.

Live Cell Imaging and Analysis of Nuclear Dynamics in Mouse Oocytes

live-cell-imaging-and-analysis-of-nuclear-dynamics-in-mouse-oocytes

Research

JoVE Journal

Biology

50 Views.  Collège de France, CNRS, INSERM, Université PSL. Live Cell Imaging and Analysis of Nuclear Dynamics in Mouse Oocytes