Biology subjects

Eichmuller, A.

Publications and source records attributed to Eichmuller, A..

4 recordsLinked to original sources

bioRxiv2022

Ectopic activation of the polar body extrusion pathway triggers cell fragmentation in preimplantation embryos

Cell fragmentation occurs during physiological processes, such as apoptosis, migration, or germ cell development. Fragmentation is also commonly observed during preimplantation development of human embryos and is associated with poor implantation prognosis during Assisted Reproductive Technology (ART) procedures. Despite its biological and clinical relevance, the mechanisms leading to cell fragmentation are unclear. Light sheet microscopy imaging of mouse embryos reveals that compromised spindle anchoring, due to Myo1c knockout or dynein inhibition, leads to fragmentation. We further show that defective spindle anchoring brings DNA in close proximity to the cell cortex, which, in stark contrast to previous reports in mitotic cells, locally triggers actomyosin contractility and pinches off cell fragments. The activation of actomyosin contractility by DNA in preimplantation embryos is reminiscent of the signals mediated by small GTPases throughout polar body extrusion (PBE) during meiosis. By interfering with the signals driving PBE, we find that this meiotic signaling pathway remains active during cleavage stages and is both required and sufficient to trigger fragmentation. Together, we find that fragmentation happens in mitosis after ectopic activation of actomyosin contractility by signals emanating from DNA, similar to those observed during meiosis. Our study uncovers the mechanisms underlying fragmentation in preimplantation embryos and, more generally, offers insight into the regulation of mitosis during the maternal-zygotic transition.

developmental biology↗

bioRxiv2022

The filipodia-like protrusions of adjacent somatic cells shape the developmental potential of mouse oocytes

The oocyte must grow and mature before fertilization, thanks to a close dialogue with the somatic cells which surround it. Part of this communication is through filopodialike protrusions, called transzonal projections (TZPs), sent by the somatic cells to the oocyte membrane. To investigate the contribution of TZPs to oocyte quality, we impaired their structure by generating a full knockout mouse of the TZP structural component Myosin-X (MYO10). Using spinning disk and super-resolution microscopy combined with a machine learning approach to phenotype oocyte morphology, we show that the lack of Myo10 decreases TZP density during oocyte growth. Reduction in TZPs does not prevent oocyte growth but impairs oocyte-matrix integrity. Importantly, we reveal by transcriptomic analysis that gene expression is altered in TZP-deprived oocytes, and that oocyte maturation and subsequent early embryonic development are partially affected, effectively reducing mouse fertility. We propose that TZPs play a role in the structural integrity of the germline-somatic complex, which is essential for regulating gene expression in the oocyte and thus its developmental potential.

cell biology↗

bioRxiv2022

An interpretable and versatile machine learning approach for oocyte phenotyping

Meiotic maturation is a crucial step of oocyte development allowing its potential fertilization and embryo development. Elucidating this process is important both for fundamental research and assisted reproductive technology. However, only few computational tools, based on non-invasive measurements, are currently available to characterize oocyte meiotic maturation. Here, we develop a computational framework to phenotype oocytes based on images or movies acquired exclusively in transmitted light. We first trained neural networks to segment the contours of oocytes and their zona pellucida using a diverse cohort of both mouse and human oocytes. We then defined a comprehensive set of morphological features to describe a single oocyte. We have implemented these steps in a versatile and user-friendly open source Fiji plugin available to the mouse and human oocyte community. Then, we present a machine learning pipeline based on selected features to automatically recognize oocyte populations and determine their morphological differences. Its first application is a novel approach to screen oocyte strains and automatically identify their morphological characteristics. We demonstrate its potential by phenotyping a well characterized genetically modified mouse oocyte strain. Its second application is to predict and characterize the maturation potential of oocytes. Importantly, we identify two new features to assess mouse oocyte maturation potential, consisting in the texture of the zona pellucida and the cytoplasmic particles size. Eventually, we tested whether these mouse oocyte quality features were applicable to human oocytes developmental potential.

bioinformatics↗

bioRxiv2021

Cytoplasmic forces functionally reorganize nuclear condensates in oocytes

Cells remodel their cytoplasm with force-generating cytoskeletal motors1. Their activity generates random forces that stir the cytoplasm, agitating and displacing membrane-bound organelles like the nucleus in somatic2-4 and germ5-7 cells. These forces are transmitted inside the nucleus4,7, yet their consequences on liquid-like biomolecular condensates8-10 residing in the nucleus remain unexplored. Here, we probe experimentally and computationally diverse nuclear condensates, that include nuclear speckles, Cajal bodies, and nucleoli, during cytoplasmic remodeling of female germ cells named oocytes. We discover that growing mammalian oocytes deploy cytoplasmic forces to timely impose multiscale reorganization of nuclear condensates for the success of meiotic divisions. These cytoplasmic forces accelerate nuclear condensate collision-coalescence and molecular kinetics within condensates. Inversely, disrupting the forces decelerates nuclear condensate reorganization on both scales, compromising condensate-associated mRNA processing and consequently hindering oocyte divisions that drive female fertility. We establish that cytoplasmic forces can reorganize nuclear condensates in an evolutionary conserved fashion in insects. Our work implies that cells evolved a mechanism, based on cytoplasmic force tuning, to functionally regulate a broad range of nuclear condensates across scales. This finding opens new perspectives when studying condensate-associated pathologies like cancer, neurodegeneration and viral infections11-13.

cell biology↗