Biology subjects

Pelzer, D.

Publications and source records attributed to Pelzer, D..

4 recordsLinked to original sources

bioRxiv2023

Inverse blebs operate as hydraulic pumps during mouse blastocyst formation

During preimplantation development, mouse embryos form a fluid-filled lumen, which sets their first axis of symmetry1,2. Pressurized fluid breaks open cell-cell contacts and accumulates into pockets, which gradually coarsen into a single lumen3-5. During coarsening, the adhesive and contractile properties of cells are thought to guide intercellular fluid (IF) but what cell behavior may control fluid movements is unknown. Here, we report large fluid-filled spherical membrane intrusions called inverse blebs6,7 growing into cells at adhesive contacts. At the onset of lumen coarsening, we observed hundreds of inverse blebs throughout the embryo, each dynamically filling with IF and retracting within a minute. We find that inverse blebs grow due to pressure build-up resulting from luminal fluid accumulation and cell-cell adhesion, which locally confines fluid. Inverse blebs then retract due to actomyosin contraction, which effectively redistributes fluid within the intercellular space. Importantly, inverse blebs show topological specificity and only occur at contacts between two cells, not at contacts formed by multiple cells, which essentially serve as fluid sinks. Manipulating the topology of the embryo reveals that, in the absence of sinks, inverse blebs pump fluid into one another in a futile cycle. We propose that inverse blebs operate as hydraulic pumps to promote luminal coarsening, thereby constituting an instrument used by cells to control fluid movement.

developmental biology↗

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↗

bioRxiv2020

Multiscale analysis of single and double maternal-zygotic Myh9 and Myh10 mutants during mouse preimplantation development

During the first days of mammalian development, the embryo forms the blastocyst, the structure responsible for implanting the mammalian embryo. Consisting of an epithelium enveloping the pluripotent inner cell mass and a fluid-filled lumen, the blastocyst results from a series of cleavages divisions, morphogenetic movements and lineage specification. Recent studies identified the essential role of actomyosin contractility in driving the morphogenesis, fate specification and cytokinesis leading to the formation of the blastocyst. However, the preimplantation development of contractility mutants has not been characterized. Here, we generated single and double maternal-zygotic mutants of non-muscle myosin-II heavy chains (NMHC) to characterize them using multiscale imaging. We find that Myh9 (NMHC II-A) is the major NMHC during preimplantation development as its maternal-zygotic loss causes failed cytokinesis, increased duration of the cell cycle, weaker embryo compaction and reduced differentiation, whereas Myh10 (NMHC II-B) maternal-zygotic loss is much less severe. Double maternal-zygotic mutants for Myh9 and Myh10 show a much stronger phenotype, failing most attempts of cytokinesis. We find that morphogenesis and fate specification are affected but nevertheless carry on in a timely fashion, regardless of the impact of the mutations on cell number. Strikingly, even when all cell divisions fail, the resulting single-celled embryo can initiate trophectoderm differentiation and lumen formation by accumulating fluid in increasingly large vacuoles. Therefore, contractility mutants reveal that fluid accumulation is a cell-autonomous process and that the preimplantation program carries on independently of successful cell division.

developmental biology↗

bioRxiv2020

Foxm1 regulates neuronal progenitor fate during spinal cord regeneration

Mammals have limited tissue regeneration capabilities, particularly in the case of the central nervous system. Spinal cord injuries are often irreversible and lead to the loss of motor and sensory function below the site of the damage [1]. In contrast, amphibians such as Xenopus tadpoles can regenerate a fully functional tail, including their spinal cord, following amputation [2,3]. A hallmark of spinal cord regeneration is the re-activation of Sox2/3+ progenitor cells to promote regrowth of the spinal cord and the generation of new neurons [4,5]. In axolotls, this increase in proliferation is tightly regulated as progenitors switch from a neurogenic to a proliferative division via the planar polarity pathway (PCP) [6-8]. How the balance between self-renewal and differentiation is controlled during regeneration is not well understood. Here, we took an unbiased approach to identify regulators of the cell cycle expressed specifically in X.tropicalis spinal cord after tail amputation by RNAseq. This led to the identification of Foxm1 as a potential key transcription factor for spinal cord regeneration. Foxm1-/- X.tropicalis tadpoles develop normally but cannot regenerate their spinal cords. Using single cell RNAseq and immunolabelling, we show that foxm1+ cells in the regenerating spinal cord undergo a transient but dramatic change in the relative length of the different phases of the cell cycle, suggesting a change in their ability to differentiate. Indeed, we show that Foxm1 does not regulate the rate of progenitor proliferation but is required for neuronal differentiation leading to successful spinal cord regeneration.

developmental biology↗