Acentriolar microtubule organizing centers regulate spindle positioning in the mouse zygote
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[EMBARGOED UNTIL 12/01/2027] Asymmetrical division leading to uneven blastomere size during early embryo development is associated with decreased implantation and pregnancy rates in humans. Given that the spindle position within the cell dictates the cleavage plane, the success of symmetrical division after fertilization depends on its location at the center of the cell. The formation and positioning of the spindle depend on microtubule filaments, a major cytoskeletal component of the cell. In mice, the zygote lacks centrosomes but contains acentriolar microtubule-organizing centers (MTOCs) that form the poles of the first mitotic spindle. Thus far, the biological significance of MTOCs in spindle positioning remains unexplored. We used a transgenic mouse model expressing Cep192-eGFP to visualize MTOCs in live one-cell embryos and depleted MTOCs via multiphoton laser ablation to understand the functional role of MTOCs. We demonstrate that the localization of MTOCs to pronuclei is dependent on microtubules and F-actin. We also find that MTOCs regulate spindle positioning in zygotes, a previously unknown phenomenon. These findings help to understand the factors that regulate spindle positioning in early mammalian embryos, ensuring the faithful placement of the cleavage plane and highly symmetrical division.
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M.S.