PT  - JOURNAL ARTICLE
AU  - Schneider, Isabell
AU  - de Ruijter-Villani, Marta
AU  - Hossain, M. Julius
AU  - Stout, Tom A. E.
AU  - Ellenberg, Jan
TI  - Non-rodent mammalian zygotes assemble dual spindles despite the presence of paternal centrosomes
AID  - 10.1101/2020.10.16.342154
DP  - 2020 Jan 01
TA  - bioRxiv
PG  - 2020.10.16.342154
4099  - http://biorxiv.org/content/early/2020/10/16/2020.10.16.342154.short
4100  - http://biorxiv.org/content/early/2020/10/16/2020.10.16.342154.full
AB  - The first mitosis of the mammalian embryo must partition the parental genomes contained in two pronuclei. In rodent zygotes, sperm centrosomes are degraded and, instead, acentriolar microtubule organizing centers and microtubule self-organization guide the assembly of two separate spindles around the genomes. In non-rodent mammals, including human or bovine, centrosomes are inherited from the sperm and have been widely assumed to be active. Whether non-rodent zygotes assemble a single centrosomal spindle around both genomes, or follow the dual spindle self-assembly pathway is unclear. To address this, we investigated spindle assembly in bovine zygotes by systematic immunofluorescence and real-time light-sheet microscopy. We show that two independent spindles form around the parental genomes despite the presence of centrosomes, which had little effect on spindle structure and were only loosely connected to the two spindles. We conclude that the dual spindle assembly pathway is conserved in non-rodent mammals. This could explain whole parental genome loss frequently observed in blastomeres of human IVF embryos.Summary This study investigates spindle assembly during the first embryonic division in bovine zygotes that, like human, inherit centrosomes from the sperm. It shows that two independent microtubule arrays form by self-organization around parental genomes with only loosely connected centrosomes.Competing Interest StatementJan Ellenberg is scientific co-founder and advisor of Luxendo GmbH (part of Bruker), which makes light-sheet based microscopes commercially available.AbbreviationsAUCarea under the curveIFimmunofluorescenceIVFin vitro fertilizationFWHMfull width half maximumMTOCmicrotubule organizing centerNEBDnuclear envelope break downPN/spronucleus/pronuclei