Non-rodent mammalian zygotes assemble dual spindles despite the presence of paternal centrosomes
This study investigates spindle assembly during the first embryonic division in bovine zygotes that, like human, inherit centrosomes from the sperm. Combining systematic immunofluorescence and real-time light sheet microscopy we show that chromosomal nucleation and microtubule self-organization drive the formation of two independent spindles around the parental genomes. Surprisingly, the centrosomes had little effect on spindle structure and were only loosely connected to them. We conclude that the mechanism of zygotic dual spindle assembly is conserved in non-rodent mammals.