Fig. 1. Sperm-aster microtubules and dynein distribute to the female pronucleus. (A) Fluorescent micrographs of microtubules (MTs) and DNA in bovine zygotes during pronuclear migration and apposition. The male pronucleus (M) occupies a central position throughout these processes, whereas the female pronucleus (F) initially occupies a cortical position (left) and then migrates to the center to meet the male pronucleus (right). During pronuclear migration, sperm-aster microtubules radiate out from a region next to the male pronucleus (asterisk) and extend to the surface of the female pronucleus. The arrow indicates the direction of female pronuclear movement. (B) During pronuclear migration and apposition, dynein intermediate chain concentrates around the female pronucleus (left and center). Dynein also distributes as dim cytoplasmic foci but is absent from the surface of the male pronucleus. Pre-absorption of anti-dynein antibodies with their antigens results in a loss of detection in zygotes (right). Dynein localization is observed in both rhesus-monkey zygotes (B, left) and bovine zygotes (B, center). Scale bars, 10 µm.

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