FIG. 1.

Localization of ORC2 and MCM7 in the zygote 1–2 h after fertilization. MII oocytes or zygotes shortly after fertilization were fixed and double immunostained with antibodies to ORC2 (green, b and f) and MCM7 (red, c and g), and counterstained with DAPI (a and e), then visualized by confocal microscopy. For clarity, the images in this figure have been enlarged to show only the chromatin and pronuclei. A) Metaphase II oocytes were not treated (Aa–Ad) or extracted with 100 mM NaCl to remove soluble ORC2 and MCM7 (Ae–Ah). B) A zygote shortly after fertilization that was not extracted with salt. The maternal chromosomes are separating in anaphase II. Ba–Bd) Confocal planes at the separating chromosomes of the maternal anaphase II. Be–Bh) A different set of confocal planes showing the decondensing sperm nucleus of the same zygote shown in Ba–Bd. Note that the paternal DNA has no detectable MCM7 (Bg). C) Anaphase II zygote as in B but extracted with 100 mM NaCl to remove soluble ORC2 and MCM7. Ca–Cd) Maternal DNA. Ce–Ch) Recondensing sperm chromatin. This zygote had progressed slightly farther than the one in B, and now the paternal chromatin had MCM7 (Cg) but not ORC2 (Cf). Bar = 10 μm.