<i>Setdb1</i>^<i>m-z+</i> zygotes show severe delays in pronuclear maturation and entry into the first mitosis.

<p><b>(A)</b> Schematic representation of the timing of cell cycle phases of 1-cell and 2-cell stage embryos. (<b>B, C</b>) Determination of pronuclear (PN) stages after <i>in vitro</i> fertilization. Met II oocytes from <i>Setdb1</i> KO and control mice were fertilized <i>in vitro</i> with sperm from WT mice, and at 5 hours post-fertilization (hpf), the zygotes (<i>Setdb1</i>^<i>m-z+</i> and <i>Setdb1</i>^<i>m+z+</i>, respectively) were stained with DAPI (blue) to determine their PN stages. <b>(B)</b> Representative zygotes at PN1, PN2, and PN3 stages. The boundaries of the zygotes are defined by circles, and the male and female pronuclei are indicated. Pb, polar body. Scale bars, 30 μm. <b>(C)</b> The percentages of PN1, PN2-3, and abnormal zygotes. The total numbers of embryos examined are indicated. (<b>D, E</b>) <i>Setdb1</i> KO and control females were mated with WT males, zygotes (<i>Setdb1</i>^<i>m-z+</i> and <i>Setdb1</i>^<i>m+z+</i>, respectively) collected at E0.5 were incubated in the presence of colcemid for 18 hours and then stained with DAPI to determine the cell cycle stages. <b>(D)</b> Representative zygotes at interphase and M phase. The boundaries of the zygotes are defined by circles. Pb, polar body. Scale bars, 30 μm. <b>(E)</b> The percentages of interphase, M phase, and abnormal zygotes. The total numbers of embryos examined are indicated.