Figure 1.—

Phenotypes of such-1(t1668) embryos: still images from time-lapse DIC recordings; time relative to onset of NEBD in min:sec. Anterior or polar body position is left in this and other figures. Bar, 10 μm. Asterisks, pronuclei (female left, male right); black arrowheads, spindle poles; white arrowhead, center of monopolar configuration. See also File S1, File S2, File S3, File S4. (A) (−5:00): wild-type embryo with one female and one male pronucleus; a pseudocleavage furrow forms. (+2:30) A bipolar spindle assembles during mitosis. (+9:00) The first division gives rise to a larger anterior AB cell and a smaller posterior P₁ cell. (B–D) such-1(t1668) embryos classified according to the number of pronuclei and the presence of centrosomes. All embryos examined contain a single female pronucleus with normal size. N = 38; percentages on the right indicate the fraction of embryos within each class. (B) (−5:00) Class I embryos possess one male and one female pronucleus; a pseudocleavage furrow forms. (+2:30) These embryos assemble a spindle that is bipolar (5/11) or multipolar (6/11; not shown, presumably when supernumerary centrioles were contributed by the sperm). (+9:00) All class I embryos divide. (C) (−5:00) Class II embryos have a female pronucleus, but no male pronucleus; pseudocleavage occurs. (+2:30) Centrosomes are present and form either a bipolar spindle (10/21) or a multipolar spindle (6/21; not shown). Sometimes the spindle appears monopolar initially, with strong microtubule nucleation from the MTOC, but resolves within the same prolonged cell cycle into a bipolar spindle (5/21; not shown), possibly reflecting a defect in the timing of centriole disengagement. (+9:00) All class II embryos divide. (D) (−5:00) Class III embryos have a female pronucleus, but no male pronucleus; no pseudocleavage occurs. (+2:30) MTOCs are absent and embryos undergo monopolar mitosis, with microtubules nucleated weakly around the chromatin (6/6; see also Figure 2C). (+9:00) Embryos are still in mitosis and fail to divide even after NER and exit from mitosis (see File S4).