Figure 3

Cleavage furrow initiation and zygotic division in NHP zygotes with varying pronuclear orientations. (A1–A5) Rhesus zygote showing radially aligned apposed pronuclei with oblique orientation to the A → V axis 16 hrs post-ICSI (A1; polar body, Pb). Female pronuclear breakdown occurs first, around 20 hrs post-ICSI (A2). A meridional cleavage begins at the cortex overlying the site of the formerly intact MPn (A3: arrow), progressing asymmetrically through the cytoplasm to within 30° of the second polar body (Pb) on the opposing cortex (A4: arrow) 22 h post-ICSI. After division at 23 hrs post-ICSI, both Pb reside between the daughter blastomeres (A5). (B1–B5) A rhesus zygote with para-tangentially aligned cortical parental genomes oriented along the A → V axis 25 hrs post-ICSI (B1; polar body, Pb; inset, details of apposed pronucleus and the incorporated sperm axoneme, small arrows). At 27 hrs post-ICSI, pronuclear breakdown begins with the MPn (B2; MPn). Cleavage furrow initiation (B3: arrow) begins at the cortex overlying the site of the formerly intact MPn, progressing quickly through a meridional plane that includes the second polar body (B4: Pb). Cytokinesis at 30 hrs post-ICSI creates equal-sized daughter blastomeres with the polar bodies residing between the cleaved cells (B5: Pb; Nuc: daughter cell nucleus). (C1–C5) A cynomolgus ICSI zygote at 12 hrs post-ICSI showing apposed parental genomes aligned para-tangentially to the cortex and obliquely to the A → V axis (C1). The FPn undergoes breakdown first at 24 hrs post-ICSI (C2). However, cleavage furrow initiation at 26 hrs post-ICSI moves in an equatorial direction or right angle to the A → V axis (C3, straight arrow) while cortical membrane flow rotates both polar bodies into the developing furrow (C3, Pb, curved arrow depicts rotation direction). The bifurcated cleavage furrow progresses towards the opposite cortex (C4; arrows) as cytokinesis forms equal-sized daughter blastomeres with the polar bodies between daughter cells by 28.5 hrs post-ICSI (C5: polar bodies, Pb; Nuc: reconstituted daughter cell nuclei). All panels are HMC images taken from TLVM videos of ICSI fertilized zygotes undergoing first cleavage. Time in hours:minutes (h:m) post-ICSI. Bar = 20 μm.