Figure 2

Presence of histone H3.1/H3.2 in paternal chromatin derived from human sperm in mouse and human oocytes. Zygotes obtained after heterologous ICSI (a, b) and human multipronuclear zygotes acquired after artificial fertilisation (c, d) stained for H3.1/H3.2 (middle column) and DAPI, which labels DNA (right column); merges are depicted in the left column. Zygotes were obtained after heterologous ICSI and fixed respectively 60 minutes (a) and 150 minutes (b) after injection of human sperm. Arrow indicates maternal chromatin, arrowhead paternal chromatin and asterisk the polar bodies.c. Human tripronuclear zygote fixed 7 hours after performing ICSI. Tripronuclear zygotes derived from ICSI are likely to be a consequence of a failure in second polar body extrusion. Similar to maternal mouse chromatin, these pronuclei exhibit clear H3.1/H3.2 staining (indicated by arrows). H3.1/H3.2 is also present in the paternal pronuclei (indicated by arrowhead) though the obtained signal is lower. Asterisk indicates polar body. d. Human multipronuclear zygote fixed 22 hours after insemination with human sperm. Multipronuclear zygotes derived from IVF are likely formed by fusion of multiple sperm with an oocyte. The more intensely stained pronucleus (arrow) most likely represents the female nucleus since H3.1/H3.2 levels are higher in maternal chromatin [10].