Figure 2.

Sperm contribution in fertilization and preimplantation embryo development. Several sperm-carried proteins are involved in acrosome reaction, binding to the zona pellucida (ZP), sperm‒oocyte fusion, and oocyte activation. Soon after sperm penetration into the oocyte, the sperm genome undergoes to global demethylation, much faster than the maternal genome. Embryonic Genome Activation (EGA), a process by which the embryo starts to produce its own transcripts, starts between the four-cell and eight-cell embryo stages. Before this phase, the embryo is sustained by the gametes’ transcriptome and proteome. A list of sperm-specific proteins has been identified in the embryo, in the up to eight-cell, morula, and blastocyst phases.