A large number of retrotransposons are expressed when the zygotic genome is first transcribed, including the endogenous retroviruses (ERVs), LINE-1 elements, and the non-autonomous SINE elements. At the 2C stage, MuERV-L/MERVL retrovirus-like elements are transiently de-repressed and produce 3% of the transcribed mRNAs. Following the 2C stage, MERVL-retroelement expression is silenced. The newly study discovered that this regulated pattern of MERVL expression overlapped with greater than one hundred 2C-specific genes that have co-opted regulatory elements from these foreign retroviruses to initiate their transcription.