Oocytes are unique cells with the inherent capability to reprogram nuclei. The reprogramming of the somatic nucleus from its original cellular state to a totipotent state is essential for term development after somatic cell nuclear transfer. The nuclear-associated factors contained within oocytes are critical for normal fertilization by sperm or for somatic cell nuclear reprogramming. The chromatin of somatic nuclei can be reprogrammed by factors in the egg cytoplasm whose natural function is to reprogram sperm chromatin. The oocyte first obtains its reprogramming capability in the early fetal follicle, and then its capacity is enriched in the late growth phase and reaches its highest capability for reprogramming as fully-grown germinal vesicle oocytes. The cytoplasmic milieu most likely contains all of the specific transcription and/or reprogramming factors necessary for cellular reprogramming. Certain transcription factors in the cytoplast may be critical as has been demonstrated for induced pluripotent stem cells. The maternal pronucleus exerts a predominant, transcription-dependent effect on embryo cytofragmentation, with a lesser effect imposed by the ooplasm and the paternal pronucleus. With deep analysis of transcriptomics in oocytes and early developmental stage embryos more maternal transcription factors inducing cellular reprogramming will be identified.