The mammalian oocyte possesses powerful reprogramming factors, which can reprogram terminally differentiated germ cells (sperm) or somatic cells within a few cell cycles. Although it has been suggested that use of oocyte-derived transcripts may enhance the generation of induced pluripotent stem cells, the reprogramming factors in oocytes are undetermined, and even the identified proteins composition of oocytes is very limited. In the present study, 7,000 mouse oocytes at different developmental stages, including the germinal vesicle stage, the metaphase II (MII) stage, and the fertilized oocytes (zygotes), were collected. We successfully identified 2,781 proteins present in germinal vesicle oocytes, 2,973 proteins in MII oocytes, and 2,082 proteins in zygotes through semiquantitative MS analysis. Furthermore, the results of the bioinformatics analysis indicated that different protein compositions are correlated with oocyte characteristics at different developmental stages. For example, specific transcription factors and chromatin remodeling factors are more abundant in MII oocytes, which may be crucial for the epigenetic reprogramming of sperm or somatic nuclei. These results provided important knowledge to better understand the molecular mechanisms in early development and may improve the generation of induced pluripotent stem cells.germinal vesicle | metaphase II | zygote | protein | reprogramming R eprogramming of patient-specific somatic cells into pluripotent stem cells has attracted wide scientific and public interest because of the great potential value in both research and therapy. Recent advances in induced pluripotent stem cell (iPSC) research have clearly indicated that a small number of transcription factors can reverse the cell fate of differentiated somatic cells; however, the reprogramming process remains slow, and the efficiency is low. Typically, 1% of cells are reprogrammed, but this process requires at least 7 d to 2 wk (1-8). In contrast, reprogramming during somatic cell nuclear transfer (SCNT) occurs within one or two cell cycles and often in a majority of embryos (9-14). The oocytederived transcripts that promote this more efficient reprogramming remain unidentified; however, it has been suggested that their inclusion with the four transcription factors (Oct4, Sox2, Klf4, and c-Myc) may increase the speed and efficiency of the reprogramming process (15). As a step to identification of these factors, this project sought to define the proteome of mouse oocytes at three stages of development, which will also provide us important information on the factors regulating developmental competence of oocytes.During mammalian oogenesis, the oocyte undergoes two cell cycle arrests at the dictyate or germinal vesicle (GV) stage and the metaphase II (MII) stage (16,17). MII oocytes have been widely used to reprogram somatic cell nuclei, because during normal reproduction, sperm and oocyte nuclei are reprogrammed by the MII oocyte to produce totipotent zygotes. By contrast, results from our previous nucl...
