PMID:15183310

Citation	Liu, L, Czerwiec, E and Keefe, DL (2004) Effect of ploidy and parental genome composition on expression of Oct-4 protein in mouse embryos. Gene Expr. Patterns 4:433-41
Abstract	The transcription factor Oct-4 is expressed in germ cells and also is considered as a marker for pluripotency of stem cells. We first examined dynamics of Oct-4 protein expression during preimplantation development using both Western blot analysis, and immunofluorescence staining. We show that intact Oct-4 protein is not detected in either ovulated mature oocytes, or in zygotes and 2-4-cell embryos, which are the only known totipotent cell types in mammals. This finding is unexpected, since Oct-4 has been proposed to play a role in the control of totipotency. The results suggest that Oct-4 is not indispensable for fertilization and early cleavage. Rather, expression of Oct-4 protein is first detected in the nuclei of 8-16 cell morula, increases in early blastocysts, and declines in late blastocysts, in which most Oct-4 protein is confined to the inner cell mass (ICM) region, consistent with previous findings. We further compared Oct-4 protein expression in diploid and tetraploid blastocysts derived from normal fertilization or parthenogenesis, as well as expression in diploid androgenetic blastocysts. Expression levels and localization of Oct-4 protein are similar in both diploid and tetraploid early blastocysts, regardless of whether blastocysts are derived from fertilization or parthenogenesis. Androgenetic diploid blastocysts also express similar levels of Oct-4. Late blastocysts generated by both fertilization and parthenogenesis show a similar pattern of Oct-4 expression, suggesting that paternal genome activation is not required for Oct-4 expression. Expression of Oct-4 protein does not differ between diploid and tetraploid embryos, indicating that tetraploidy does not influence Oct-4 expression. Thus, expression of Oct-4 protein is initiated at morula stage in preimplantation embryos and completely controlled by a mechanism activated in oocytes. Downregulation of Oct-4 expression coincides with differentiation of trophectoderm. Similar profiles of Oct-4 expression observed in embryos with different ploidy and genome composition, are suggestive of Oct-4 being necessary but not sufficient for developmental potency.
Links	PubMed Online version:10.1016/j.modgep.2004.01.004
Keywords	Animals; Blastocyst/metabolism; Blastomeres/metabolism; DNA-Binding Proteins/biosynthesis; DNA-Binding Proteins/genetics; Female; Gene Expression Regulation, Developmental/genetics; Gene Expression Regulation, Developmental/physiology; Mice; Morula/metabolism; Octamer Transcription Factor-3; Parthenogenesis/physiology; Polyploidy; Pregnancy; Transcription Factors/biosynthesis; Transcription Factors/genetics; Trophoblasts/metabolism; Zygote/metabolism
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