Analysis of Oct-4 expression and ploidy in individual human blastomeres

Oct-4, a decisive factor that maintains totipotency in murine embryonic and germ cells, is exclusively expressed in such cells, In mice, different lev els of oct-4 expression in blastomeres predict development towards inner ce ll mass (ICM) thigh oct-4) or trophectoderm (TE) (low oct-4). To address wh ether the mouse model also applies to human embryos, the cytoplasm of indiv idual human blastomeres from normally and abnormally fertilized embryos was tested for Oct-4 expression by reverse transcription-polymerase chain reac tion (RT-PCR). The nuclei of the same blastomeres were subjected to fluores cence in-situ hybridization (FISH) to determine ploidy. A significant diffe rence in Oct-4 mRNA levels was revealed between blastomeres, The distributi on of blastomeres with high Oct-4 levels varied according to the cleavage s tage of the embryo: the more blastomeres, the lower the percentage with hig h Oct-4 levels. Aneuploid blastomeres did not exhibit lower Oct-4 mRNA leve ls than diploid ones, Thus, differential Oct-4 expression in individual hum an blastomeres appears to direct cells towards the ICM or TE lineages witho ut regard to chromosomal status. Oct-4 might be used as a marker in preimpl antation genetic diagnosis to identify embryogenic blastomeres.