POU5F1 isoforms show different expression patterns in human embryonic stem cells and preimplantation embryos

¹ Research Center Reproduction and Genetics, University Hospital and Medical School of the 'Vrije Universiteit Brussel' (Free University of Brussels), Brussels, Belgium
² Research Center Reproduction and Genetics, University Hospital and Medical School of the 'Vrije Universiteit Brussel' (Free University of Brussels), Brussels, Belgium; Center for Medical Genetics, University Hospital and Medical School of the 'Vrije Universiteit Brussel' (Free University of Brussels), Brussels, Belgium
³ Research Center Reproduction and Genetics, University Hospital and Medical School of the 'Vrije Universiteit Brussel' (Free University of Brussels), Brussels, Belgium; Center for Reproductive Medicine, University Hospital and Medical School of the 'Vrije Universiteit Brussel' (Free University of Brussels), Brussels, Belgium

^* To whom correspondence should be addressed. E-mail: gcauffma{at}az.vub.ac.be.

	Abstract

The contribution of the POU domain, class 5, transcription factor 1 (POU5F1) in maintaining totipotency in human embryonic stem (hES) cells has been repeatedly proven. In humans, two isoforms are encoded: POU5F1_iA and POU5F1_iB. So far, no discrimination has been made between the isoforms in POU5F1 studies and it is unknown which isoform contributes to the undifferentiated phenotype. Using immunocytochemistry, expression of POU5F1_iA and POU5F1_iB was examined in hES cells and all stages of human preimplantation development to look for differences in expression, biological activity and relation to totipotency. POU5F1_iA and POU5F1_iB displayed different temporal and spatial expression patterns. During human preimplantation development, a significant POU5F1_iA expression was seen in all nuclei of compacted embryos and blastocysts and a clear POU5F1_iB expression was detected from the four-cell stage onwards in the cytoplasm of all cells. The cytoplasmic localization might imply no or other biological functions beyond transcription activation for POU5F1_iB. The stemness properties of POU5F1 can be assigned to POU5F1_iA because hES cells expressed POU5F1_iA but not POU5F1_iB. However, POU5F1_iA is not the appropriate marker to identify totipotent cells because POU5F1_iA was also expressed in the non-totipotent trophectoderm and was not expressed in zygotes and early cleavage stage embryos, which are assumed to be totipotent. POU5F1_iA's expression pattern may suggest that POU5F1_iA alone cannot sustain totipotency and that co-expression with other stemness factors might be the key to totipotency.

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