Markers that define stemness in ESC are unable to identify the totipotent cells in human preimplantation embryos

Research output: Contribution to journalMeeting abstract (Journal)

Abstract

Introduction: NANOG, SOX2, and SALL4 are transcription factors that play a key role in controlling stemness in embryonic stem cells (ESC) and are therefore candidate markers for developmental triggers in early embryos. KRT18, a trophoblast determining gene, may mark early differentiation in embryos. The expression pattern of NANOG, SOX2, SALL4 and KRT18 may identify the totipotent cells during early human development and determine when early embryonic cells lose their totipotent competence.
Material and Methods: Thirtheen human oocytes and 121 human preimplantation embryos were examined for the presence of NANOG, SOX2, SALL4 or KRT18 proteins using immunostaining and confocal microscopy.
Results: None of the stemness markers seemed to direct the dividing blastomeres towards the inner cell mass (ICM) or trophectoderm (TE) lineage, nor could they identify all and none other than the totipotent cells during human preimplantation development. NANOG proteins could at the earliest be detected at the blastocyst stage and were consistently present in expanded blastocysts, when the two cell lineages were already visibly defined. Within the expanded blastocyst, we found NANOG proteins to be present in the nuclei of a subpopulation of the ICM. A sporadic NANOG expression was also detected in a minority of TE cells located near the ICM. A cytoplasmic SOX2 expression was detected in oocytes and throughout the whole preimplantation development. A nuclear expression appeared at day three of development and became prominent in all cells. After the ICM and the TE could clearly be distinguished, the nuclear staining increased in all cells of the ICM and disappeared in nearly all TE cells. SALL4 proteins were detected in the nucleus and the cytoplasm in oocytes and early cleavage stages until day 3 of development. During further development, the cytoplasmic staining was lost whereas the nuclear staining increased. In blastocysts, a strong expression was found in the nuclei of the ICM and TE. A joint expression of NANOG, SOX2 and SALL4 was only detected in the nuclei of a subpopulation of ICM cells. Expression of KRT18 was seen for the first time during compaction in some outer cells. During blastocyst expansion, KRT18 proteins were found in the cytoskeleton of the TE and the outer cells of the ICM adjacent to the blastocoel cavity, which will contribute to the yolk sac.
Conclusions: The expression pattern of markers that define stemness in ESC could not tell us when and in which cells totipotency is lost during early human development. However, because stemness markers act in concert to keep the properties of ESC, these markers may maintain totipotency in a subpopulation of the ICM. Assessing the presence of KRT18 proteins implied that the outer cells of compacting embryos have lost their totipotent competence prior to any visible morphological differentiation. KRT18 may be used as an early marker of differentiation during human preimplantation development.
Original languageEnglish
Pages (from-to)111-111
Number of pages1
JournalHum Reprod
Volume23
Issue numberJuly
Publication statusPublished - Jul 2008
EventFinds and Results from the Swedish Cyprus Expedition: A Gender Perspective at the Medelhavsmuseet - Stockholm, Sweden
Duration: 21 Sep 200925 Sep 2009

Keywords

  • human preimplantation embryo
  • embryonic stem cells

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