Greet Cauffman

STEM CELLS, a peer reviewed journal published monthly, provides a forum for prompt publication of original investigative papers and concise reviews. STEM CELLS is read and written by clinical and basic scientists whose expertise encompasses the rapidly expanding fields of stem and progenitor cell biology. STEM CELLS welcomes original articles and concise reviews describing basic laboratory investigations of stem cells and the translation of their clinical aspects of characterization and manipulation from the bench to patient care. The journal covers all aspects of stem cells embryonic stem cells/induced pluripotent stem cells; tissue-specific stem cells; stem cell technology: epigenetics, genomics, proteomics, and metabonomics; cancer stem cells; translational and clinical research; and regenerative medicine.

In humans, the Deleted in Azoospermia Like (DAZL) gene is believed to function in the development of primordial germ cells and in germ cell differentiation and maturation because the expression of DAZL is only found in the germ and non-germ lineage of the reproductive system and in embryonic stem (ES) cells. The present study examined the presence of DAZL transcripts in the last stages of oocyte maturation, in ES cells, and throughout the preimplantation development; the link between gametes and ES cells. The finding of DAZL transcripts in the last stages of oogenesis and during the first two cell cycles of the preimplantation development was expected, because DAZL is a germ cell marker and the transcripts present at that time are generally encoded by the maternal genome. During the third cell cycle, DAZL showed a variable expression pattern, which may point to the maternal to embryonic transition. After the third cell cycle, transcripts were again consistently detected, suggesting embryonic DAZL transcription. In blastocysts, DAZL transcripts were only detected in those of good quality and this as well in the inner cell mass (ICM) as in the trophectoderm (TE). The presence of DAZL transcripts in the ICM and in ES cells was not surprising since both can lead to the formation of germ cells, but TE cells cannot. The quality-related expression of DAZL in blastocysts, and especially its trophectodermal expression, might imply other functions for DAZL beyond germ cell development.

The transcription factor OCT-4 is regarded as a critical factor in controlling mammalian early embryonic development because of its role in toti-/pluripotency. In human preimplantation embryos, OCT-4 studies are limited to RNA analysis of abnormally developing embryos. This study thoroughly investigated the expression pattern of OCT-4 throughout the human preimplantation development. Expression was examined by single-cell RT–PCR or indirect immunocytochemistry in 36 single oocytes of various maturity and 112 normally developing preimplantation embryos at the level of single blastomeres, morulas, blastocysts, or inner cell mass (ICM) and trophectoderm (TE) samples. Oocytes and cleavage stage embryos revealed a variable OCT-4 expression pattern, concomitant with a pure cytoplasmic localization of the protein. During compaction, the variability in expression faded away indicating embryonic OCT-4 expression and the protein appeared in the nucleus implying biological activity. In blastocysts, OCT-4 transcripts and proteins were present in the ICM and the TE. At protein level, blastocysts displayed different spatial expression patterns within a cell for the splice variants of OCT-4, which may endow them with different functional properties. As OCT-4 transcripts were also found in various differentiated cells, the presence of OCT-4 transcripts or proteins may not be sufficient for identifying undifferentiated cell lines in humans. Further, we suggest to examine the localization of OCT-4 proteins within a cell rather than to look for the presence and/or amount of transcripts.