Stage-Specific Germ-Cell Marker Genes Are Expressed in All Mouse Pluripotent Cell Types and Emerge Early during Induced Pluripotency

Abstract

Embryonic stem cells (ESCs) generated from the in-vitro culture of blastocyst stage embryos are known as equivalent to blastocyst inner cell mass (ICM) in-vivo. Though several reports have shown the expression of germ cell/pre-meiotic (GC/PrM) markers in ESCs, their functional relevance for the pluripotency and germ line commitment are largely unknown. In the present study, we used mouse as a model system and systematically analyzed the RNA and protein expression of GC/PrM markers in ESCs and found them to be comparable to the expression of cultured pluripotent cells originated from the germ line. Further, siRNA knockdown experiments have demonstrated the parallel maintenance and independence of pluripotent and GC/PrM networks in ESCs. Through chromatin immunoprecipitation experiments, we observed that pluripotent cells exhibit active chromatin states at GC marker genes and a bivalent chromatin structure at PrM marker genes. Moreover, gene expression analysis during the time course of iPS cells generation revealed that the expression of GC markers precedes pluripotency markers. Collectively, through our observations we hypothesize that the chromatin state and the expression of GC/PrM markers might indicate molecular parallels between in-vivo germ cell specification and pluripotent stem cell generation.

Conversion of genomic imprinting by reprogramming and redifferentiation

“…Our data demonstrated that reprogramming of parthenogenetic somatic cells could change the DNA methylation and gene expression status of Snrpn and Ndn. Recent studies have shown that mouse germ cell markers are expressed during induced pluripotency (Xu et al, 2011) and that the Snrpn imprint is erased in fetal germ cells (Smith et al, 2011), which could be an explanation for why erasure or partial erasure of the imprint occurs in mouse miPSCs. Furthermore, alterations in DNA methylation of imprinted genes are maintained when the reprogrammed cells are differentiated into specialized cell types.…”

Lrrc34, a Novel Nucleolar Protein, Interacts withNpm1andNcland Has an Impact on Pluripotent Stem Cells

“…Very recently, Leitch and Smith postulated that germ cells represent a continuous cycle of pluripotency distinguishable just by a naive state in the epiblast and a latent in the germline but not through the expression of pluripotency-regulating genes [25]. Indeed, we could also show that germ cell marker genes are expressed in pluripotent stem cells and arise early in reprogramming [20]. Since Lrrc34 expression arises also very early in the reprogramming time course, it can be a hint for both pluripotency regulator and germ cell gene.…”

“…2B). Since all the results till now fit with our hypothesis that Lrrc34 might play a role in establishment and maintenance of pluripotency, we analyzed Lrrc34 expression during the time course of reprogramming by qRT-PCR (samples used for this study are described in [20] Supplementary Fig. S2).…”

The reciprocal relationship between primordial germ cells and pluripotent stem cells

“…Several lines of evidence provoked the hypothesis that ESCs might derive from PGC-like cells present in the ICM outgrowth. First, explanted cells from the ICM transiently express PGCrelated genes, including Blimp1, Prdm14, Stella, Fragilis, Lin28, c-kit, and Mvh [75,77,78]. Second, specified PGCs are the only cells in the early embryo that maintain (Oct4 and Nanog) or reacquire (Sox2) the expression of pluripotency-associated genes.…”

“…With this information in mind, it would be interesting to ask if also the generation of iPSCs from fibroblasts might pass through a germ celllike state. Indeed, it was found that the PGC markers Blimp1, Stella, and Fragilis start to express earlier after viral transduction than pluripotency markers [77]. However, further work is needed to fully understand the significance of this observation.…”