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1.  Demarcation of Stable Subpopulations within the Pluripotent hESC Compartment 
PLoS ONE  2013;8(2):e57276.
Heterogeneity is a feature of stem cell populations, resulting from innate cellular hierarchies that govern differentiation capability. How heterogeneity impacts human pluripotent stem cell populations is directly relevant to their efficacious use in regenerative medicine applications. The control of pluripotency is asserted by a core transcription factor network, of which Oct4 is a necessary member. In mouse embryonic stem cells (ESCs), the zinc finger transcription factor Rex1 (Zfp42) closely tracks the undifferentiated state and is capable of segregating Oct4 positive mESCs into metastable populations expressing or lacking Rex1 that are inter-convertible. However, little is currently understood about the extent or function of heterogeneous populations in the human pluripotent compartment. Human ESCs express REX1 transcripts but the distribution and properties of REX1 expressing cells have yet to be described. To address these questions, we used gene targeting in human ESCs to insert the fluorescent protein Venus and an antibiotic selection marker under the control of the endogenous REX1 transcription regulatory elements, generating a sensitive, selectable reporter of pluripotency. REX1 is co-expressed in OCT4 and TRA-1-60 positive hESCs and rapidly lost upon differentiation. Importantly, REX1 expression reveals significant heterogeneity within seemingly homogenous populations of OCT4 and TRA-1-60 hESCs. REX1 expression is extinguished before OCT4 during differentiation, but, in contrast to the mouse, loss of REX1 expression demarcates a stable, OCT4 positive lineage-primed state in pluripotent hESCs that does not revert back to REX1 positivity under normal conditions. We show that loss of REX1 expression correlates with altered patterns of DNA methylation at the REX1 locus, implying that epigenetic mechanisms may interfere with the metastable phenotype commonly found in murine pluripotency.
doi:10.1371/journal.pone.0057276
PMCID: PMC3578859  PMID: 23437358
2.  Phosphatidate degradation: Phosphatidate phosphatases (lipins) and lipid phosphate phosphatases 
Biochimica et biophysica acta  2009;1791(9):956-961.
Summary
Three lipid phosphate phosphatases (LPPs) regulate cell signaling by modifying the concentrations of a variety of lipid phosphates versus their dephosphorylated products. In particular, the LPPs are normally considered to regulate signaling by the phospholipase D (PLD) pathway by converting phosphatidate (PA) to diacylglycerol (DAG). LPP activities do modulate the accumulations of PA and DAG following PLD activation, but this could also involve an effect upstream of PLD activation. The active sites of the LPPs are on the exterior surface of plasma membranes, or on the luminal surface of internal membranes. Consequently, the actions of the LPPs in metabolizing PA formed by PLD1 or PLD2 should depend on the access of this substrate to the active site of the LPPs. Alternatively, PA generated on the cytosolic surface of membranes should be readily accessible to the family of specific phosphatidate phosphatases, namely the lipins. Presently, there is only indirect evidence for the lipins participating in cell signaling following PLD activation. So far, we know relatively little about how individual LPPs and specific phosphatidate phosphatases (lipins) modulate cell signaling through controlling the turnover of bioactive lipids that are formed after PLD activation.
doi:10.1016/j.bbalip.2009.02.007
PMCID: PMC2875194  PMID: 19250975
Diacylglycerol; lysophosphatidate; phosphatidate; phospholipase D; triacylglycerol synthesis

Results 1-2 (2)