Embryonic stem (ES) cells derived from the inner cell mass (ICM) of blastocysts grow infinitely while maintaining pluripotency. Leukemia inhibitory factor (LIF) can maintain self-renewal of mouse ES cells through activation of Stat3. However, LIF/Stat3 is dispensable for maintenance of ICM and human ES cells, suggesting that the pathway is not fundamental for pluripotency. In search of a critical factor(s) that underlies pluripotency in both ICM and ES cells, we performed in silico differential display and identified several genes specifically expressed in mouse ES cells and preimplantation embryos. We found that one of them, encoding the homeoprotein Nanog, was capable of maintaining ES cell self-renewal independently of LIF/Stat3. nanog-deficient ICM failed to generate epiblast and only produced parietal endoderm-like cells. nanog-deficient ES cells lost pluripotency and differentiated into extraembryonic endoderm lineage. These data demonstrate that Nanog is a critical factor underlying pluripotency in both ICM and ES cells.
We report the effect of mixing three rare-earth (RE) elements in the RE site on the superconducting properties of melt-processed REBa 2 Cu 3 O y , in which RE elements are selected from the group of Nd, Sm, Eu and Gd. The heat treatment profiles for melt processing were determined according to the peritectic decomposition temperatures obtained from the thermal analysis measurements. Microstructural observations and compositional analysis showed that the main phase was (R1 0.33 R2 0.33 R3 0.33 )Ba 2 Cu 3 O y , in which the ratio of three RE elements (R1, R2, R3) was equal to that of the nominal composition, indicating that mixing of RE elements was uniform. All the samples showed relatively high T c in the range 93.1-95.3 K and exhibited the secondary peak effect in the magnetization curves at 77 K with the irreversibility field higher than that of melt-processed Y-Ba-Cu-O. A high J c value of 50 000 A cm −2 at 77 K and 2 T was achieved in (Nd, Eu, Gd)Ba 2 Cu 3 O y for field parallel to the c-axis.
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