17,456 research outputs found
An Opposite Effect of the CDK Inhibitor, p18<sup>INK4c</sup> on Embryonic Stem Cells Compared with Tumor and Adult Stem Cells
Self-renewal is a feature common to both adult and embryonic stem (ES) cells, as well as tumor stem cells (TSCs). The cyclin-dependent kinase inhibitor, p18INK4c, is a known tumor suppressor that can inhibit self-renewal of tumor cells or adult stem cells. Here, we demonstrate an opposite effect of p18 on ES cells in comparison with teratoma cells. Our results unexpectedly showed that overexpression of p18 accelerated the growth of mouse ES cells and embryonic bodies (EB); on the contrary, inhibited the growth of late stage teratoma. Up-regulation of ES cell markers (i.e., Oct4, Nanog, Sox2, and Rex1) were detected in both ES and EB cells, while concomitant down-regulation of various differentiation markers was observed in EB cells. These results demonstrate that p18 has an opposite effect on ES cells as compared with tumor cells and adult stem cells. Mechanistically, expression of CDK4 was significantly increased with overexpression of p18 in ES cells, likely leading to a release of CDK2 from the inhibition by p21 and p27. As a result, self-renewal of ES cells was enhanced. Our current study suggests that targeting p18 in different cell types may yield different outcomes, thereby having implications for therapeutic manipulations of cell cycle machinery in stem cells. Β© 2012 Li et al
Channel Estimation and Uplink Achievable Rates in One-Bit Massive MIMO Systems
This paper considers channel estimation and achievable rates for the uplink
of a massive multiple-input multiple-output (MIMO) system where the base
station is equipped with one-bit analog-to-digital converters (ADCs). By
rewriting the nonlinear one-bit quantization using a linear expression, we
first derive a simple and insightful expression for the linear minimum
mean-square-error (LMMSE) channel estimator. Then employing this channel
estimator, we derive a closed-form expression for the lower bound of the
achievable rate for the maximum ratio combiner (MRC) receiver. Numerical
results are presented to verify our analysis and show that our proposed LMMSE
channel estimator outperforms the near maximum likelihood (nML) estimator
proposed previously.Comment: 5 pages, 2 figures, the Ninth IEEE Sensor Array and Multichannel
Signal Processing Worksho
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