Lack of Na+,K+-ATPase expression in intercalated cells may be compensated by Na+-ATPase: A study on MDCK – C11 cells

The lack of Na⁺,K⁺-ATPase expression in intercalated cells (IC) is an intriguing condition due to its fundamental role in cellular homeostasis. In order to better understand this question we compared the activities of Na⁺,K⁺-ATPase and Na⁺-ATPase in two MDCK cell clones: the C11, with IC characteristics, and the C7, with principal cells (PC) characteristics. The Na⁺,K⁺-ATPase activity found in C11 cells is far lower than in C7 cells and the expression of its β-subunit is similar in both cells. On the other hand, a subset of C11 without α-subunit expression has been found. In C11 cells the Na⁺-ATPase activity is higher than that of the Na⁺,K⁺-ATPase, and it is increased by medium alkalinization, suggesting that it could account for the cellular Na⁺-homeostasis. Although further studies are necessary for a better understanding of these findings, the presence of Na⁺-ATPase may explain the adequate survival of cells that lack Na⁺,K⁺-ATPase. Received 09 July 2008; received after revision 03 August 2008; accepted 12 August 2008     

Estimating and forecasting the long‐memory parameter in the presence of periodicity

We consider one parametric and five semiparametric approaches to estimate D in SARFIMA (0, D, 0)_s processes, that is, when the process is a fractionally integrated ARMA model with seasonality s. We also consider h‐step‐ahead forecasting for these processes. We present the proof of some features of this model and also a study based on a Monte Carlo simulation for different sample sizes and different seasonal periods. We compare the different estimation procedures analyzing the bias, the mean squared error values, and the confidence intervals for the estimators. We also consider three different methods to choose the total number of regressors in the regression analysis for the semiparametric class of estimation procedures. We apply the methodology to the Nile River flow monthly data, and also to a simulated seasonal fractionally integrated time series. Copyright © 2007 John Wiley & Sons, Ltd.     

RNA polymerase II C-terminal repeat influences response to transcriptional enhancer signals

The large subunit of RNA polymerase II contains a highly conserved and essential heptapeptide repeat (Pro-Thr-Ser-Pro-Ser-Tyr-Ser) at its carboxy terminus. Saccharomyces cerevisiae cells are inviable if their RNA polymerase II large subunit genes encode fewer than 10 complete heptapeptide repeats; if they encode 10 to 12 complete repeats cells are temperature-sensitive and cold-sensitive, but 13 or more complete repeats will allow wild-type growth at all temperatures. Cells containing C-terminal domains (CTDs) of 10 to 12 complete repeats are also inositol auxotrophs. The phenotypes associated with these CTD mutations are not a consequence of an instability of the large subunit; rather, they seem to reflect a functional deficiency of the mutant enzyme. We show here that partial deletion mutations in RNA polymerase II CTD affect the ability of the enzyme to respond to signals from upstream activating sequences in a subset of promoters in yeast. The number of heptapeptide repeats required for maximal response to signals from these sequences differs from one upstream activating sequence to another. One of the upstream elements that is sensitive to truncations of the CTD is the 17-base-pair site bound by the GAL4 transactivating factor.     

Derivation of pluripotent epiblast stem cells from mammalian embryos

Although the first mouse embryonic stem (ES) cell lines were derived 25 years ago using feeder-layer-based blastocyst cultures, subsequent efforts to extend the approach to other mammals, including both laboratory and domestic species, have been relatively unsuccessful. The most notable exceptions were the derivation of non-human primate ES cell lines followed shortly thereafter by their derivation of human ES cells. Despite the apparent common origin and the similar pluripotency of mouse and human embryonic stem cells, recent studies have revealed that they use different signalling pathways to maintain their pluripotent status. Mouse ES cells depend on leukaemia inhibitory factor and bone morphogenetic protein, whereas their human counterparts rely on activin (INHBA)/nodal (NODAL) and fibroblast growth factor (FGF). Here we show that pluripotent stem cells can be derived from the late epiblast layer of post-implantation mouse and rat embryos using chemically defined, activin-containing culture medium that is sufficient for long-term maintenance of human embryonic stem cells. Our results demonstrate that activin/Nodal signalling has an evolutionarily conserved role in the derivation and the maintenance of pluripotency in these novel stem cells. Epiblast stem cells provide a valuable experimental system for determining whether distinctions between mouse and human embryonic stem cells reflect species differences or diverse temporal origins.