Power and sample size simulations for Randomized Play-the-Winner rules

Response-adaptive randomization procedures, such as the Randomized Play-the-Winner (RPW), are treatment allocation rules for clinical trials that use available information on treatment outcomes to skew the allocation probability in favor of the treatment performing better thus far in the trial. Such allocation rules are based on the ethically desirable aim of reducing the share of patients allocated to the inferior treatment. This noble intent is overcome by statistical and logistical issues. One practical implementation obstacle of the RPW method is the estimation of required sample size and expected allocation shares. Unfortunately, this information is not readily available or easy to calculate. We present simulation results to provide a realistic assessment of the power and sample size required for successful implementation of the RPW rule for a study with primary outcome variable that is binary. Additionally, we discuss some practical approaches for sample size determination based on the RPW.     

Adenomatous polyposis coli (APC) protein regulates epithelial cell migration and morphogenesis via PDZ domain-based interactions with plasma membranes

The tumor suppressor adenomatous polyposis coli (APC) protein is localized at the plus ends of microtubules (MTs) at the migrating edges of cells. Here, we established Xenopus A6 epithelial cell transfectants expressing GFP-fused full-length APC (GFP-fAPC) or truncated APC lacking the COOH-terminal PDZ-binding motif TSV (GFP-APC(DeltaTSV)). Although both APC proteins were similarly accumulated at the MT ends, GFP-fAPC, but not GFP-APC(DeltaTSV), was associated with the basal and lateral plasma membranes and co-localized with a PDZ protein, DLG1. Stable over-expression of GFP-fAPC enforced cell-substrate attachment and thereby enhanced cell spreading on the substratum and induced polarized extension of lamellipodia and MTs during scratch-induced migration. Truncation of the PDZ-binding motif was sufficient to abolish these effects of GFP-fAPC. Furthermore, expression of GFP-APC(DeltaTSV) disturbed the establishment of a continuous epithelial monolayer. These results suggest that APC links MTs to plasma membranes through interactions with PDZ proteins, such that the migration and morphogenesis of epithelial cells can be properly regulated.     

Epigenetic regulation of Nanog gene in embryonic stem and trophoblast stem cells

The Nanog and Oct-4 genes are essential for maintaining pluripotency of embryonic stem (ES) cells and early embryos. We previously reported that DNA methylation and chromatin remodeling underlie the cell type-specific mechanism of Oct-4 gene expression. In the present study, we found that there is a tissue-dependent and differentially methylated region (T-DMR) in the Nanog up-stream region. The T-DMR is hypomethylated in ES cells, but is heavily methylated in trophoblast stem (TS) cells and NIH/3T3 cells, in which the Nanog gene is repressed. Furthermore, in vitro methylation of T-DMR suppressed Nanog promoter activity in reporter assay. Chromatin immunoprecipitation assay revealed that histone H3 and H4 are highly acetylated, and H3 lysine (K) 4 is hypermethylated at the Nanog locus in ES cells. Conversely, histone deacetylation and H3-K4 demethylation occurred in TS cells. Importantly, in TS cells, hypermethylation of H3-K9 and -K27 is found only at the Nanog locus, not the Oct-4 locus, indicating that the combination of histone modifications associated with the Nanog gene is distinct from that of the Oct-4 gene. In conclusion, the Nanog gene is regulated by epigenetic mechanisms involving DNA methylation and histone modifications.