Beta-catenin-dependent or canonical Wnt signals are fundamental in animal development and tumor progression. Using Xenopus laevis, we report that the BTB/POZ zinc finger family member Kaiso directly represses canonical Wnt gene targets (Siamois, c-Fos, Cyclin-D1, and c-Myc) in conjunction with TCF/LEF (TCF). Analogous to beta-catenin relief of TCF repressive activity, we show that p120-catenin relieves Kaiso-mediated repression of Siamois. Furthermore, Kaiso and TCF coassociate, and combined Kaiso and TCF derepression results in pronounced Siamois expression and increased beta-catenin coprecipitation with the Siamois promoter. The functional interdependency is underlined by Kaiso suppression of beta-catenin-induced axis duplication and by TCF-3 rescue of Kaiso depletion phenotypes. These studies point to convergence of parallel p120-catenin/Kaiso and beta-catenin/TCF signaling pathways to regulate gene expression in vertebrate development and possibly carcinogenesis.

The recent identification of the genes responsible for several human genetic diseases affecting bone homeostasis and the characterization of mouse models for these diseases indicated that canonical Wnt signaling plays a critical role in the control of bone mass. Here, we report that the osteoblast-specific transcription factor Osterix (Osx), which is required for osteoblast differentiation, inhibits Wnt pathway activity. First, in calvarial cells of embryonic day (E)18.5 Osx-null embryos, expression of the Wnt antagonist Dkk1 was abolished, and that of Wnt target genes c-Myc and cyclin D1 was increased. Moreover, our studies demonstrated that Osx bound to and activated the Dkk1 promoter. In addition, Osx inhibited ␤-catenin-induced Topflash reporter activity and ␤-catenin-induced secondary axis formation in Xenopus embryos. Importantly, in calvaria of E18.5 Osx-null embryos harboring the TOPGAL reporter transgene, ␤-galactosidase activity was increased, suggesting that Osx inhibited the Wnt pathway in osteoblasts in vivo. Our data further showed that Osx disrupted binding of Tcf to DNA, providing a likely mechanism for the inhibition by Osx of ␤-catenin transcriptional activity. We also showed that Osx decreased osteoblast proliferation. Indeed, E18.5 Osx-null calvaria showed greater BrdU incorporation than wildtype calvaria and that Osx overexpression in C2C12 mesenchymal cells inhibited cell growth. Because Wnt signaling has a major role in stimulating osteoblast proliferation, we speculate that Osxmediated inhibition of osteoblast proliferation is a consequence of the Osx-mediated control of Wnt/␤-catenin activity. Our results add a layer of control to Wnt/␤-catenin signaling in bone.

Mutational alterations of the PTEN gene located on chromosome 10q23.3 have been frequently observed in a variety of human malignancies, including glioblastoma, melanoma, prostate cancer and endometrial cancer. 1-7 PTEN mutations and allelic deletions at 10q23 appear to be late events in glioblastoma, melanoma and prostate cancer, while in thyroid and endometrial cancers, PTEN alterations are found at an early stage, such as endometrial hyperplasia and benign thyroid tumors. 4 -9 Frequent germline or somatic mutations of PTEN have also been found in patients with Cowden disease and Bannayan-Zonana syndrome, which are autosomal dominant disorders characterized by the formation of multiple benign tumors and increased risk of malignant breast and thyroid tumors. 10,11 The PTEN gene encodes a protein product which shares high homology in its N-terminal region with the cytoskeletal protein tensin and the secretary vesicle protein auxilin. 1,2 The PTEN protein also contains a structural motif for a dual-specificity protein phosphatase. 12 PTEN acts as a phospholipid phosphatase, dephosphorylating PIP 3 with specificity for the phosphate group at the D3 position of the inositol ring. 13 PIP 3 is a lipid second messenger produced by PI3-kinase and activates a variety of signaling effectors such as AKT kinase. The lipid phosphatase activity of PTEN is essential for its ability to inhibit tumorigenesis and growth inhibition. 14,15 In human tumor cells lacking wild-type PTEN or in PTEN-deficient mice, PIP 3 levels are increased, leading to enhanced phosphorylation and activation of the survivalpromoting factor AKT kinase, indicating that PTEN exerts its tumor-suppressor function by negatively regulating the antiapoptotic PI3-kinase/AKT signaling pathway. 16 In addition, in immortalized PTEN-deficient mouse embryonic fibroblasts, PTEN restored apoptosis induced by stimuli such as UV irradiation. 17 The role of PTEN as a tumor-suppressor has also been attributed to its ability to modulate cell-cycle progression and cell motility. Expression of wild-type PTEN in PTEN-null glioblastoma or renal cell carcinoma cells causes cell-cycle arrest in the G 1 phase, inhibits colony formation and suppresses tumorigenicity in nude mice. 18 Exogenous expression of PTEN in fibroblasts and a glioma cell line with mutant PTEN alleles also suppresses cell migration, integrin-mediated cell spreading and focal adhesion. 19

Melt rheology and mechanical properties in linear low density polyethylene (LLDPE)/low density polyethylene (LDPE), LLDPE/high density polyethylene (HDPE), and HDPE/LDPE blends were investigated. All three blends were miscible in the melt, but the LLDPE/LDPE and HDPE/LDPE blends exibiled two crystallization and melting temperatures, indicating that those blends phase separated upon cooling from the melt. The melt strength of the blends increased with increasing molecular weight of the LDPE that was used. The mechanical properties of the LLDPE/LDPE blend were higher than claculated from a simple rule of mixtures, whiele those of the LLDPE/HDPE blend conformed to the rule of mixtures, but the properties of HDPE/LDPE were less than the rule of mixtures prediction.

Global transcriptional silencing is a highly conserved mechanism central to the oocyte-to-embryo transition. We report the unexpected discovery that global transcriptional silencing in oocytes depends on an mRNA decay activator. Oocyte-specific loss of ZFP36L2 an RNA-binding protein that promotes AU-rich element-dependent mRNA decay prevents global transcriptional silencing and causes oocyte maturation and fertilization defects, as well as complete female infertility in the mouse. Single-cell RNA sequencing revealed that ZFP36L2 downregulates mRNAs encoding transcription and chromatin modification regulators, including a large group of mRNAs for histone demethylases targeting H3K4 and H3K9, which we show are bound and degraded by ZFP36L2. Oocytes lacking Zfp36l2 fail to accumulate histone methylation at H3K4 and H3K9, marks associated with the transcriptionally silent, developmentally competent oocyte state. Our results uncover a ZFP36L2-dependent mRNA decay mechanism that acts as a developmental switch during oocyte growth, triggering wide-spread shifts in chromatin modification and global transcription.