Dazap2 is required for FGF-mediated posterior neural patterning, independent of Wnt and Cdx function

Selective gene-expression profiling of migratory tumor cells in vivo predicts clinical outcome in breast cancer patients

Introduction

Metastasis of breast cancer is the main cause of death in patients. Previous genome-wide studies have identified gene-expression patterns correlated with cancer patient outcome. However, these were derived mostly from whole tissue without respect to cell heterogeneity. In reality, only a small subpopulation of invasive cells inside the primary tumor is responsible for escaping and initiating dissemination and metastasis. When whole tissue is used for molecular profiling, the expression pattern of these cells is masked by the majority of the noninvasive tumor cells. Therefore, little information is available about the crucial early steps of the metastatic cascade: migration, invasion, and entry of tumor cells into the systemic circulation.

Methods

In the past, we developed an in vivo invasion assay that can capture specifically the highly motile tumor cells in the act of migrating inside living tumors. Here, we used this assay in orthotopic xenografts of human MDA-MB-231 breast cancer cells to isolate selectively the migratory cell subpopulation of the primary tumor for gene-expression profiling. In this way, we derived a gene signature specific to breast cancer migration and invasion, which we call the Human Invasion Signature (HIS).

Results

Unsupervised analysis of the HIS shows that the most significant upregulated gene networks in the migratory breast tumor cells include genes regulating embryonic and tissue development, cellular movement, and DNA replication and repair. We confirmed that genes involved in these functions are upregulated in the migratory tumor cells with independent biological repeats. We also demonstrate that specific genes are functionally required for in vivo invasion and hematogenous dissemination in MDA-MB-231, as well as in patient-derived breast tumors. Finally, we used statistical analysis to show that the signature can significantly predict risk of breast cancer metastasis in large patient cohorts, independent of well-established prognostic parameters.

Conclusions

Our data provide novel insights into, and reveal previously unknown mediators of, the metastatic steps of invasion and dissemination in human breast tumors in vivo. Because migration and invasion are the early steps of metastatic progression, the novel markers that we identified here might become valuable prognostic tools or therapeutic targets in breast cancer.

The effects of promoter methylation on downregulation of DAZAP2 in multiple myeloma cell lines

Our previous studies had shown that DAZAP2 was profoundly downregulated in bone marrow mononuclear cells from multiple myeloma patients. In this report, we analyzed epigenetic changes in multiple myeloma cell lines to understand the molecular mechanisms underlying the downregulation of DAZAP2. Four multiple myeloma cell lines, KM3, MM.1S, OPM-2 and ARH-77, were studied. The results of methylation specific PCR (MSP) showed that the promoter of DAZAP2 was methylated for KM3, MM.1S, OPM-2 and unmethylated for ARH-77. The DAZAP2 promoter region was amplified to obtain a series of different length sequences. All of the amplified sequences were inserted to luciferase reporter vector. The constructs were transfected into COS-7 cells and the luciferase activities were measured to search for the core region of DAZAP2 promoter. Two CpG islands were found in DAZAP2 promoter region. The results of luciferase assay showed that CpG island 1 displayed weak transcriptional activity, whereas CpG island 2 exhibited strong transcriptional activity (273 folds) compared to the control. The sequence that covered both CpG islands 1 and 2 showed higher activity (1,734 folds) compared to the control, suggesting that the two islands had synergistic effect on regulating DAZAP2 expression. We also found that M. Sss I methylase could inhibit the luciferase activity, whereas demethylation using 5-aza-2′-deoxycytidine treatment rescued the expression of DAZAP2 for multiple myeloma cell lines. These data revealed that methylation of DAZAP2 promoter was involved in downregulation of DAZAP2 in multiple myeloma cells.

Genome-wide identification of microRNA targets in human ES cells reveals a role for miR-302 in modulating BMP response

MicroRNAs are important regulators in many cellular processes, including stem cell self-renewal. Recent studies demonstrated their function as pluripotency factors with the capacity for somatic cell reprogramming. However, their role in human embryonic stem (ES) cells (hESCs) remains poorly understood, partially due to the lack of genome-wide strategies to identify their targets. Here, we performed comprehensive microRNA profiling in hESCs and in purified neural and mesenchymal derivatives. Using a combination of AGO cross-linking and microRNA perturbation experiments, together with computational prediction, we identified the targets of the miR-302/367 cluster, the most abundant microRNAs in hESCs. Functional studies identified novel roles of miR-302/367 in maintaining pluripotency and regulating hESC differentiation. We show that in addition to its role in TGF-β signaling, miR-302/367 promotes bone morphogenetic protein (BMP) signaling by targeting BMP inhibitors TOB2, DAZAP2, and SLAIN1. This study broadens our understanding of microRNA function in hESCs and is a valuable resource for future studies in this area.

The Pax3 and Pax7 paralogs cooperate in neural and neural crest patterning using distinct molecular mechanisms, in Xenopus laevis embryos

Pax3 and Pax7 paralogous genes have functionally diverged in vertebrate evolution, creating opportunity for a new distribution of roles between the two genes and the evolution of novel functions. Here we focus on the regulation and function of Pax7 in the brain and neural crest of amphibian embryos, which display a different pax7 expression pattern, compared to the other vertebrates already described. Pax7 expression is restricted to the midbrain, hindbrain and anterior spinal cord, and Pax7 activity is important for maintaining the fates of these regions, by restricting otx2 expression anteriorly. In contrast, pax3 displays broader expression along the entire neuraxis and Pax3 function is important for posterior brain patterning without acting on otx2 expression. Moreover, while both genes are essential for neural crest patterning, we show that they do so using two distinct mechanisms: Pax3 acts within the ectoderm which will be induced into neural crest, while Pax7 is essential for the inducing activity of the paraxial mesoderm towards the prospective neural crest.