The lack of reliable molecular markers for normal differentiated epithelial cells limits understanding of human gastric carcinogenesis. Recognized precursor lesions for gastric adenocarcinoma are intestinal metaplasia and spasmolytic polypeptide expressing metaplasia (SPEM), defined here by ectopic CDX2 and TFF2 expression, respectively. In mice, expression of the bHLH transcription factor MIST1, normally restricted to mature chief cells, is down-regulated as chief cells undergo experimentally induced metaplasia. Here, we show MIST1 expression is also a specific marker of human chief cells. The mainstays of therapy in gastric carcinoma are early recognition, resection, and neoadjuvant or adjuvant therapy. However, gastric cancer remains the second largest cause of cancer-related mortality worldwide, 1 which drastically illustrates our lack of understanding of the sequence and progression of preneoplastic conditions. The traditional linear progression model of cellular changes, such as (Helicobacter-mediated) inflammation, atrophy, intestinal metaplasia (IM), dysplasia, and carcinoma, 2-4 does not apply to all cases and does not allow incorporation of more recently recognized entities. For example, there are distinct types of IMs, not all carrying definitive preneoplastic potential, and some authors have argued that IM in general is a paraneoplastic condition because the earliest gastric carcinomas arise from gasSupported by

SUMMARYEstablishment of specific characteristics of each embryonic cardiac chamber is crucial for development of a fully functional adult heart. Despite the importance of defining and maintaining unique features in ventricular and atrial cardiomyocytes, the regulatory mechanisms guiding these processes are poorly understood. Here, we show that the homeodomain transcription factors Nkx2.5 and Nkx2.7 are necessary to sustain ventricular chamber attributes through repression of atrial chamber identity. Mutation of nkx2.5 in zebrafish yields embryos with diminutive ventricular and bulbous atrial chambers. These chamber deformities emerge gradually during development, with a severe collapse in the number of ventricular cardiomyocytes and an accumulation of excess atrial cardiomyocytes as the heart matures. Removal of nkx2.7 function from nkx2.5 mutants exacerbates the loss of ventricular cells and the gain of atrial cells. Moreover, in these Nkx-deficient embryos, expression of vmhc, a ventricular gene, fades, whereas expression of amhc, an atrial gene, expands. Cell-labeling experiments suggest that ventricular cardiomyocytes can transform into atrial cardiomyocytes in the absence of Nkx gene function. Through suggestion of transdifferentiation from ventricular to atrial fate, our data reveal a pivotal role for Nkx genes in maintaining ventricular identity and highlight remarkable plasticity in differentiated myocardium. Thus, our results are relevant to the etiologies of fetal and neonatal cardiac pathology and could direct future innovations in cardiac regenerative medicine.

Morphogen gradients expose cells to different signal concentrations and induce target genes with different ranges of expression. To determine how the Nodal morphogen gradient induces distinct gene expression patterns during zebrafish embryogenesis, we measured the activation dynamics of the signal transducer Smad2 and the expression kinetics of long- and short-range target genes. We found that threshold models based on ligand concentration are insufficient to predict the response of target genes. Instead, morphogen interpretation is shaped by the kinetics of target gene induction: the higher the rate of transcription and the earlier the onset of induction, the greater the spatial range of expression. Thus, the timing and magnitude of target gene expression can be used to modulate the range of expression and diversify the response to morphogen gradients.DOI: http://dx.doi.org/10.7554/eLife.05042.001

Cancer-associated fibroblasts (CAF) are key contributors to malignant progression, but their critical regulators remain largely unknown. In this study, we examined the role of Twist1, a central regulator of epithelial–mesenchymal transition in carcinoma cells, in the transdifferentiation of normal quiescent fibroblasts to CAF and we defined its upstream controls and downstream effectors. Primary human gastric fibroblast and CAF cultures were established from gastrectomy specimens and validated as nontumor cells by somatic mutation analyses. In these cultures, exposure to the proinflammatory cytokine IL6 commonly expressed in tumors was sufficient to induce Twist1 expression in normal fibroblasts and transdifferentiate them into CAFs via STAT3 phosphorylation. In xenograft models, tumor infiltration of Twist1-expressing CAFs was enhanced strongly by ectopic IL6 expression in gastric or breast cancer cells. We found that Twist1 expression was necessary and sufficient for CAF transdifferentiation. Enforced expression of Twist1 in normal fibroblasts was also sufficient to drive CAF marker expression and malignant character in gastric cancer cells both in vitro and in vivo. Conversely, silencing the expression of Twist1 in CAFs abrogated their tumor-promoting properties. Downstream of Twist1, we defined the chemokine CXCL12 as a transcriptional target. Clinically, CXCL12 and Twist1 expression were correlated in CAFs present in gastric tumor specimens. Finally, ectopic expression of Twist1 in normal fibroblasts suppressed premature senescence, whereas Twist1 attenuation accelerated senescence in CAFs. Our findings define Twist1 as a compelling target to deprogram the tumor-supporting features of the cancer microenvironment. Cancer Res; 75(1); 73–85. ©2014 AACR.