Cytoskeleton gradients in three dimensions during neurulation in the rabbit

Heterogeneity and Plasticity of Breast Cancer Stem Cells

In the last 20 years, the conventional view of breast cancer as a homogeneous collection of highly proliferating malignant cells was totally replaced by a model of increased complexity, which points out that breast carcinomas are tissues composed of multiple populations of transformed cells. A large diversity of host cells and structural components of the extracellular matrix constitute the mammary tumour microenvironment, which supports its growth and progression, where individual cancer cells evolve with cumulative phenotypic and genetic heterogeneity. Moreover, contributing to this heterogeneity, it has been demonstrated that breast cancers can exhibit a hierarchical organization composed of tumour cells displaying divergent lineage biomarkers and where, at the apex of this hierarchy, some neoplastic cells are able to self-renew and to aberrantly differentiate. Breast cancer stem cells (BCSCs), as they were entitled, not only drive tumourigenesis, but also mediate metastasis and contribute to therapy resistance.Recently, adding more complexity to the system, it has been demonstrated that BCSCs maintain high levels of plasticity, being able to change between mesenchymal-like and epithelial-like states in a process regulated by the tumour microenvironment. These stem cell state transitions play a fundamental role in the process of tumour metastasis, as well as in the resistance to putative therapeutic strategies to target these cells. In this chapter, it will be mainly discussed the emerging knowledge regarding the contribution of BCSCs to tumour heterogeneity, their plasticity, and the role that this plasticity can play in the establishment of distant metastasis. A major focus will also be given to potential clinical implications of these discoveries in breast cancer recurrence and to possible BCSC targeted therapeutics by the use of specific biomarkers.

Epithelial-to-mesenchymal transition and cancer stem cells contribute to breast cancer heterogeneity

Breast cancer is the most common cancer in women, and accounts for ~30% of new cancer cases and 15% of cancer-related deaths. Tumor relapse and metastasis are primary factors contributing to breast cancer-related deaths. Therefore, the challenge for breast cancer treatment is to sustain remission. A driving force behind tumor relapse is breast cancer heterogeneity (both intertumor, between different patients, and intratumor, within the same tumor). Understanding breast cancer heterogeneity is necessary to develop preventive interventions and targeted therapies. A recently emerging concept is that intratumor heterogeneity is driven by cancer stem cells (CSCs) that are capable of giving rise to a multitude of different cells within a tumor. Studies have highlighted linkage of CSC formation with epithelial-to-mesenchymal transition (EMT). In this review, we summarize the current understanding of breast cancer heterogeneity, links between EMT and CSCs, regulation of EMT by Runx transcription factors, and potential therapeutic strategies targeting these processes.

ZEB2 Represses the Epithelial Phenotype and Facilitates Metastasis in Ewing Sarcoma

The vast majority of cancer-related deaths are attributable to metastasis. Effective treatment of metastatic disease will be improved by a better understanding of the molecular mechanisms contributing to this phenomenon. Much of the work in this field has focused on metastasis of carcinomas, tumors of epithelial origin, while metastasis of sarcomas, tumors of mesenchymal origin, remains poorly understood. Experimental evidence from studies in carcinomas, coupled with clinical observations, highlights the importance of both epithelial and mesenchymal characteristics in these cancer cells that make them competent for metastasis. We set out to test if similar cellular plasticity contributes to sarcoma metastasis. We found that the transcription factor, ZEB2, repressed epithelial gene expression in Ewing sarcoma cells, and this, in turn, repressed the epithelial phenotype. When ZEB2 was experimentally reduced in these cells, epithelial characteristics including decreased migratory ability and cytoskeleton rearrangements were observed. Furthermore, ZEB2 reduction in Ewing sarcoma cells resulted in a decreased metastatic potential using a mouse metastasis model. Our data show that Ewing sarcoma cells may have more epithelial plasticity than previously appreciated. This coupled with previous data demonstrating Ewing sarcoma cells also have mesenchymal features primes these cells to successfully metastasize. This is clinically relevant for 2 important reasons. First, this may offer a therapeutic opportunity to induce characteristics of one cell type or the other depending on the stage of the disease. Second, and more broadly, this raises questions about the cell of origin in Ewing sarcoma and may inform future animal models of the disease.

Human embryonic stem cell differentiation on tissue engineering scaffolds: effects of NGF and retinoic acid induction

The indefinite proliferative capacity and ability to differentiate into all somatic cell types can make human embryonic stem cells (hESCs) useful in experimental and applied studies in embryonic development, tissue engineering, genetic engineering, pharmacokinetics, and the like. Cellular differentiation dynamics can be studied in monolayer cell cultures; however, it proceeds in three-dimensional (3D) organization in vivo. The aim of this study was to assess the effects of retinoic acid (RA) and nerve growth factor (NGF) on the differentiation patterns of hESCs in 3D culture environment and to compare it with the monolayer culture. Expanded hESCs (HUES-9) were differentiated in two experimental groups for 21 days: (i) two-dimensional (2D) monolayer cultures of hESC colonies, and (ii) 3D culture of hES single cells in poly(DL-lactic-co-glycolic acid) scaffolds. The media used were embryonic stem cell expansion medium (ES-EM), embryonic stem cell differentiation medium containing fetal calf serum (ES-DM), ES-EM containing either 10 ng/mL NGF or 10(-6) M RA, and their combination. Fixed specimens were analyzed with scanning electron microscopy, and expression of nestin, pan-cytokeratin, troponin, and alpha-fetoprotein at days 7, 14, and 21 was evaluated by immunohistomorphometry and reverse transcriptase--polymerase chain reaction. Results indicate different patterns of ectodermal, mesodermal, and endodermal marker expressions between groups, where NGF and RA preferentially favors the differentiation toward ectodermal and mesodermal lineages. While troponin and nestin expression is significantly elevated in 3D culture environment, pan-cytokeratin expression is favored by 2D culture instead. The effects of 3D scaffold culture imply the usefulness of testing in vitro differentiation properties of hESCs in various culture settings designed as models in prospective tissue engineering applications.

Proteomic characterization of early-stage differentiation of mouse embryonic stem cells into neural cells induced by all-trans retinoic acid in vitro

Embryonic stem (ES) cells are totipotent stem cells, which can differentiate into various kinds of cell types, including neurons. They are widely used as a model system for investigating mechanisms of differentiation events during early mouse development. In this study, proteomic techniques were used to approach the protein profile associated with the early-stage differentiation of ES cells into neuronal cells induced by all-trans retinoic acid (ATRA) in vitro. In comparison of the protein profile of parent ES cells with that of ES-derived neural-committed cells, which was induced by ATRA for four days, 24 differentially displayed protein spots were selected from two-dimensional electrophoresis (2-DE) gels for further protein identification by pepide mass fingerprinting (PMF). Nine proteins were known to being involved in the process of neural differentiation and/or neural survival. Of those, alpha-3/alpha-7 tubulin and vimentin were down-regulated, while cytokeratin 8, cytokeratin 18, G1/S-special cyclin D2, follistatin-related protein, NEL protein, platelet-activating factor acetylhydrolase IB alpha-subunit, and thioredoxin peroxidase 2 were upregulated during differentiation of ES cells to neural cells. Additionally, other 12 protein (five upregulated and seven downregulated) spots associated with ES cell differentiation into neuronal cells were not matched to known proteins so far, implicating that they might be novel proteins. The results above indicated that the molecular mechanisms of differentiation of ES cells to neural cells in vitro might be similar to those of other neural systems in vitro and identified that proteomic analysis is an effective strategy to comprehensively unravel the regulatory network of differentiation.

Targeted disruption of GAP-43 in P19 embryonal carcinoma cells inhibits neuronal differentiation. As well as acquisition of the morphological phenotype

GAP-43 is expressed in proliferating neuroblasts in vivo and in vitro, but its role during early neurogenesis has not been investigated. Here we show that neuroectodermal differentiation stimulated by retinoic acid (RA) in the embryonal carcinoma (EC) line P19 is accompanied by upregulation of GAP-43 expression in neuroepithelial precursor cells. In contrast, when upregulation of GAP-43 expression was prevented in 3 independent P19 lines because of a targeted insertion into the gene, generation of neuroepithelial precursors was inhibited. Consequently, neuronal number was significantly decreased, neuronal morphology was abnormal and fewer than 20% of all neurons were able to initiate neuritogenesis. Extracellular matrix (ECM) was unable to rescue initiation of neuritogenesis in the mutant cells, however those neurites that were extended responded normally to ECM-stimulated neurite outgrowth-promoting signals. These data suggest that GAP-43 function is required for commitment to a neuronal phenotype as well as initiation of neurite extension. However, stimulation of neurite outgrowth by ECM in P19s occurs independently of GAP-43.

The "8-kD" cytoplasmic dynein light chain is required for nuclear migration and for dynein heavy chain localization in Aspergillus nidulans

The heavy chain of cytoplasmic dynein is required for nuclear migration in Aspergillus nidulans and other fungi. Here we report on a new gene required for nuclear migration, nudG, which encodes a homologue of the "8-kD" cytoplasmic dynein light chain (CDLC). We demonstrate that the temperature sensitive nudG8 mutation inhibits nuclear migration and growth at restrictive temperature. This mutation also inhibits asexual and sexual sporulation, decreases the intracellular concentration of the nudG CDLC protein and causes the cytoplasmic dynein heavy chain to be absent from the mycelial tip, where it is normally located in wild-type mycelia. Coimmunoprecipitation experiments with antibodies against the cytoplasmic dynein heavy chain (CDHC) and the nudG CDLC demonstrated that some fraction of the cytoplasmic dynein light chain is in a protein complex with the CDHC. Sucrose gradient sedimentation analysis, however, showed that not all of the NUDG protein is complexed with the heavy chain. A double mutant carrying a cytoplasmic dynein heavy chain deletion plus a temperature-sensitive nudG mutation grew no more slowly at restrictive temperature than a strain with only the CDHC deletion. This result demonstrates that the effect of the nudG mutation on nuclear migration and growth is mediated through an interaction with the CDHC rather than with some other molecule (e.g., myosin-V) with which the 8-kD CDLC might theoretically interact.

Zebrafish vimentin: molecular characterization, assembly properties and developmental expression

To provide a basis for the investigation of the intermediate filament (IF) protein vimentin in one of the most promising experimental vertebrate systems, the zebrafish (Danio rerio), we have isolated a cDNA clone of high sequence identity to and with the characteristic features of human vimentin. Using this clone we produced recombinant zebrafish vimentin and studied its assembly behaviour. Unlike other vimentins, zebrafish vimentin formed unusually thick filaments when assembled at temperatures below 21 degrees C. At 37 degrees C few filaments were observed, which often also terminated in aggregated masses, indicating that its assembly was severely disturbed at this temperature. Between 21 and 34 degrees C apparently normal IFs were generated. By viscometry, the temperature optimum of assembly was determined to be around 28 degrees C. At this temperature, zebrafish vimentin partially rescued, in mixing experiments, the temperature-dependent assembly defect of trout vimentin. Therefore it is apparently able to "instruct" the misorganized trout vimentin such that it can enter normal IFs. This feature, that assembly is best at the normal body temperature of various species, puts more weight on the assumption that vimentin is vital for some aspects of generating functional adult tissues. Remarkably, like in most other vertebrates, zebrafish vimentin appears to be an abundant factor in the lens and the retina as well as transiently, during development, in various parts of the central and peripheral nervous system. Therefore, promising cell biological investigations may now be performed with cells involved in the generation of the vertebrate eye and brain, and, in particular, the retina. Moreover, the power of genetics of the zebrafish system may be employed to investigate functional properties of vimentin in vivo.

A simple molecular model of neurulation

A molecular model for the morphogenesis of the central nervous system is built and solved by computer. The formalism rests on molecular-biological data gathered from insects and vertebrates during neural differentiation and neuronal fate specification. Two genetic, hierarchically organized switches are introduced, one associated with f1p4al tissue formation, and the other with neuronal specification. The model switches evolve in time, setting up very similar "prepatterns" of genetic activity in both insects and vertebrates, as observed experimentally. We introduce the hypothesis that cell adhesion and motion are regulated by the switches. If cell motion is turned on by the neural switch, the whole neural tissue (neural plate) thickens, buckles, and folds, ultimately creating a closed neural tube (primary neurulation). When mitoses are more frequent in neural plate tissue, ingression of a neural cell mass takes place instead (secondary neurulation). If cell motions are controlled by the neuronal switch, rather than by the neural one, the differentiation of isolated neuroblasts is observed, which delaminate individually (as in insect neural cord formation). The model thus displays the three major known patterns of neurogenesis; the transition between the vertebrate and insect cases is predicted to result from changes in genetic regulation downstream of the switch genes, and affecting cell adhesion and motility properties. Little is known experimentally about the concerned pathways: their importance as a fruitful area for future investigation is emphasized by our theoretical results.