Cellular differentiation

About: Cellular differentiation is a research topic. Over the lifetime, 90966 publications have been published within this topic receiving 6099252 citations. The topic is also known as: Cellular differentiation & GO:0030154.

Memory CD8+ T cells vary in differentiation phenotype in different persistent virus infections.

Abstract: The viruses HIV-1, Epstein-Barr virus (EBV), cytomegalovirus (CMV) and hepatitis C virus (HCV) are characterized by the establishment of lifelong infection in the human host, where their replication is thought to be tightly controlled by virus-specific CD8+ T cells. Here we present detailed studies of the differentiation phenotype of these cells, which can be separated into three distinct subsets based on expression of the costimulatory receptors CD28 and CD27. Whereas CD8+ T cells specific for HIV, EBV and HCV exhibit similar characteristics during primary infection, there are significant enrichments at different stages of cellular differentiation in the chronic phase of persistent infection according to the viral specificity, which suggests that distinct memory T-cell populations are established in different virus infections. These findings challenge the current definitions of memory and effector subsets in humans, and suggest that ascribing effector and memory functions to subsets with different differentiation phenotypes is no longer appropriate.

E-cadherin-mediated cell-cell adhesion prevents invasiveness of human carcinoma cells.

Abstract: The ability of carcinomas to invade and to metastasize largely depends on the degree of epithelial differentiation within the tumors, i.e., poorly differentiated being more invasive than well-differentiated carcinomas. Here we confirmed this correlation by examining various human cell lines derived from bladder, breast, lung, and pancreas carcinomas. We found that carcinoma cell lines with an epithelioid phenotype were noninvasive and expressed the epithelium-specific cell-cell adhesion molecule E-cadherin (also known as Arc-1, uvomorulin, and cell-CAM 120/80), as visualized by immunofluorescence microscopy and by Western and Northern blotting, whereas carcinoma cell lines with a fibroblastoid phenotype were invasive and had lost E-cadherin expression. Invasiveness of these latter cells could be prevented by transfection with E-cadherin cDNA and was again induced by treatment of the transfected cells with anti-E-cadherin mAbs. These findings indicate that the selective loss of E-cadherin expression can generate dedifferentiation and invasiveness of human carcinoma cells, and they suggest further that E-cadherin acts as an invasion suppressor.

Expression profiling of mammalian microRNAs uncovers a subset of brain-expressed microRNAs with possible roles in murine and human neuronal differentiation

Abstract: Background: The microRNAs (miRNAs) are an extensive class of small noncoding RNAs (18 to 25 nucleotides) with probable roles in the regulation of gene expression. In Caenorhabditis elegans, lin-4 and let-7 miRNAs control the timing of fate specification of neuronal and hypodermal cells during larval development. lin-4, let-7 and other miRNA genes are conserved in mammals, and their potential functions in mammalian development are under active study. Results: In order to identify mammalian miRNAs that might function in development, we characterized the expression of 119 previously reported miRNAs in adult organs from mouse and human using northern blot analysis. Of these, 30 miRNAs were specifically expressed or greatly enriched in a particular organ (brain, lung, liver or skeletal muscle). This suggests organ- or tissuespecific functions for miRNAs. To test if any of the 66 brain-expressed miRNAs were present in neurons, embryonal carcinoma cells were treated with all-trans-retinoic acid to promote neuronal differentiation. A total of 19 brain-expressed miRNAs (including lin-4 and let-7 orthologs) were coordinately upregulated in both human and mouse embryonal carcinoma cells during neuronal differentiation. The mammalian ortholog of C. elegans lin-28, which is downregulated by lin-4 in worms via 3' untranslated region binding, was also repressed during neuronal differentiation of mammalian embryonal carcinoma cells. Mammalian lin-28 messenger RNAs contain conserved predicted binding sites in their 3' untranslated regions for neuron-expressed miR-125b (a lin-4 ortholog), let-7a, and miR-218. Conclusions: The identification of a subset of brain-expressed miRNAs whose expression behavior is conserved in both mouse and human differentiating neurons implicates these miRNAs in mammalian neuronal development or function.

Mitogen-activated protein kinases: specific messages from ubiquitous messengers

Abstract: Signal transduction networks allow cells to perceive changes in the extracellular environment and to mount an appropriate response. Mitogen-activated protein kinase (MAPK) cascades are among the most thoroughly studied of signal transduction systems and have been shown to participate in a diverse array of cellular programs, including cell differentiation, cell movement, cell division, and cell death. A key question in studies of this cascade is, how does a ubiquitously activated regulatory enzume generate a specific and biologically appropriate cellular response? In this review we describe recent findings that provide insight into ways that the regulation, structure, and localization of MAPKs and the participation of adapters and scaffolds can help determine biological outcomes. MAPK cascades are evolutionarily conserved in all eucaryotes and play a key role in the regulation of gene expression as well as cytoplasmic activities. They typically are organized in a three-kinase architecture consisting of a MAPK, a MAPK activator (MEK, MKK, or MAPK kinase), and a MEK activator (MEK kinase [MEKK] or MAPK kinase kinase). Transmission of signals is achieved by sequential phosphorylation and activation of the components specific to a respective cascade. In the yeast Saccharomyces cerevisiae, five MAPK modules have been described; they regulate mating, filamentation, high-osmolarity responses, cell wall remodeling, and sporulation (Fig. ​(Fig.1A)1A) (reviewed in references 56 and 77). In mammalian systems five distinguishable MAPK modules have been identified so far (Fig. ​(Fig.1B).1B). These include the extracellular signal-regulated kinase 1 and 2 (ERK1/2) cascade, which preferentially regulates cell growth and differentiation, as well as the c-Jun N-terminal kinase (JNK) and p38 MAPK cascades, which function mainly in stress responses like inflammation and apoptosis (reviewed in references 57, 74, and 103). Moreover, MAPK pathways control several developmental programs, such as morphogenesis and spatial patterning in Dictyostelium amoebae (17, 45), eye development in Drosophila melanogaster (124), vulva induction in Caenorhabditis elegans (113), and T-cell development in mammals (31). FIG. 1 Schematic overview of MAPK modules. (A) In S. cerevisiae, five MAPK modules regulate mating, filamentation, high-osmolarity responses, cell wall remodeling, and sporulation. (B) Mammalian MAPK modules regulate cell growth, differentiation, stress responses, ... Individual MAPK modules generally can signal independently from each other, and this specificity is manifested in distinct physiologic responses. This is most obvious when studying MAPK signaling in S. cerevisiae. Here a particular extracellular event characteristically activates a specific MAPK module and initiates a unique cellular program (reviewed in references 56 and 77). For example, stimulation of cells with pheromone leads to the activation of the pheromone response pathway (STE11, STE7, and FUS3) (Fig. ​(Fig.2),2), which ultimately results in cell cycle arrest and the induction of mating-specific genes. However, related MAPKs whose modules share some components with the pheromone response pathway are not affected by pheromone stimulation but are activated only in response to the appropriate stimulus. For example, under conditions of high osmolarity Ste11 can lead to activation of Hog1 but does not induce mating-specific genes. Conversely, conditions that activate the filamentation pathway (which utilizes STE11 and STE7) induce only genes that regulate filamentous growth without triggering pheromone responses or responses to high osmolarity. These observations suggest that yeast cells have developed efficient mechanisms to generate pathway specificity and to successfully suppress cross talk, even when individual components participate in more than one signaling pathway. FIG. 2 Scaffold and adapter molecules in MAPK pathways. MAPK scaffolds and adapters (gray shading) are thought to promote the formation of oligomeric protein complexes with components that function in a specific MAPK module. Scaffolds have been identified in ... In metazoan cells the problem is more complex because each cell is simultaneously exposed to multiple extracellular signals and must integrate these inputs to choose an appropriate response. Thus, the biological context of a signal plays a determinative role in the way that MAPK activation is interpreted. For example, although ERKs generally regulate cell growth and cell differentiation and JNKs participate in a stress response, this is not always the case and in certain cell types activation of JNKs can induce proliferation (110). This indicates that in mammalian systems physiologic responses associated with a certain MAPK module can be cell type specific. Moreover, in PC12 cells, transient stimulation of the ERK cascade leads to proliferation whereas sustained stimulation leads to differentiation, as measured by neurite outgrowth (81). Thus, activation of the ERK cascade can lead to contrasting physiological responses in the same cellular context, suggesting that signal specificity is also determined by regulatory mechanisms other than the selective activation of a MAPK module. In this short review, we outline recent advances in understanding of this signaling system that help to explain how MAPK cascades are regulated and how specificity can be generated. Because of the power of yeast genetics, understanding of MAPK signaling in S. cerevisiae is at an advanced level, and thus many examples that utilize this organism are given. However, analogous mechanisms appear to be operative in metazoans as well. We discuss in turn the role of enzyme-substrate interactions, scaffolding proteins, subcellular targeting and localization, temporal regulation, and signal integration in determining the biological outcome of MAPK activation.