Subcellular localization of Mitf in monocytic cells

Microphthalmia-associated transcription factor (Mitf) is a transcription factor that plays an important role in regulating the development of several cell lineages. The subcellular localization of Mitf is dynamic and is associated with its transcription activity. In this study, we examined factors that affect its subcellular localization in cells derived from the monocytic lineage since Mitf is present abundantly in these cells. We identified a domain encoded by Mitf exon 1B1b to be important for Mitf to commute between the cytoplasm and the nucleus. Deletion of this domain disrupts the shuttling of Mitf to the cytoplasm and results in its retention in the nucleus. M-CSF and RANKL both induce nuclear translocation of Mitf. We showed that Mitf nuclear transport is greatly influenced by ratio of M-CSF/Mitf protein expression. In addition, cell attachment to a solid surface also is needed for the nuclear transport of Mitf

Down-Regulation of DNA Mismatch Repair Enhances Initiation and Growth of Neuroblastoma and Brain Tumour Multicellular Spheroids

Multicellular tumour spheroid (MCTS) cultures are excellent model systems for simulating the development and microenvironmental conditions of in vivo tumour growth. Many documented cell lines can generate differentiated MCTS when cultured in suspension or in a non-adhesive environment. While physiological and biochemical properties of MCTS have been extensively characterized, insight into the events and conditions responsible for initiation of these structures is lacking. MCTS are formed by only a small subpopulation of cells during surface-associated growth but the processes responsible for this differentiation are poorly understood and have not been previously studied experimentally. Analysis of gene expression within spheroids has provided clues but to date it is not known if the observed differences are a cause or consequence of MCTS growth. One mechanism linked to tumourigenesis in a number of cancers is genetic instability arising from impaired DNA mismatch repair (MMR). This study aimed to determine the role of MMR in MCTS initiation and development. Using surface-associated N2a and CHLA-02-ATRT culture systems we have investigated the impact of impaired MMR on MCTS growth. Analysis of the DNA MMR genes MLH1 and PMS2 revealed both to be significantly down-regulated at the mRNA level compared with non-spheroid-forming cells. By using small interfering RNA (siRNA) against these genes we show that silencing of MLH1 and PMS2 enhances both MCTS initiation and subsequent expansion. This effect was prolonged over several passages following siRNA transfection. Down-regulation of DNA MMR can contribute to tumour initiation and progression in N2a and CHLA-02-ATRT MCTS models. Studies of surface-associated MCTS differentiation may have broader applications in studying events in the initiation of cancer foci

Contribution of human hematopoietic stem cells to liver repair

Immune-deficient mouse models of liver damage allow examination of human stem cell migration to sites of damage and subsequent contribution to repair and survival. In our studies, in the absence of a selective advantage, transplanted human stem cells from adult sources did not robustly become hepatocytes, although some level of fusion or hepatic differentiation was documented. However, injected stem cells did home to the injured liver tissue and release paracrine factors that hastened endogenous repair and enhanced survival. There were significantly higher levels of survival in mice with a toxic liver insult that had been transplanted with human stem cells but not in those transplanted with committed progenitors. Transplantation of autologous adult stem cells without conditioning is a relatively safe therapy. Adult stem cells are known to secrete bioactive factors that suppress the local immune system, inhibit fibrosis (scar formation) and apoptosis, enhance angiogenesis, and stimulate recruitment, retention, mitosis, and differentiation of tissue-residing stem cells. These paracrine effects are distinct from the direct differentiation of stem cells to repair tissue. In patients at high risk while waiting for a liver transplant, autologous stem cell therapy could be considered, as it could delay the decline in liver function

Following damage, the majority of bone marrow-derived airway cells express an epithelial marker

<p>Abstract</p> <p>Background</p> <p>Adult-derived bone marrow stem cells are capable of reconstituting the haematopoietic system. However there is ongoing debate in the literature as to whether bone marrow derived cells have the ability to populate other tissues and express tissue specific markers. The airway has been an organ of major interest and was one of the first where this was demonstrated. We have previously demonstrated that the mouse airway can be repopulated by side population bone marrow transplanted cells. Here we investigate the frequency and phenotypic nature of these bone marrow derived cells.</p> <p>Methods</p> <p>Female mice were engrafted with male whole bone marrow or side population (SP) cells and subjected to detergent-induced damage after 3 months. Donor cells were identified by Y chromosome fluorescence in situ hybridisation and their phenotype was assessed by immunohistochemistry on the same sections. Slides were visualised by a combination of widefield and deconvolved microscopy and whole cells were analysed on cytospin preparations.</p> <p>Results</p> <p>The frequencies of engraftment of male cells in the airway of mice that show this (9/10), range from 1.0 – 1.6% with whole marrow and 0.6 – 1.5% with SP cells. Undamaged controls have only between 0.1 and 0.2% male cells in the trachea. By widefield microscopy analysis we find 60.2% (53/88) of male donor derived cells express cytokeratins as a marker of epithelial cells. These results were reinforced using deconvolved microscopy and scored by two independent investigators. In addition cytospin analysis of cells dissociated from the damaged trachea of engrafted mice also reveals donor derived Y chromosome positive cells that are immunopositive for cytokeratin. Using cytokeratin and the universal haematopoietic marker CD45 immunohistochemistry, we find the donor derived cells fall into four phenotypic classes. We do not detect cytokeratin positive cells in whole bone marrow using cytokeratin immunostaining and we do not detect any cytokeratin mRNA in SP or bone marrow samples by RT-PCR.</p> <p>Conclusion</p> <p>The appearance of bone marrow derived cells in the tracheal epithelium is enriched by detergent-induced tissue damage and the majority of these cells express an epithelial marker. The cytokeratin positive donor derived cells in the tracheal epithelium are not present in the injected donor cells and must have acquired this novel phenotype <it>in vivo</it>.</p

A Mismatch-Based Model for Memory Reconsolidation and Extinction in Attractor Networks

The processes of memory reconsolidation and extinction have received increasing attention in recent experimental research, as their potential clinical applications begin to be uncovered. A number of studies suggest that amnestic drugs injected after reexposure to a learning context can disrupt either of the two processes, depending on the behavioral protocol employed. Hypothesizing that reconsolidation represents updating of a memory trace in the hippocampus, while extinction represents formation of a new trace, we have built a neural network model in which either simple retrieval, reconsolidation or extinction of a stored attractor can occur upon contextual reexposure, depending on the similarity between the representations of the original learning and reexposure sessions. This is achieved by assuming that independent mechanisms mediate Hebbian-like synaptic strengthening and mismatch-driven labilization of synaptic changes, with protein synthesis inhibition preferentially affecting the former. Our framework provides a unified mechanistic explanation for experimental data showing (a) the effect of reexposure duration on the occurrence of reconsolidation or extinction and (b) the requirement of memory updating during reexposure to drive reconsolidation