Chromosomal abnormalities and tumor development: from genes to therapeutic mechanisms

This article highlights the recent advances in our understanding of the molecular structure and function of proteins that are activated or created by chromosomal abnormalities and discusses their possible role in tumor development. The molecular characterization of these proteins has revealed that tumor-specific fusion proteins are the consequence of the majority of chromosomal translocations associated with leukemias and solid tumors. A common theme that emerges is that creation of these proteins disrupts the normal development of tumor-specific target cells by blocking apoptosis. These insights identify these chromosomal translocation-associated genes as potential targets for improved cancer therapies. BioEssays 20:922–930, 1998. © 1998 John Wiley & Sons, Inc.     

Polycomb repressive complex 1: Regulators of neurogenesis from embryonic to adult stage

Development of vertebrate nervous system is a complex process which involves differential gene expression and disruptions in this process or in the mature brain, may lead to neurological disorders and diseases. Extensive work that spanned several decades using rodent models and recent work on stem cells have helped uncover the intricate process of neuronal differentiation and maturation. There are various morphological changes, genetic and epigenetic modifications which occur during normal mammalian neural development, one of the chromatin modifications that controls vital gene expression are the posttranslational modifications on histone proteins, that controls accessibility of translational machinery. Among the histone modifiers, polycomb group proteins (PcGs), such as Ezh2, Eed and Suz12 form large protein complexes—polycomb repressive complex 2 (PRC2); while Ring1b and Bmi1 proteins form core of PRC1 along with accessory proteins such as Cbx, Hph, Rybp and Pcgfs catalyse histone modifications such as H3K27me3 and H2AK119ub1. PRC1 proteins are known to play critical role in X chromosome inactivation in females but they also repress the expression of key developmental genes and tightly regulate the mammalian neuronal development. In this review we have discussed the signalling pathways, morphogens and nuclear factors that initiate, regulate and maintain cells of the nervous system. Further, we have extensively reviewed the recent literature on the role of Ring1b and Bmi1 in mammalian neuronal development and differentiation; as well as highlighted questions that are still unanswered.     

Two transitions of haemoglobin expression in Xenopus: from embryonic to larval and from larval to adult

Electrophoretic analyses of haemoglobin and globin phenotypes in families of Xenopus borealis and Xenopus l. laevis revealed two developmental haemoglobin transitions during ontogeny. The first transition occurs at the developmental stage when tadpoles begin to feed. It is characterized by the decline of embryonic-specific globins in favour of novel, tadpole-specific globins (X. borealis) correlated to changes in the haemoglobin pattern. We suppose that this switch results from the replacement of a primitive, ventral blood island-dependent erythrocyte population by tadpole erythrocytes from other erythropoietic sites. Several other globin chains and haemoglobins are present in both young tadpoles and throughout larval life. The second, well-known transition occurs during metamorphosis, where all tadpole haemoglobins are replaced by adult haemoglobins composed of entirely different globin chains.     

Developmental mechanisms and adult stem cells for therapeutic lung regeneration

Chronic degenerative lung diseases are essentially untreatable pathological conditions. By contrast, the healthy lung has numerous mechanisms that allow for rapid repair and restoration of function following minor acute injuries. We discuss the normal endogenous processes of lung development, homeostatic maintenance and repair and consider the research strategies required for the development of methods for human therapeutic lung regeneration.     

Mitochondrial quality control in diabetic cardiomyopathy: from molecular mechanisms to therapeutic strategies

In diabetic cardiomyopathy (DCM), a major diabetic complication, the myocardium is structurally and functionally altered without evidence of coronary artery disease, hypertension or valvular disease. Although numerous anti-diabetic drugs have been applied clinically, specific medicines to prevent DCM progression are unavailable, so the prognosis of DCM remains poor. Mitochondrial ATP production maintains the energetic requirements of cardiomyocytes, whereas mitochondrial dysfunction can induce or aggravate DCM by promoting oxidative stress, dysregulated calcium homeostasis, metabolic reprogramming, abnormal intracellular signaling and mitochondrial apoptosis in cardiomyocytes. In response to mitochondrial dysfunction, the mitochondrial quality control (MQC) system (including mitochondrial fission, fusion, and mitophagy) is activated to repair damaged mitochondria. Physiological mitochondrial fission fragments the network to isolate damaged mitochondria. Mitophagy then allows dysfunctional mitochondria to be engulfed by autophagosomes and degraded in lysosomes. However, abnormal MQC results in excessive mitochondrial fission, impaired mitochondrial fusion and delayed mitophagy, causing fragmented mitochondria to accumulate in cardiomyocytes. In this review, we summarize the molecular mechanisms of MQC and discuss how pathological MQC contributes to DCM development. We then present promising therapeutic approaches to improve MQC and prevent DCM progression.     

Modeling human neurodevelopmental disorders in the Xenopus tadpole: from mechanisms to therapeutic targets

The Xenopus tadpole model offers many advantages for studying the molecular, cellular and network mechanisms underlying neurodevelopmental disorders. Essentially every stage of normal neural circuit development, from axon outgrowth and guidance to activity-dependent homeostasis and refinement, has been studied in the frog tadpole, making it an ideal model to determine what happens when any of these stages are compromised. Recently, the tadpole model has been used to explore the mechanisms of epilepsy and autism, and there is mounting evidence to suggest that diseases of the nervous system involve deficits in the most fundamental aspects of nervous system function and development. In this Review, we provide an update on how tadpole models are being used to study three distinct types of neurodevelopmental disorders: diseases caused by exposure to environmental toxicants, epilepsy and seizure disorders, and autism.     

Cardiomyocyte differentiation from embryonic and adult stem cells

In recent years multiple reports indicating that embryonic as well as adult stem cells can differentiate to cardiomyocytes have ignited discussions on whether these stem cells could lead to new therapies for patients with heart disease. Recent developments have been made in the generation of cardiomyocytes from both embryonic and adult stem cells, and progress towards clinical applications in patients with heart failure has been made. Nevertheless, controversies surrounding safety and transdifferentiation issues will need to be overcome before these stem cell approaches can reach their full potential.     

Conversion of embryonic form to adult forms of N-CAM in vitro: results from de novo synthesis of adult forms

During normal development, the neural cell adhesion molecule N-CAM changes at the cell-surface from a sialic acid-rich embryonic, or E form, to several adult, or A forms that have less sialic acid (E-to-A conversion). To investigate the cellular and molecular mechanisms that underlie these changes, we have established conditions under which E-to-A conversion occurs in cultured explants of central nervous system tissues. Mouse cerebellum, chick spinal cord, and chick retina that express the E form of N-CAM were dissected and cultured on collagen gels. After 3-6 d in culture, increased proportions of A forms were synthesized, as revealed by specific immunoprecipitation and immunoblotting. The rate of E-to-A conversion and the proportions of the different A forms synthesized in vitro were similar to those observed for the tissues in vivo at comparable times. In addition, the explants incorporated radioactive precursors of amino sugars into N-CAM, and the electrophoretic mobilities of the E and A forms of N-CAM were altered by treatment with neuraminidase in a way comparable to that found for N-CAM obtained directly from tissue. These results suggest that the post translational processing in vitro was similar to that in vivo. Logistic studies on cell division and death in the explants suggested that E-to-A conversion resulted mainly from a specific increase in synthesis of A forms in individual cells rather than as a consequence of differential birth or death within distinct cell populations. The data were consistent with the possibility that the increase in synthesis of A forms occurred either in cells that had previously synthesized E forms or in a distinct population of cells that already synthesized A forms. Cells dissociated from embryonic central nervous system tissues and cultured in vitro were also found to undergo E-to-A conversion at the same rate as the explant cultures, which suggests that if intercellular signals were responsible for initiation of the change in synthetic pattern, they had already occurred in vivo before the time of culture. In pulse-chase experiments, the E form of N-CAM that was synthesized during the first day after explantation persisted as E form for several days, at times when newly synthesized N-CAM was predominantly in A forms. These results indicate that in cultured neural tissue, the E form of N-CAM is not processed into A forms but is gradually degraded and replaced by newly synthesized A forms.(ABSTRACT TRUNCATED AT 400 WORDS)     

Cell death regulation by MAMs: from molecular mechanisms to therapeutic implications in cardiovascular diseases

The endoplasmic reticulum (ER) and mitochondria are interconnected intracellular organelles with vital roles in the regulation of cell signaling and function. While the ER participates in a number of biological processes including lipid biosynthesis, Ca²⁺ storage and protein folding and processing, mitochondria are highly dynamic organelles governing ATP synthesis, free radical production, innate immunity and apoptosis. Interplay between the ER and mitochondria plays a crucial role in regulating energy metabolism and cell fate control under stress. The mitochondria-associated membranes (MAMs) denote physical contact sites between ER and mitochondria that mediate bidirectional communications between the two organelles. Although Ca²⁺ transport from ER to mitochondria is vital for mitochondrial homeostasis and energy metabolism, unrestrained Ca²⁺ transfer may result in mitochondrial Ca²⁺ overload, mitochondrial damage and cell death. Here we summarize the roles of MAMs in cell physiology and its impact in pathological conditions with a focus on cardiovascular disease. The possibility of manipulating ER-mitochondria contacts as potential therapeutic approaches is also discussed.Subject terms: Cardiovascular diseases, Cardiomyopathies     

Keratinocytes derived from embryonic stem cells induce wound healing in mice

The skin plays an important role in defending the body against the environment. Treatments for burns and skin injuries that use autologous or allogenic skin grafts derived from adult or embryonic stem cells are promising. Embryonic stem cells are candidates for regenerative and reparative medicine. We investigated the utility of keratinocyte-like cells, which are differentiated from mouse embryonic stem cells, for wound healing using a mouse surgical wound model. Mice were allocated to the following groups: experimental, in which dressing and differentiated cells were applied after the surgical wound was created; control, in which only the surgical wound was created; sham, in which only the dressing was applied after the surgical wound was created; and untreated animal controls with healthy skin. Biopsies were taken from each group on days 3, 5 and 7 after cell transfer. Samples were fixed in formalin, then stained with Masson’s trichrome and primary antibodies to interleukin-8 (IL-8), fibroblast growth factor-2 (FGF-2), monocyte chemoattractant protein-1 (MCP-1), collagen-1 and epidermal growth factor (EGF) using the indirect immunoperoxidase technique for light microscopy. Wound healing was faster in the experimental group compared to the sham and control groups. The experimental group exhibited increased expression of IL-8, FGF-2 and MCP-1 during early stages of wound healing (inflammation) and collagen-1 and EGF expression during late stages of wound healing (proliferation and remodeling). Keratinocytes derived from embryonic stem cells improved wound healing and influenced the wound healing stages.     

Persistent adult zebrafish behavioral deficits results from acute embryonic exposure to gold nanoparticles

As the number of products containing nanomaterials increase, human exposure to nanoparticles (NPs) is unavoidable. Presently, few studies focus on the potential long-term consequences of developmental NP exposure. In this study, zebrafish embryos were acutely exposed to three gold NPs that possess functional groups with differing surface charge. Embryos were exposed to 50 μg/mL of 1.5 nm gold nanoparticles (AuNPs) possessing negatively charged 2-mercaptoethanesulfonic acid (MES) or neutral 2-(2-(2-mercaptoethoxy)ethoxy)ethanol (MEEE) ligands or 10 μg/mL of the AuNPs possessing positively charged trimethylammoniumethanethiol (TMAT). Both MES- and TMAT-AuNP exposed embryos exhibited hypo-locomotor activity, while those exposed to MEEE-AuNPs did not. A subset of embryos that were exposed to 1.5 nm MES- and TMAT-AuNPs during development from 6 to 120 h post fertilization was raised to adulthood. Behavioral abnormalities and the number of survivors into adulthood were evaluated at 122 days post fertilization. We found that both treatments induced abnormal startle behavior following a tap stimulus. However, the MES-AuNPs exposed group also exhibited abnormal adult behavior in the light and had a lower survivorship into adulthood. This study demonstrates that acute, developmental exposure to 1.5 nm MES- and TMAT-AuNPs, two NPs differing only in the functional group, affects larval behavior, with behavioral effects persisting into adulthood.     

Cloning of total mRNA populations from adult and embryonic mice

Total clone banks of cDNAs synthesized from poly(A)-RNA obtained from three stages of the developing mouse were constructed. The stages chosen were 13-day-old embryo, neonatal, and fully grown adult. To have as complete a bank as possible, large numbers of individual clones were generated ~400,000 for the 13th day embryo and neonatal mouse and ~610,000 for the adult bank. In each case the clone bank was constructed by inserting double stranded cDNA into the PstI site of pBR322 by the “G-C tailing” method. Sequences cloned in this way could be separated from the plasmid host DNA by treatment of the resultant total chimeric plasmid population with PstI. Aliquots of the cloned cDNA material were labeled with ³²P by “nick translation” using Escherichia coli DNA polymerase I for the preparation of hybridization probes. Back-hybridization of these probes to the total clone banks allowed the determination of the sequence diversity among the above three very different developmental stages. The use of such clone banks should allow the identification of developmental stage specific mRNAs.     

Correction to: Mitochondrial dynamics regulators: implications for therapeutic intervention in cancer

Cell Biology and Toxicology -     

Induction of melanocytes from embryonic stem cells and their therapeutic potential

Embryonic stem (ES) cells from many organisms have the capacity to generate in vitro a wide variety of cell types depending on their environment. Understanding precisely how such toti- or pluripotent cells may be driven towards a specific lineage represents a major challenge if our ambition of using ES cells to generate a ready supply of healthy cells for cell-based therapies for a range of diseases is to be realized. Recent advances have demonstrated that melanocytes and retinal pigmented epithelial (RPE) cells exhibiting the characteristics of their natural counterparts can be induced from undifferentiated ES cells grown on monolayers of specific stromal cell lines or by using a combination of Wnt3a, Endothelin-3 and SCF. The ability to induce pigment cells from ES cells promises to facilitate our understanding of the precise molecular mechanisms underlying this process and moreover enable us to distinguish the program of gene expression that underpins the choice made between generating a nerual crest-type melanocyte versus an RPE cell. Moreover, once the combination of signals required to induce a particular type of pigment cell are characterized, the way may be open for future cell-based therapy for various diseases caused by defective pigment cells.