New insights into fish ion regulation and mitochondrion-rich cells

Compared to terrestrial animals, fish have to cope with more-challenging osmotic and ionic gradients from aquatic environments with diverse salinities, ion compositions, and pH values. Gills, a unique and highly studied organ in research on fish osmoregulation and ionoregulation, provide an excellent model to study the regulatory mechanisms of ion transport. The present review introduces and discusses some recent advances in relevant issues of teleost gill ion transport and functions of gill ionocytes. Based on accumulating evidence, a conclusive model of NaCl secretion in gills of euryhaline teleosts has been established. Interpretations of results of studies on freshwater fish gill Na+/Cl- uptake mechanisms are still being debated compared with those for NaCl secretion. Current models for Na+/Cl- uptake are proposed based on studies in traditionally used model species. Many reported inconsistencies are claimed to be due to differences among species, various experimental designs, or acclimation conditions. Having the benefit of advanced techniques in molecular/cellular biology, functional genomics, and model animals, several new notions have recently been raised concerning relevant issues of Na+/Cl- uptake pathways. Several new windows have been opened particularly in terms of molecular mechanisms of ionocyte differentiation and energy metabolite transport between gill cells during environmental challenge.     

New insights into the regulation of human megakaryocytopoiesis

It is apparent that multiple cellular stages and biologic processes can be identified during megakaryocytopoiesis that are potentially subject to control by hematopoietic growth factors and marrow accessory cell populations. Two classes of megakaryocyte progenitor cells, the colony forming unit-megakaryocyte (CFU-MK) and the burst forming unit-megakaryocyte (BFU-MK), have now been detected in normal human bone marrow cells. The BFU-MK by virtue of the greater cellular content of its resultant colonies and the delayed time of appearance of these colonies appears to be a more primitive progenitor cell with a greater proliferative potential than the CFU-MK. A number of hematopoietic growth factors including megakaryocyte colony stimulating factor, (MK-CSF), recombinant erythropoietin (EPO) and granulocyte macrophage colony stimulating factor (GM-CSF) are each capable of increasing cloning efficiency of human megakaryocyte progenitor cells. It is presently unknown whether these factors act directly on the CFU-MK or whether they stimulate marrow accessory cells to elaborate growth factors that influence CFU-MK proliferation. In order to answer this question, the effect of these growth factors on the cloning efficiency of a human megakaryocytic cell line, EST-IU, was examined. Each of these factors was capable of increasing leukemia cell colony formation. One can conclude from these studies that MK-CSF, EPO, and GM-CSF act directly on cells of the megakaryocytic lineage. The physiologic significance of the lineage nonspecific effects of EPO and GM-CSF on megakaryocytopoiesis is yet to be determined. On the basis of these observations, a model of human megakaryocytopoiesis was suggested. Several factors appear able to influence multiple steps in megakaryocytic development, whereas others influence only specific stages or cellular events occurring during megakaryocytopoiesis.     

New insights into Raf regulation from structural analyses

BRAF is a highly regulated protein kinase that controls cell fate in animal cells. Recent structural analyses have revealed how active and inactive forms of BRAF bind to dimers of the scaffold protein 14-3-3. Inactive BRAF binds to 14-3-3 as a monomer and is held in an inactive conformation by interactions with ATP and the substrate kinase MEK, a striking example of enzyme inhibition by substrate binding. A change in the phosphorylation state of BRAF shifts the stoichiometry of the BRAF:14-3-3 complex from 1:2 to 2:2, resulting in stabilization of the active dimeric form of the kinase. These new findings uncover unexpected features of the regulatory mechanisms underlying Raf biology and help explain the paradoxical activation of Raf by small-molecule inhibitors.     

New insights into the dynamic regulation of water and acid-base balance by renal epithelial cells

Maintaining tight control over body fluid and acid-base homeostasis is essential for human health and is a major function of the kidney. The collecting duct is a mosaic of two cell populations that are highly specialized to perform these two distinct processes. The antidiuretic hormone vasopressin (VP) and its receptor, the V2R, play a central role in regulating the urinary concentrating mechanism by stimulating accumulation of the aquaporin 2 (AQP2) water channel in the apical membrane of collecting duct principal cells. This increases epithelial water permeability and allows osmotic water reabsorption to occur. An understanding of the basic cell biology/physiology of AQP2 regulation and trafficking has informed the development of new potential treatments for diseases such as nephrogenic diabetes insipidus, in which the VP/V2R/AQP2 signaling axis is defective. Tubule acidification due to the activation of intercalated cells is also critical to organ function, and defects lead to several pathological conditions in humans. Therefore, it is important to understand how these "professional" proton-secreting cells respond to environmental and cellular cues. Using epididymal proton-secreting cells as a model system, we identified the soluble adenylate cyclase (sAC) as a sensor that detects luminal bicarbonate and activates the vacuolar proton-pumping ATPase (V-ATPase) via cAMP to regulate tubular pH. Renal intercalated cells also express sAC and respond to cAMP by increasing proton secretion, supporting the hypothesis that sAC could function as a luminal sensor in renal tubules to regulate acid-base balance. This review summarizes recent advances in our understanding of these fundamental processes.     

New insights into the evolutionary history of photoreceptor cells

Although the common descent of all life has been widely accepted since Darwin's time, new research occasionally provides us with arresting reminders of the unity of evolutionary history. Recent papers by Arendt et al. and Panda et al. provide one such reminder. They illustrate that the two classes of animal photoreceptors, ciliary and rhabdomeric photoreceptors, are likely to share an ancient common ancestor and have been evolving in parallel since their duplication over 600 million years ago.     

New insights into pancreatic cancer stem cells

Pancreatic cancer(PC) has been one of the deadliest of all cancers, with almost uniform lethality despite aggressive treatment. Recently, there have been important advances in the molecular, pathological and biological understandingof pancreatic cancer. Even after the emergence of recent new targeted agents and the use of multiple therapeutic combinations, no treatment option is viable in patients with advanced cancer. Developing novel strategies to target progression of PC is of intense interest. A small population of pancreatic cancer stem cells(CSCs) has been found to be resistant to chemotherapy and radiation therapy. CSCs are believed to be responsible for tumor initiation, progression and metastasis. The CSC research has recently achieved much progress in a variety of solid tumors, including pancreatic cancer to some extent. This leads to focus on understanding the role of pancreatic CSCs. The focus on CSCs may offer new targets for prevention and treatment of this deadly cancer. We review the most salient developments in important areas of pancreatic CSCs. Here, we provide a review of current updates and new insights on the role of CSCs in pancreatic tumor progression with special emphasis on Dcl K1 and Lgr5, signaling pathways altered by CSCs, and the role of CSCs in prevention and treatment of PC.     

New insights into the regulation of phytochelatin biosynthesis in A. thaliana cells from metabolite profiling analyses

In higher plants and some fungi, heavy metals induce the synthesis of chelating peptides known as phytochelatins (PCs). They are characterized by the general structure (gamma-Glu-Cys)n-Gly, but in some plant species, the C-terminal glycine can be replaced by serine, glutamine, glutamate or alanine, leading to iso-phytochelatins (iso-PCs). Although the distribution of iso-PCs is considered to differ from one species to another, we previously showed that Arabidopsis thaliana (A. thaliana) cells are able to synthesize most PC-related peptides (PCs and iso-PCs) described in the literature. We also observed an accumulation of the dipeptide gamma-glutamylcysteine (gamma-EC) when cadmium (Cd) (200 microM) was added to the culture medium, suggesting that either glutathione synthetase or glycine availability could be a limiting factor for the biosynthesis of PC-related peptides. In this context, the aim of the present work was to seek new insights into the regulation of PC synthesis by performing metabolic profiling using liquid chromatography-mass spectrometry. The levels of PC-related peptides and their precursors were measured in A. thaliana cells following Cd exposure. A range of doses (0, 50, 200 and 400 microM CdNO3) and kinetic studies (from 1 to 48 h) showed a dose threshold (50 microM CdNO3) and a lag time between the appearance of PCs and iso-PCs concomitant with the gamma-EC accumulation induced by Cd, occurring at cadmium concentrations above 50 microM. This accumulation was suppressed by supplementation of the culture medium with 25 mM glycine. Glycine supplementation had a limited impact on the concentrations of glutathione and PCs whereas the levels of most iso-PCs were significantly increased. Taken together, these results indicate that GSH is involved in the biosynthesis of the iso-PCs in vivo, and that the biosynthesis of PC-related peptides is limited by the availability of glycine in the presence of high cadmium concentrations.     

New insights into the genetic regulation of homologue disjunction in mammalian oocytes

Mammalian oocytes execute a unique meiotic programme involving 2 arrest stages and an unusually protracted preamble to chromosome segregation during the first meiotic division (meiosis I). How mammalian oocytes successfully navigate their exceptional meiotic journey has long been a question of immense interest. Understanding the minutiae of female mammalian meiosis I is not merely of academic interest as 80-90% of human aneuploidy is the consequence of errors arising at this particular stage of oocyte maturation, a stage with a peculiar vulnerability to aging. Recent evidence indicates that oocytes employ many of the same cast of proteins during meiosis I as somatic cells do during mitosis, often to execute similar tasks, but intriguingly, occasionally delegate them to unexpected and unprecedented roles. This is epitomised by the master cell-cycle regulon, the anaphase-promoting complex or cyclosome (APC/C), acting in concert with a critical APC/C-targeted surveillance mechanism, the spindle assembly checkpoint (SAC). Together, the APC/C and the SAC are among the most influential entities overseeing the fidelity of cell-cycle progression and the precision of chromosome segregation. Here I review the current status of pivotal elements underpinning homologue disjunction in mammalian oocytes including spindle assembly, critical biochemical anaphase-initiating events, APC/C activity and SAC signalling along with contemporary findings relevant to progressive oocyte SAC dysfunction as a model for age-related human aneuploidy.     

New insights into Legionella pneumophila biofilm regulation by c-di-GMP signaling

The waterborne pathogen Legionella pneumophila grows as a biofilm, freely or inside amoebae. Cyclic-di-GMP (c-di-GMP), a bacterial second messenger frequently implicated in biofilm formation, is synthesized and degraded by diguanylate cyclases (DGCs) and phosphodiesterases (PDEs), respectively. To characterize the c-di-GMP-metabolizing enzymes involved in L. pneumophila biofilm regulation, the consequences on biofilm formation and the c-di-GMP concentration of each corresponding gene inactivation were assessed in the Lens strain. The results showed that one DGC and two PDEs enhance different aspects of biofilm formation, while two proteins with dual activity (DGC/PDE) inhibit biofilm growth. Surprisingly, only two mutants exhibited a change in global c-di-GMP concentration. This study highlights that specific c-di-GMP pathways control L. pneumophila biofilm formation, most likely via temporary and/or local modulation of c-di-GMP concentration. Furthermore, Lpl1054 DGC is required to enable the formation a dense biofilm in response to nitric oxide, a signal for biofilm dispersion in many other species.     

New insights into the mechanism for clearance of apoptotic cells

Apoptosis is a physiological mechanism for the removal of unwanted or damaged cells. Apoptotic cells are rarely seen in living tissues, however, because of their rapid and efficient removal by phagocytosis. Phagocytotic cells such as macrophages or dendritic cells recognize apoptotic cells by specific changes of cell surface markers, which usually are not present on normal cells. One such event is the exposure of phosphatidylserine, which moves from the plasma membrane inner leaflet to the outer leaflet in preapoptotic cells. An unresolved problem, however, was the nature of the phosphatidylserine receptor on the phagocytotic cells. In a recent issue of Nature, Fadok et al. have reported the cloning of a phosphatidylserine receptor using an antibody raised against activated macrophages. Antibody treatment of these macrophages blocks this capacity to engulf.