Involvement of β-Carotene in the Antioxidant Defense of the Bacterial Cell

Effects of recombinant -carotene on the resistance of E. coli culture to menadione and paraquat were studied. The presence of -carotene in E. coli cells prevented, to a considerable extent, an increase in superoxide dismutase activity (induced by redox mediators) without affecting the culture growth. These findings suggest that -carotene is involved in the defense of cells against oxidative stress.     

Structurization of Cortical Layer of Loach Yolk Cell after Wounding as a “Minimal” Model of Morphogenesis

Structural rearrangements of the yolk cell surface were studied in loach embryos using SEM and TEM, which take place within 30 min after a point-like puncture at the late blastula stage. The effects of sucking off or addition of a part of yolk, lowered temperature, and absence of Ca²⁺ on structurization were studied. Around the area of puncture, the yolk granules were submerged, the number of vesicles increased, and numerous membrane folds were formed. The folds were aggregated to form two sharply distinct types of structures: a group of rounded evaginations around the site of puncture and a system of radial folds in the periphery. Small radial folds are aggregated in radial strands, several dozens folds in each. Sucking off a part of yolk accelerated the above processes, while addition of yolk, cooling, and absence of Ca²⁺ in the incubation medium slowed down or suppressed these processes. The observed structurization can be considered as self-organization at the level of the yolk cell cortical level, largely similar to that during normal morphogenesis at the level of multicellular sheets. Hence, the membrane dynamics in the yolk cell wall after its damage can be considered as one of simplified (minimal) models of morphogenesis. A study of this model makes it possible to narrow down the circle of factors essential for self-organization of morphogenetic processes.     

Assembly of the Murine Leukemia Virus Is Directed towards Sites of Cell–Cell Contact

We have investigated the underlying mechanism by which direct cell–cell contact enhances the efficiency of cell-to-cell transmission of retroviruses. Applying 4D imaging to a model retrovirus, the murine leukemia virus, we directly monitor and quantify sequential assembly, release, and transmission events for individual viral particles as they happen in living cells. We demonstrate that de novo assembly is highly polarized towards zones of cell–cell contact. Viruses assembled approximately 10-fold more frequently at zones of cell contact with no change in assembly kinetics. Gag proteins were drawn to adhesive zones formed by viral Env glycoprotein and its cognate receptor to promote virus assembly at cell–cell contact. This process was dependent on the cytoplasmic tail of viral Env. Env lacking the cytoplasmic tail while still allowing for contact formation, failed to direct virus assembly towards contact sites. Our data describe a novel role for the viral Env glycoprotein in establishing cell–cell adhesion and polarization of assembly prior to becoming a fusion protein to allow virus entry into cells.     

Revisiting the “Cdk-Centric” View of the Mammalian Cell Cycle

Since the early genetic studies in yeast, regulation of the cell cycle has been associated to the sequential activation of several proline-directed serine-threonine protein kinases by cyclins. From yeast to humans, the activiy of these cyclin-dependent kinases (Cdks) have been thought to be essential for cell cycle regulation. Recent gene-targeted mouse models for different cyclins and Cdks have shown that members of these families show a certain level of redundancy and that specific complexes are not required for the mitotic cell cycle. However, the complexity of the Cdk-cyclin network and the promiscuity of their members makes it difficult to understand the relative contribution of these proteins to the mammalian cell division cycle. Compensatory roles by non-Cdk activities and Cdk-independent functions of cyclins are increasing the complexity of the current simplistic models. We still do not know whether at least one cyclin-dependent kinase activity is required for cell cycle progression in mammalian cells. Indeed, a relevant question for cancer therapy.     

Cell Research Announces the Appointment of New Deputy Editor-in-chief

Cell Research is pleased to announce that Dr Dangsheng Li has been appointed as thenew Deputy Editor-in-chief for our journal,starting March 2006.Dangsheng received hisBS degree(in Cell Biology)from the University of Science and Technology of China,and obtained his PhD(in Molecular Biology)from Cornell University Graduate School ofMedical Sciences.After extensive postdoctoral training at New York University MedicalCenter,he joined Cell Press in 2004 to serve as an Associate Editor for the premium biol-ogy journal Cell.Dangsheng will be in charge of the scientific editing operations of Cell     

Studies on the Cell Wall of Piricularia oryzae†

The chemical constituents of the cell wall of Piricularia oryzae, the pathogenic fungus of rice blast disease, were studied with the aids of chemical analysis, X-ray diffraction, infra-red absorption and enzymatic degradation. The sugar constituents were identified by chromatography as glucose (62%), mannose (4%), galactose (0.5%), and hexosamine (13%). The acidic amino acid rich protein was comprised 4.6% in the cell wall. The cell wall consists of at least three different polysaccharide complexes: a) α-Heteropolysaccharide protein complex containing mannose, glucose and galactose, b) β-1,3-Glucan containing β-1, 6-linked branch, c) Chitin like substance.     

α-Fetoprotein-Producing Non-Germ Cell Tumors of the Urological System

Elevated serum levels of α-fetoprotein (AFP), a fetal serum protein, occur mainly in the development of hepatocellular carcinoma (HCC) or germ cell tumors, mainly yolk sac tumor. Rarely, other tumors of the urological system produce AFP. This article reviews the AFP-producing non-germ cell tumors of the urological tract reported to date. These include different types of tumors of the adrenal glands, kidney, ureter, urinary bladder, and testis. It is important for pathologists, urologists, and oncologists to be aware of such cases as the diagnosis affects the management plan for the patient.     

Developmental and Stress-Induced Remodeling of Cell–Cell Communication in the Adrenal Medullary Tissue

The adrenal medullary tissue contributes to maintain body homeostasis in reaction to stressful environmental changes via the release of catecholamines into the blood circulation in response to splanchnic nerve activation. Accordingly, chromaffin cell stimulus-secretion coupling undergoes temporally restricted periods of anatomo-functional remodeling in response to prevailing hormonal requirements of the organism. The postnatal development of the adrenal medulla and response to stress are remarkable physiological situations in which the stimulus-secretion coupling is critically affected. Catecholamine secretion from rat chromaffin cells is under a dual control involving an incoming initial command arising from the sympathetic nervous system that releases acetylcholine at the splanchnic nerve terminal-chromaffin cell synapses and a local gap junction-mediated intercellular communication. Interestingly, these two communication pathways are functionally interconnected within the gland and exhibit coordinated plasticity mechanisms. This article reviews the physiological and molecular evidence that the adrenal medullary tissue displays anatomical and functional adaptative remodeling of cell–cell communications upon physiological (postnatal development) and/or physiopathological (stress) situations associated with specific needs in circulating catecholamine levels.     

Junctional Music that the Nucleus Hears: Cell–Cell Contact Signaling and the Modulation of Gene Activity

Cell–cell junctions continue to capture the interest of cell and developmental biologists, with an emerging area being the molecular means by which junctional signals relate to gene activity in the nucleus. Although complexities often arise in determining the direct versus indirect nature of such signal transduction, it is clear that such pathways are essential for the function of tissues and that alterations may contribute to many pathological outcomes. This review assesses a variety of cell–cell junction-to-nuclear signaling pathways, and outlines interesting areas for further study.The evolution of multicellular life forms has to a significant extent involved refinements of each cell''s capacity to sense the state of its directly contacting neighbors. This exchange of information often occurs within tissues, with the result that gene activity in the nucleus is altered or maintained accordingly. In this article, we focus on how signals arise at cell–cell junctions and are transduced to the nucleus; we do not include discussion of mechanical/cytoskeletal signals influencing nuclear decisions, and the reader is directed to a recent review of this topic (Ingber 2008).An issue that arises when addressing cell–cell junction(s), referred to as CCJ(s), -to-nuclear signals, is that homotypic or heterotypic junctional proteins responsible for conferring adhesive activity are often in a much larger complex of proteins. These interactions may be either in cis (interacting within the plasma membrane of the cell) or trans orientations (interacting through ectodomain contacts extended between cells). Most of these transmembrane proteins are likely to have the potential to contribute to downstream signaling events, and many may associate with one another only under specific physiological conditions. For example, certain receptor tyrosine kinases (RTKs) associate with particular cadherins, and when associated are relevant to that cadherin''s functions (Wheelock and Johnson 2003; Andl and Rustgi 2005). In this article, we discuss relationships such as these in the context of CCJ-nuclear signaling. A topic not represented here is the CCJ signaling of immune surveillance cells, for example, pathways activated following leukocyte–endothelia contact. This area is of great basic and biomedical interest, but is addressed elsewhere (Dustin 2007).We focus on signaling by a select number of junction types, including adherens, desmosomal, and tight junctions, and to a lesser extent, gap junctions. Details of the structure and function of each of these junctions are presented in other articles (see Meng and Takeichi 2009, Delva et al. 2009, Furuse 2009, and Goodenough and Paul 2009, respectively). These junctions are often represented in textbooks as distinct entities in the context of epithelial tissues, but their structures and how they respond to or generate signaling cues vary according to cellular context. Select components within these junctions may be shared, for example between desmosomal, adherens, and tight junctions, and in some instances, intimate physical proximities are likely to advance these junctions'' functional interrelation. Further, different cell types show less common junctional organizations (Straub et al. 2003; Wuchter et al. 2007), such that the total spectrum of CCJ signals is likely to be impressive, and far beyond what is currently known or understood. Given the interdependence of cell neighbors in forming and maintaining cell groupings, high diversity and sophistication arose in complex organisms, both in CCJ structures themselves and their associated nuclear signaling pathways. Compared with the knowledge accumulated over the past two decades on cell–extracellular matrix signaling via integrins (Abram and Lowell 2009), we know less about signals initiated from forming or mature cell–cell contacts in epithelial, neural, or endothelial tissues. Thus, as the field moves forward, there is the potential to achieve a deepened understanding of how the cell–extracellular matrix and cell–cell adhesion systems are coupled in a signaling context, and how they collectively relate to the adhesion, motility, and differentiation of cells and tissues.     

Argonaute2 Mediates Compensatory Expansion of the Pancreatic β Cell

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Is the Cell Membrane a Universal Rate-Limiting Barrier to the Movement of Water between the Living Cell and Its Surrounding Medium?

With the use of a newly introduced technique, the "influx profile analysis," we studied the diffusion of tritiated water in and out of frog ovarian eggs at 25°C. The results show that the rate-limiting step in the exchange of labeled water is not permeation through the cell membrane but diffusion in the bulk of the intracellular water.     

Biochemistry of Direct Cell−Cell Interactions. Signaling Factors Regulating Orchestration of Cell Populations

Biochemical mechanisms for the orchestration of cell populations are discussed in view of direct cell?cell inter-actions and composition of the intercellular medium. In our works of the last 20 years, we used circahoralian (ultradian) rhythm of protein synthesis as a marker of cell interactions. Experiments in cell cultures are described; some influences on the organism native medium were performed. Information is presented on the signaling membrane factors that trigger a cascade of processes in the cytoplasm and lead to the orchestration of cell activity in vitro and in vivo. Among these factors are blood serum neurotransmitters, gangliosides, and some hormones. Studying protein synthesis kinetics allowed us to understand the importance of maintaining the constant levels of signaling factors in mammalian blood. The literature on protein phosphorylation as a key process of cell organization is reviewed. The persistence of the organizing signal for several days is described as a type of cell “memory”. It seems promising to extend the area for application of direct cell?cell interactions (respiration of cells, proliferation, etc.) to study possibilities of epigenetic regulation. It is important to continue the studies on the mechanisms of biochemical action of the known drugs as signaling factors.     

Effect of X-Irradiation at Different Stages in the Cell Cycle on Individual Cell–Based Kinetics in an Asynchronous Cell Population

Using an asynchronously growing cell population, we investigated how X-irradiation at different stages of the cell cycle influences individual cell–based kinetics. To visualize the cell-cycle phase, we employed the fluorescent ubiquitination-based cell cycle indicator (Fucci). After 5 Gy irradiation, HeLa cells no longer entered M phase in an order determined by their previous stage of the cell cycle, primarily because green phase (S and G2) was less prolonged in cells irradiated during the red phase (G1) than in those irradiated during the green phase. Furthermore, prolongation of the green phase in cells irradiated during the red phase gradually increased as the irradiation timing approached late G1 phase. The results revealed that endoreduplication rarely occurs in this cell line under the conditions we studied. We next established a method for classifying the green phase into early S, mid S, late S, and G2 phases at the time of irradiation, and then attempted to estimate the duration of G2 arrest based on certain assumptions. The value was the largest when cells were irradiated in mid or late S phase and the smallest when they were irradiated in G1 phase. In this study, by closely following individual cells irradiated at different cell-cycle phases, we revealed for the first time the unique cell-cycle kinetics in HeLa cells that follow irradiation.     

Activation of the B Cell Receptor Leads to Increased Membrane Proximity of the Igα Cytoplasmic Domain

Binding of antigen to the B cell receptor (BCR) induces conformational changes in BCR''s cytoplasmic domains that are concomitant with phosphorylation of the immunoreceptor tyrosine-based activation motifs (ITAMs). Recently, reversible folding of the CD3ε and ξ chain ITAMs into the plasma membrane has been suggested to regulate T cell receptor signaling. Here we show that the Igα and Igβ cytoplasmic domains of the BCR do not associate with plasma membrane in resting B cells. However, antigen binding and ITAM phosphorylation specifically increased membrane proximity of Igα, but not Igβ. Thus, BCR activation is accompanied by asymmetric conformational changes, possibly promoting the binding of Igα and Igβ to differently localized signaling complexes.