Biological Phenomenon (biological + phenomenon)

Distribution by Scientific Domains

Selected Abstracts

Chlorophyll Catabolites , Chemical and Structural Footprints of a Fascinating Biological Phenomenon,

Simone Moser
Abstract Twenty years ago, the molecular basis for the seasonal disappearance of chlorophyll was still enigmatic. In the meantime, our knowledge on chlorophyll breakdown has grown considerably. As outlined here, it has been possible to decipher the basic transformations involved in natural chlorophyll breakdown by identification of chlorophyll catabolites in higher plants, and with the help of the synthesis of (putative) catabolic intermediates. In vascular plants, chlorophyll breakdown typically converts the green plant pigments efficiently into colorless and non-fluorescent tetrapyrroles. It involves colored intermediates only fleetingly and in an (elusive) enzyme-bound form. The non-fluorescent chlorophyll catabolites accumulate in the vacuoles of degreened leaves and are considered the products, primarily, of a detoxification process. However, they are effective antioxidants, and may thus also have physiologically beneficial chemical properties.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]


EVOLUTION, Issue 7 2003
Massimo Pigliucci
Abstract., The idea of genetic assimilation, that environmentally induced phenotypes may become genetically fixed and no longer require the original environmental stimulus, has had varied success through time in evolutionary biology research. Proposed by Waddington in the 1940s, it became an area of active empirical research mostly thanks to the efforts of its inventor and his collaborators. It was then attacked as of minor importance during the "hardening" of the neo-Darwinian synthesis and was relegated to a secondary role for decades. Recently, several papers have appeared, mostly independently of each other, to explore the likelihood of genetic assimilation as a biological phenomenon and its potential importance to our understanding of evolution. In this article we briefly trace the history of the concept and then discuss theoretical models that have newly employed genetic assimilation in a variety of contexts. We propose a typical scenario of evolution of genetic assimilation via an intermediate stage of phenotypic plasticity and present potential examples of the same. We also discuss a conceptual map of current and future lines of research aimed at exploring the actual relevance of genetic assimilation for evolutionary biology. [source]

Intrinsic aging vs. photoaging: a comparative histopathological, immunohistochemical, and ultrastructural study of skin

M. El-Domyati
Abstract: Cutaneous aging is a complex biological phenomenon affecting the different constituents of the skin. To compare the effects of intrinsic and extrinsic aging processes, a total of 83 biopsies were collected from sun-exposed and protected skin of healthy volunteers representing decades from the 1st to the 9th (6,84 years of age). Routine histopathology coupled with computer-assisted image analysis was used to assess epidermal changes. Immunoperoxidase techniques with antibodies against type I and type III collagens and elastin were used to quantitatively evaluate changes in collagen and elastic fibers and their ultrastructure was examined by transmission electron microscopy. Epidermal thickness was found to be constant in different decades in both sun-exposed and protected skin; however, it was significantly greater in sun-exposed skin (P = 0.0001). In protected skin, type I and III collagen staining was altered only after the 8th decade, while in sun-exposed skin the relative staining intensity significantly decreased from 82.5% and 80.4% in the 1st decade to 53.2% and 44.1% in the 9th decade, respectively (P = 0.0004 and 0.0008). In facial skin the collagen fiber architecture appeared disorganized after the 4th decade. The staining intensity of elastin in protected skin significantly decreased from 49.2% in the 1st decade to 30.4% in the 9th decade (P = 0.05), whereas in sun-exposed skin the intensity gradually increased from 56.5% in the 1st decade to 75.2% in the 9th decade (P = 0.001). The accumulated elastin in facial skin was morphologically abnormal and appeared to occupy the areas of lost collagen. Collectively, the aging processes, whether intrinsic or extrinsic, have both quantitative and qualitative effects on collagen and elastic fibers in the skin. [source]

HLA-G polymorphism in a Chinese Han population with recurrent spontaneous abortion

W. H. Yan
Summary Reproduction is an important biological phenomenon posing an immunological paradox because the semiallogeneic fetus survives by evading maternal immune recognition. The detailed mechanisms behind this maternal,fetal immunotolerance remain elusive. Human leucocyte antigen (HLA)-G, a non-classical HLA class I antigen, initially identified as a molecule selectively expressed on extravillous cytotrophoblasts and first studied in the context of pregnancy, has long been supposed to play a critical role in fetal,maternal immunotolerance. To investigate the role of HLA-G polymorphism in this process and whether the HLA-G genotype is associated with an increased risk for a subsequent miscarriage, 69 women with three or more recurrent spontaneous abortions (RSA) and 146 fertile control women were genotyped for the HLA-G locus in this study. To our knowledge, this is the first report on HLA-G polymorphism in RSA and in normal fertile women from a Chinese Han population. Nine HLA-G alleles were detected in the fertile control group; however, the allele HLA-G*0103 was absent in the RSA group. No statistical significance was observed in the distribution of HLA-G alleles between the two groups. The frequency of the null allele HLA-G*0105 N in the RSA group and in normal fertile women is 0.7% and 1.4%, respectively. Our data suggested that there was no association of HLA-G polymorphism with RSA. [source]

Orthogonal Chemical Genetic Approaches for Unraveling Signaling Pathways

IUBMB LIFE, Issue 6 2005
Kavita Shah
Abstract While chemical genetic approach uses small molecules to probe protein functions in cells or organisms, orthogonal chemical genetics refers to strategies that utilize reengineered protein-small molecule interfaces, to alter specificities, in order to probe their functions. The advantage of orthogonal chemical genetics is that the changes at the interfaces are generally so minute that it goes undetected by natural processes, and thus depicts a true physiological picture of biological phenomenon. This review highlights the recent advances in the area of orthogonal chemical genetics, especially those designed to probe signaling processes. Dynamic protein-protein and enzyme-substrate interactions following stimuli form the foundation of signal transduction. These processes not only break spatial and temporal boundaries between interacting proteins, but also impart distinct regulatory properties by creating functional diversity at the interfaces. Functional and temporal modulation of these dynamic interactions by specific chemical probes provides extremely powerful tools to initiate, ablate, decouple and deconvolute different components of a signaling pathway at multiple stages. Not surprisingly, multiple receptor-ligand reengineering approaches have been developed in the last decade to selectively manipulate these transient interactions with the aim of unraveling signaling events. However, given the diversity of protein-protein interactions and novel chemical genetic probes developed to perturb these processes, a short review cannot do adequate justice to all aspects of signaling. For this reason, this review focuses on some orthogonal chemical-genetic strategies that are developed to study signaling processes involving enzyme-substrate interactions. IUBMB Life, 57: 397-405, 2005 [source]

Ab initio computational study of positron emission tomography ligands interacting with lipid molecule for the prediction of nonspecific binding

Lula Rosso
Abstract Nonspecific binding is a poorly understood biological phenomenon of relevance in the study of small molecules interactions in vivo and in drug development. Nonspecific binding is thought to be correlated in part to a molecule's lipophilicity, typically estimated by measuring (or calculating) octanol,water partition coefficient. This is, however, a gross simplification of a complex phenomenon. In this article, we present a computational method whose aim is to help identify positron emission tomography (PET) ligands with low nonspecific binding characteristics by investigating the molecular basis of ligand,membrane interaction. We considered a set consisting of 10 well-studied central nervous system PET radiotracers acting on a variety of molecular targets. Quantum mechanical calculations were used to estimate the strength of the interaction between each drug molecule and one phospholipid molecule commonly present in mammalian membranes. The results indicate a correlation between the computed drug,lipid interaction energy and the in vivo nonspecific distribution volume relative to the free tracer plasma concentration, calculated using standard compartmental modeling for the analysis of PET data. Significantly, the drugs whose interaction with the lipid molecule more favorably possessed, in general, a higher nonspecific binding value, whereas for the drugs taken in consideration in this study, the water-octanol partition coefficient, log P, did not show good predictive power of the nonspecific binding. This study also illustrates how ab initio chemical methods may offer meaningful and unbiased insights for the understanding of the underlying chemical mechanisms in biological systems. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2008 [source]

Apoptosis: a basic biological phenomenon with wide-ranging implications in human disease

Abstract. Apoptosis is a highly regulated process of cell deletion and plays a fundamental role in the maintenance of tissue homeostasis in the adult organism. Numerous studies in recent years have revealed that apoptosis is a constitutive suicide programme expressed in most, if not all cells, and can be triggered by a variety of extrinsic and intrinsic signals. Many human diseases can be attributed directly or indirectly to a derangement of apoptosis, resulting in either cell accumulation, in which cell eradication or cell turnover is impaired, or cell loss, in which the apoptotic programme is inadvertently triggered. In addition, defective macrophage engulfment and degradation of cell corpses may also contribute to a dysregulation of tissue homeostasis. An increased understanding of the signalling pathways that govern the execution of apoptosis and the subsequent clearance of dying cells may thus yield novel targets for therapeutic intervention in a wide range of human maladies. [source]

Soft protein,protein docking in internal coordinates

Juan Fernández-Recio
PDB, Protein Data Bank; ICM, Internal Coordinate Mechanics; RMSD, root-mean-square deviation Abstract The association of two biological macromolecules is a fundamental biological phenomenon and an unsolved theoretical problem. Docking methods for ab initio prediction of association of two independently determined protein structures usually fail when they are applied to a large set of complexes, mostly because of inaccuracies in the scoring function and/or difficulties on simulating the rearrangement of the interface residues on binding. In this work we present an efficient pseudo-Brownian rigid-body docking procedure followed by Biased Probability Monte Carlo Minimization of the ligand interacting side-chains. The use of a soft interaction energy function precalculated on a grid, instead of the explicit energy, drastically increased the speed of the procedure. The method was tested on a benchmark of 24 protein,protein complexes in which the three-dimensional structures of their subunits (bound and free) were available. The rank of the near-native conformation in a list of candidate docking solutions was <20 in 85% of complexes with no major backbone motion on binding. Among them, as many as 7 out of 11 (64%) protease-inhibitor complexes can be successfully predicted as the highest rank conformations. The presented method can be further refined to include the binding site predictions and applied to the structures generated by the structural proteomics projects. All scripts are available on the Web. [source]

Reversal of benign prostate hyperplasia by selective occlusion of impaired venous drainage in the male reproductive system: novel mechanism, new treatment

ANDROLOGIA, Issue 5 2008
Y. Gat
Summary The prostate is an androgen-regulated exocrine gland producing over 30% of the noncellular components of the semen and promoting optimal conditions for survival and motility of sperm in the vagina. Benign prostate hyperplasia (BPH) is the most common benign neoplasm in men. Its aetiology is not clear, and therefore, current medical treatments are directed towards the symptoms. Though testosterone is known to be the promoter of prostate cell proliferation, no causal relation between serum testosterone levels and BPH has been found. In this study, we propose a novel and tested pathophysiological mechanism for the evolution of BPH and suggest a tested and effective treatment. We found that in all BPH patients, the one-way valves in the vertically oriented internal spermatic veins are destroyed (clinically manifested as varicocele), causing elevated hydrostatic pressure, some 6-fold greater than normal, in the venous drainage of the male reproductive system. The elevated pressure propagates to all interconnected vessels leading to a unique biological phenomenon: venous blood flows retrograde from the higher pressure in the testicular venous drainage system to the low pressure in the prostatic drainage system directly to the prostate (law of communicating vessels). We have found that free testosterone levels in this blood are markedly elevated, with a concentration of some 130-fold above serum level. Consequently, the prostate is exposed to: (i) increased venous pressure that causes hypertrophy; (ii) elevated concentration of free testosterone causing hyperplasia. We have treated 28 BPH patients using a technique that restores normal pressure in the venous drainage in the male reproductive system. The back-pressure and the back-flow of blood from the testicular to the prostate drainage system were eliminated and, consequently, a rapid reduction in prostate volume and a regression of prostate symptoms took place. [source]

Conditional gene silencing utilizing the lac repressor reveals a role of SHP-2 in cagA -positive Helicobacter pylori pathogenicity

CANCER SCIENCE, Issue 5 2004
Megumi Higuchi
RNA interference (RNAi) is a newly described biological phenomenon mediated by small interfering RNA (siRNA) that targets mRNA for degradation by cellular enzymes and has become a powerful method for studying gene functions in mammalian systems. The development of systems for inducing siRNA expression should enable examination of acute loss-of-function phenotypes in a cell of interest without the need to consider lethality or epigenetic adaptation of cells. We describe in this report an inducible siRNA expression system made by combined utilization of the RNA polymerase III-dependent promoter H1 and the bacterial lac repressor. Using this system, we established AGS gastric epithelial cells in which expression of SHP-2, a cellular tyrosine phosphatase known to specifically bind the Helicobacter pylori virulence factor CagA, is conditionally and reversibly silenced by the lactose analog isopropyl-1-thio-,-D-galactopyranoside (IPTG). Upon expression in AGS cells, CagA provoked a morphological transformation, termed the hummingbird phenotype, which is associated with CagA virulence. This morphogenetic activity of CagA was totally abolished when SHP-2 expression was silenced by inducible siRNA expression in AGS cells. Our results indicate that SHP-2 is a critical downstream effector of H. pylori CagA. The conditional gene silencing system described here should become a powerful tool for investigating the roles of cancer-related genes through a reversed genetic approach. [source]