Major Population (major + population)

Distribution by Scientific Domains
Distribution within Life Sciences

Selected Abstracts

Limitation of population recovery: a stochastic approach to the case of the emperor penguin

OIKOS, Issue 9 2009
Stéphanie Jenouvrier
Major population crashes due to natural or human-induced environmental changes may be followed by recoveries. There is a growing interest in the factors governing recovery, in hopes that they might guide population conservation and management, as well as population recovery following a re-introduction program. The emperor penguin Aptenodytes forsteri population in Terre Adélie, Antarctica, declined by 50% during a regime shift in the mid-1970s, when abrupt changes in climate and ocean environment regimes affected the entire Southern Ocean ecosystem. Since then the population has remained stable and has not recovered. To determine the factors limiting recovery, we examined the consequences of changes in survival and breeding success after the regime shift. Adult survival recovered to its pre-regime shift level, but the mean breeding success declined and the variance in breeding success increased after the regime shift. Using stochastic matrix population models, we found that if the distribution of breeding success observed prior to the regime shift had been retained, the emperor penguin population would have recovered, with a median time to recovery of 36 years. The observed distribution of breeding success after the regime shift makes recovery very unlikely. This indicates that the pattern of breeding success is sufficient to have prevented emperor penguin population recovery. The population trajectory predicted on the basis of breeding success agrees with the observed trajectory. This suggests that the net effect of any facors other than breeding success must be small. We found that the probability of recovery and the time to recovery depend on both the mean and variance of breeding success. Increased variance in breeding success increases the probability of recovery when mean success is low, but has the opposite effect when the mean is high. This study shows the important role of breeding success in determining population recovery for a long-lived species and demonstrates that demographic mechanisms causing population crash can be different from those preventing population recovery. [source]

Multi-directional differentiation of doublecortin- and NG2-immunopositive progenitor cells in the adult rat neocortex in vivo

Yasuhisa Tamura
Abstract In the adult mammalian brain, multipotent stem or progenitor cells involved in reproduction of neurons and glial cells have been well investigated only in very restricted regions; the subventricular zone of the lateral ventricle and the dentate gyrus in the hippocampal formation. In the neocortex, a series of in vitro studies has suggested the possible existence of neural progenitor cells possessing neurogenic and/or gliogenic potential in adult mammals. However, the cellular properties of the cortical progenitor cells in vivo have not been fully elucidated. Using 5,-bromodeoxyuridine labeling and immunohistochemical analysis of cell differentiation markers, we found that a subpopulation of NG2-immunopositive cells co-expressing doublecortin (DCX), an immature neuron marker, ubiquitously reside in the adult rat neocortex. Furthermore, these cells are the major population of proliferating cells in the region. The DCX(+)/NG2(+) cells reproduced the same daughter cells, or differentiated into DCX(+)/NG2(,) (approximately 1%) or DCX(,)/NG2(+) (approximately 10%) cells within 2 weeks after cell division. The DCX(+)/NG2(,) cells were also immunopositive for TUC-4, a neuronal linage marker, suggesting that these cells were committed to neuronal cell differentiation, whereas the DCX(,)/NG2(+) cells showed faint immunoreactivity for glutathione S-transferase (GST)-pi, an oligodendrocyte lineage marker, in the cytoplasm, suggesting glial cell lineage, and thereafter the cells differentiated into NG2(,)/GST-pi(+) mature oligodendrocytes after a further 2 weeks. These findings indicate that DCX(+)/NG2(+) cells ubiquitously exist as ,multipotent progenitor cells' in the neocortex of adult rats. [source]

Characterization of CC-chemokine receptor 7 expression on murine T cells in lymphoid tissues

IMMUNOLOGY, Issue 2 2003
Olle Bjorkdahl
Summary Expression of the lymph node homing and CC-chemokine receptor 7 (CCR7), with L-selectin (CD62L), has been shown to divide human memory T cells into two functionally distinct subsets. We generated a polyclonal antibody against murine CCR7 and used this antibody to study CCR7 expression on murine T-cell subsets. Using flow cytometric staining of T cells for visualisation expression of CCR7 in association with CD62L and CD44, a major population of CD4 or CD8 T cells expressing CCR7 were found to be CD62Lhigh CD44low, which would suggest a naïve cell phenotype. By analogy with human studies, memory cells could be subdivided into CCR7high CD62Lhigh CD44high (central memory) and CCR7low CD62Llow CD44high (effector memory). The proportions of these populations were different in lymph node, blood and spleen. Functional, short-term in vitro polyclonal stimulation of blood, spleen and lymph node cells from naive mice demonstrated that CCR7high CD4 T cells produced predominantly interleukin (IL)-2, whereas CCR7low CD4 T cells produced both IL-2 and interferon-, (IFN-,). However, in contrast to previously published reports, the CCR7high CD8 T-cell subpopulation produced both IFN-, and IL-2. Analysis of effector T cells, induced by immunization in vivo, showed that a proportion of activated naïve CD4 T cells down-regulated CCR7 only after multiple cell divisions, and this coincided with the down-regulation of CD62L and production of IL-4 and IFN-,. Finally, analysis of effector T cells during the phase of maximal clonal expansion of secondary immune responses in vivo indicated that the vast majority of both IL-2- and IFN-,-producing cells are CCR7low, while few cytokine-expressing CCR7high T cells were detected. Our results support the hypothesis, developed from studies with human cells, that CCR7 may separate functionally different murine memory T-cell subpopulations, but indicate additional complexity in that CCR7high CD8 T cells also may produce IFN-,. [source]

Prediction of response to treatment of chronic hepatitis B with pegylated interferon in the Philippines

Dorothy M. Agdamag
Abstract The response marker for interferon has not been investigated fully for hepatitis B viruses (HBVs) in the Philippines where novel subtypes B5 and C5 were recognized recently. The prediction parameters for interferon treatment were assessed, with emphasis on the mutation patterns in the basal core promoter and precore regions in patients with chronic hepatitis B. Seventeen HBeAg-positive patients were stratified according to response to treatment with pegylated interferon based on HBe seroconversion and HBV load. Intra-patient distributions of wild-type strains (A1762, G1764) and variants (T1762, A1764) were analyzed using HBV-DNA amplification and subsequent molecular cloning. The rate of variants (T1762, A1764) harbored by a patient was higher among responders (41.2% and 31% per person on average) than among non-responders (2.4% and 2.4%) to treatment with pegylated interferon at the baseline, respectively (P,<,0.05). The rate of variants (T1762, A1764) harbored by responders (41.2% and 31%) decreased to 1.7% and 1.7%, and wild-type strains (A1762, G1764) conversely became majority (98.3% and 98.3%) after treatment with pegylated interferon, respectively. HBV strains harbored by two of six responders and a patient with lower baseline load (1.0,×,104,copies/ml) showed genotype shift from A to other genotypes, where genotype A disappeared preferentially after the loss of HBeAg and genotypes B and C formed a major population. These results suggest that the HBV variants (T1762, A1764) and HBV genotype A in the Philippines have an advantage in the response to pegylated interferon. These results warrant a large-scale examination for further precise prediction of the response to treatment with interferon. J. Med. Virol. 82:213,219, 2010. © 2009 Wiley-Liss, Inc. [source]

P2X2, P2X2,2 and P2X5 receptor subunit expression and function in rat thoracolumbar sympathetic neurons

H. Schädlich
The present study investigated the pharmacological properties of excitatory P2X receptors and P2X2 and P2X5 receptor subunit expression in rat-cultured thoracolumbar sympathetic neurons. In patch-clamp recordings, ATP (3,1000 µm; applied for 1 s) induced inward currents in a concentration-dependent manner. Pyridoxal-phosphate-6-azophenyl-2,,4,-disulfonate (PPADS; 30 µm) counteracted the ATP response. In contrast to ATP, ,,,-meATP (30 µm; for 1 s) was virtually ineffective. Prolonged application of ATP (100 µm; 10 s) induced receptor desensitization in a significant proportion of sympathetic neurons in a manner typical for P2X2,2 splice variant-mediated responses. Using single-cell RT-PCR, P2X2, P2X2,2 and P2X5 mRNA expression was detectable in individual tyrosine hydroxylase-positive neurons; coexpression of both P2X2 isoforms was not observed. Laser scanning microscopy revealed both P2X2 and P2X5 immunoreactivity in virtually every TH-positive neuron. P2X2 immunoreactivity was largely distributed over the cell body, whereas P2X5 immunoreactivity was most distinctly located close to the nucleus. In summary, the present study demonstrates the expression of P2X2, P2X2,2 and P2X5 receptor subunits in rat thoracolumbar neurons. The functional data in conjunction with a preferential membranous localization of P2X2/P2X2,2 compared with P2X5 suggest that the excitatory P2X responses are mediated by P2X2 and P2X2,2 receptors. Apparently there exist two types of P2X2 receptor-bearing sympathetic neurons: one major population expressing the unspliced isoform and another minor population expressing the P2X2,2 splice variant. [source]

Effects of axotomy on telomere length, telomerase activity, and protein in activated microglia

Barry E. Flanary
Abstract The adult central nervous system (CNS) is generally thought of as a postmitotic organ. However, DNA labeling studies have shown that one major population of nonneuronal cells, called microglia, retain significant mitotic potential. Microglial cell division is prominent during acute CNS injury involving neuronal damage or death. Prior work from this laboratory has shown that purified microglia maintained in vitro with continual mitogenic stimulation exhibit telomere shortening before entering senescence. In the current study, we sought to investigate whether telomere shortening occurs in dividing microglia in vivo. For this purpose, we used a nerve injury model that is known to trigger localized microglial proliferation in a well-defined CNS region, the facial motor nucleus. Adult Sprague-Dawley rats underwent facial nerve axotomy, and facial motor nuclei were microdissected after 1, 4, 7, and 10 days. Whole tissue samples were subjected to measurements of telomere length, telomerase activity, and telomerase protein. Results revealed a tendency for all of these parameters to be increased in lesioned samples. In addition, microglial cells isolated directly from axotomized facial nuclei with fluorescence-activated cell sorting (FACS) showed increased telomerase activity relative to unoperated controls, suggesting that microglia are the primary cell type responsible for the increases observed in whole tissue samples. Overall, the results show that microglia activated by injury are capable of maintaining telomere length via telomerase during periods of high proliferation in vivo. We conclude that molecular mechanisms pertaining to telomere maintenance are active in the injured CNS. © 2005 Wiley-Liss, Inc. [source]

Solution conformation of a tetradecapeptide stabilized by two di- n -propyl glycine residues

Vijayalekshmi Sarojini
Abstract The solution conformation of a designed tetradecapeptide Boc-Val-Ala-Leu-Dpg-Val-Ala-Leu-Val-Ala-Leu-Dpg-Val-Ala-Leu-OMe (Dpg-14) containing two di- n -propyl glycine (Dpg) residues has been investigated by 1H NMR and circular dichroism in organic solvents. The peptide aggregates formed at a concentration of 3 mM in the apolar solvent CDCl3 were broken by the addition of 12% v/v of the more polar solvent DMSO-d6. Successive NiH Ni+1H NOEs observed over the entire length of the sequence in this solvent mixture together with the observation of several characteristic medium-range NOEs support a major population of continuous helical conformations for Dpg-14. Majority of the observed coupling constants () also support , values in the helical conformation. Circular dichroism spectra recorded in methanol and propan-2-ol give further support in favor of helical conformation for Dpg-14 and the stability of the helix at higher temperature. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd. [source]

Clearance of hepatitis C in chimpanzees is associated with intrahepatic T-cell perforin expression during the late acute phase

H. Watanabe
Summary., The liver is the primary site of hepatitis C virus (HCV) replication. Therefore, we undertook detailed intrahepatic studies of T-cell dynamics, apoptosis, and gene expression during the acute phase of infection using liver biopsies from chimpanzees that developed persistent infection or spontaneously cleared the virus. We examined more than 40 liver biopsies histologically and quantitatively for T-cell infiltration, hepatocyte apoptosis and perforin expression. These data were correlated with outcome and viral kinetics. We observed intrahepatic T-cell infiltration in both groups of animals with CD8+ T cells representing the major population. The appearance of T cells was always associated with apoptosis and mild alanine aminotransferase (ALT) elevations. Apoptosis (5,20% of hepatocytes) always occurred prior to serum ALT peak. Quantification of intrahepatic ALT mRNA revealed no upregulation of gene expression confirming that serum ALT increases were due to release of this enzyme from cells. During the late acute phase, cleared animals showed an increased frequency of hepatocyte apoptosis relative to persistently infected animals (P < 0.05). This correlated with a higher intrahepatic CD8+ T-cell frequency in the cleared group (P < 0.01) with a greater proportion of lymphocytes expressing perforin compared with the persistent group (P < 0.001). All infected animals mounted intrahepatic immune responses during the acute phase, but these were not maintained in frequency or efficacy in persistent infections. There is a reduction in the numbers of intrahepatic T cells during the late acute phase in infections that become persistent with significantly fewer of these cells functional in clearing the virus by killing infected hepatocytes. [source]

Grp94, the endoplasmic reticulum Hsp90, has a similar solution conformation to cytosolic Hsp90 in the absence of nucleotide

Kristin A. Krukenberg
Abstract The molecular chaperone, Hsp90, is an essential eukaryotic protein that assists in the maturation and activation of client proteins. Hsp90 function depends upon the binding and hydrolysis of ATP, which causes large conformational rearrangements in the chaperone. Hsp90 is highly conserved from bacteria to eukaryotes, and similar nucleotide-dependent conformations have been demonstrated for the bacterial, yeast, and human proteins. There are, however, important species-specific differences in the ability of nucleotide to shift the conformation from one state to another. Although the role of nucleotide in conformation has been well studied for the cytosolic yeast and human proteins, the conformations found in the absence of nucleotide are less well understood. In contrast to cytosolic Hsp90, crystal structures of the endoplasmic reticulum homolog, Grp94, show the same conformation in the presence of both ADP and AMPPNP. This conformation differs from the yeast AMPPNP-bound crystal state, suggesting that Grp94 may have a different conformational cycle. In this study, we use small angle X-ray scattering and rigid body modeling to study the nucleotide free states of cytosolic yeast and human Hsp90s, as well as mouse Grp94. We show that all three proteins adopt an extended, chair-like conformation distinct from the extended conformation observed for the bacterial Hsp90. For Grp94, we also show that nucleotide causes a small shift toward the crystal state, although the extended state persists as the major population. These results provide the first evidence that Grp94 shares a conformational state with other Hsp90 homologs. [source]

Characterization of electrochemical activity of a strain ISO2-3 phylogenetically related to Aeromonas sp. isolated from a glucose-fed microbial fuel cell

Kyungmi Chung
Abstract The microbial communities associated with electrodes in closed and open circuit microbial fuel cells (MFCs) fed with glucose were analyzed by 16S rRNA approach and compared. The comparison revealed that bacteria affiliated with the Aeromonas sp. within the Gammaproteobacteria constituted the major population in the closed circuit MFC (harvesting electricity) and considered to play important roles in current generation. We, therefore, attempted to isolate the dominant bacteria from the anode biofilm, successfully isolated a Fe (III)-reducing bacterium phylogenetically related to Aeromonas sp. and designated as strain ISO2-3. The isolated strain ISO2-3 could grow and concomitantly produce current (max. 0.24,A/m2) via oxidation of glucose or hydrogen with an electrode serving as the sole electron acceptor. The strain could ferment glucose, but generate less electrical current. Cyclic voltammetry supported the strain ISO2-3 was electrically active and likely to transfer electrons to the electrode though membrane-associated compounds (most likely c-type cytochrome). This mechanism requires intimate contact with the anode surface. Scanning electron microscopy revealed that the strain ISO2-3 developed multiplayer biofilms on the anode surface and also produced anchor-like filamentous appendages (most likely pili) that may promote long-range electron transport across the thick biofilm. Biotechnol. Bioeng. 2009; 104: 901,910. © 2009 Wiley Periodicals, Inc. [source]

CYP2C9 and CYP2C19 genetic polymorphisms: frequencies in the south Indian population

Rosemary Jose
Abstract The aim of the study was to establish the frequencies of CYP2C9*1, *2, *3 and CYP2C19*1, *2 and *3 in the south Indian population and to compare them with the inter-racial distribution of the CYP2C9 and CYP2C19 genetic polymorphisms. Genotyping analyses of CYP2C9 and CYP2C19 were conducted in unrelated, healthy volunteers from the three south Indian states of Andhra Pradesh, Karnataka and Kerala, by the polymerase chain reaction,restriction fragment-length polymorphism (PCR,RFLP). The allele frequencies of the populations of these three states were then pooled with our previous genotyping data of Tamilians (also in south India), to arrive at the distribution of CYP2C9 and CYP2C19 alleles in the south Indian population. Frequencies of CYP2C9 and CYP2C19 alleles and genotypes among various populations were compared using the two-tailed Fisher's exact test. The frequencies of CYP2C9*1, *2 and *3 in the south Indian population were 0.88 (95% CI 0.85,0.91), 0.04 (95% CI 0.02,0.06) and 0.08 (95% CI 0.06,0.11), respectively. The frequencies of CYP2C9 genotypes *1/*1, *1/*2, *1/*3, *2/*2, *2/*3 and *3/*3 were 0.78 (95% CI 0.74,0.82), 0.05 (95% CI 0.03,0.07), 0.15 (95% CI 0.12,0.18), 0.01 (95% CI 0.0,0.02), 0.01 (95% CI 0.0,0.02) and 0.0, respectively. CYP2C19*1, *2 and *3 frequencies were 0.64 (95% CI 0.60,0.68), 0.35 (95% CI 0.31,0.39) and 0.01 (95% CI 0.0,0.03), respectively. As a result of a significant heterogeneity, the data on CYP2C19 genotype frequencies were not pooled. The frequency of CYP2C9*2 mutant alleles in south Indians was higher than in Chinese and Caucasians, while CYP2C9*3 was similar to Caucasians. CYP2C19*2 was higher than in other major populations reported so far. The relatively high CYP2C19 poor-metabolizer genotype frequency of 12.6% indicates that over 28 million south Indians are poor metabolizers of CYP2C19 substrates. [source]

Dietary specialization and climatic-linked variations in extant populations of Ethiopian wolves

Jorgelina Marino
Abstract Understanding of the biology of rarity is central to the conservation of some endangered species. Rare taxa are often reported to be specialized, but they are usually poorly studied. The Ethiopian wolf (Canis simensis) is endemic to the Ethiopian highlands and in two major populations, Bale and Arsi in the southern range of the species, it preys almost exclusively upon diurnal rodents all year round, mainly molerats Tachyoryctes macrocephalus and common molerats T. splendens, respectively. Where these large rodents are absent or rare, wolves are expected to rely more heavily on nocturnal rats or livestock. Prey remains in 161 scats from five newly studied populations confirmed that wolves are indeed specialist rodent hunters elsewhere, and that their narrow diets are dominated by diurnal Murinae rats (60,83% of prey occurrences). Swamp rats Otomys typus were the main prey, followed by grass rats Arvicanthis abyssinicus. Common molerats, Lophuromys rats and nocturnal Stenocephalemys spp. constituted the variable portion of the diets, and their proportional contributions varied across populations in relation to elevation and latitude. Towards the north, where the climate is drier and human populations more dense, wolves predate more frequently on rat-sized prey, including nocturnal species, with implications for the survival of small populations in the Northern Highlands. Résumé Pour la conservation de certaines espèces en danger, il est essentiel de bien comprendre la biologie de la rareté. On rapporte souvent que des taxons rares sont spécialisés, mais ils sont généralement peu étudiés. Le loup d'Ethiopie Canis simensis est endémique des hauts plateaux éthiopiens et deux populations majeures, Bale et Arsi, dans la partie sud de leur aire de répartition, se nourrissent toute l'année presque exclusivement de petits rongeurs diurnes, surtout des rats-taupes géants Tachyoryctes macrocephalus et, plus communs, des rats taupes des montagnes T. splendens. Là où ces rongeurs sont absents ou rares, on s'attend à ce que les loups se nourrissent davantage de rats nocturnes ou de bétail. Des restes de proies identifiées dans 161 crottes de cinq nouvelles populations étudiées récemment ont confirmé que les loups sont bien, ailleurs, des chasseurs spécialisés en rongeurs et que leur régime alimentaire peu varié est dominé par des Murinae diurnes (60,83% des proies observées). Les rats des marais Otomys typusétaient les proies principales, suivis par les rats des herbes Arvicanthis abyssinicus. Les rats-taupes communs, les rats Lophuromys et les nocturnes Stenocephalemys spp. constituaient des portions variables du menu, et la proportion de leur contribution variait pour les populations en fonction de l'elevation et de la latitude. Vers le nord, là où le climat est plus sec et où la population humaine est plus dense, les loups s'attaquent plus souvent à des proies de la taille des rats, y compris des espèces nocturnes, ce qui a des implications pour la survie des petites populations des hauts plateaux du nord. [source]