Stability analysis of non-autonomous reaction-diffusion systems: the effects of growing domains

By using asymptotic theory, we generalise the Turing diffusively-driven instability conditions for reaction-diffusion systems with slow, isotropic domain growth. There are two fundamental biological differences between the Turing conditions on fixed and growing domains, namely: (i) we need not enforce cross nor pure kinetic conditions and (ii) the restriction to activator-inhibitor kinetics to induce pattern formation on a growing biological system is no longer a requirement. Our theoretical findings are confirmed and reinforced by numerical simulations for the special cases of isotropic linear, exponential and logistic growth profiles. In particular we illustrate an example of a reaction-diffusion system which cannot exhibit a diffusively-driven instability on a fixed domain but is unstable in the presence of slow growth.     

The role of fast and slow potassium currents in electrical activity of amphibian myelinated nerve fibres

The paper reviews the information about the role of fast and slow potassium currents in electrical activity of amphibian myelinated nerve fibres. It demonstrates the importance of discovering of fast and slow potassium currents and their following pharmacological separation (by potassium channels blockers 4-aminopyridine and tetraethylammonium) in investigation of mechanisms of biological potentials generation. The information about the existence of fast and slow potassium channels in the nerve membrane and about the properties of 4-aminopyridine and tetraethylammonium action served as a base for determination the nature of biological potentials and discovering the mechanism of potential-dependent action of 4-aminopyridine that for tens of years suffered from the lack of adequate explanation.     

描述和比较鱼类生长的快慢不宜使用生长指标(lgl_(t 1)-lgl_t)/0.4343)×l_t

生长率(l_(t 1)-(l_t))/l_t与生长指标((lgl_(t 1)-lgl_t)/0.4343)×l_t具有如下截然相反的数学特性：一个世代在t龄年初的平均体长l_t的年生长量l_(t 1)-l_t如果取常数值,则随着l_t增大,生长率单调减小表示生长减慢;但生长指标单调增大。由此可以看出,生长率符合而生长指标违背它们所要描述和比较的生长快慢固有的生物学概念。因此,有必要建议世界各国的鱼类生态学界停止使用生长指标。     

Mycobacterium tuberculosis Is Resistant to Isoniazid at a Slow Growth Rate by Single Nucleotide Polymorphisms in katG Codon Ser315

An important aim for improving TB treatment is to shorten the period of antibiotic therapy without increasing relapse rates or encouraging the development of antibiotic-resistant strains. In any M. tuberculosis population there is a proportion of bacteria that are drug-tolerant; this might be because of pre-existing populations of slow growing/non replicating bacteria that are protected from antibiotic action due to the expression of a phenotype that limits drug activity. We addressed this question by observing populations of either slow growing (constant 69.3h mean generation time) or fast growing bacilli (constant 23.1h mean generation time) in their response to the effects of isoniazid exposure, using controlled and defined growth in chemostats. Phenotypic differences were detected between the populations at the two growth rates including expression of efflux mechanisms and the involvement of antisense RNA/small RNA in the regulation of a drug-tolerant phenotype, which has not been explored previously for M. tuberculosis. Genotypic analyses showed that slow growing bacilli develop resistance to isoniazid through mutations specifically in katG codon Ser³¹⁵ which are present in approximately 50–90% of all isoniazid-resistant clinical isolates. The fast growing bacilli persisted as a mixed population with katG mutations distributed throughout the gene. Mutations in katG codon Ser³¹⁵ appear to have a fitness cost in vitro and particularly in fast growing cultures. Our results suggest a requirement for functional katG-encoded catalase-peroxide in the slow growers but not the fast-growing bacteria, which may explain why katG codon Ser³¹⁵ mutations are favoured in the slow growing cultures.     

Opioid-induced quantal slowing reveals dual networks for respiratory rhythm generation

Current consensus holds that a single medullary network generates respiratory rhythm in mammals. Pre-B?tzinger Complex inspiratory (I) neurons, isolated in transverse slices, and preinspiratory (pre-I) neurons, found only in more intact en bloc preparations and in vivo, are each proposed as necessary for rhythm generation. Opioids slow I, but not pre-I, neuronal burst periods. In slices, opioids gradually lengthened respiratory periods, whereas in more intact preparations, periods jumped nondeterministically to integer multiples of the control period (quantal slowing). These findings suggest that opioid-induced quantal slowing results from transmission failure of rhythmic drive from pre-I neurons to preB?tC I networks, depressed below threshold for spontaneous rhythmic activity. Thus, both I (in the slice), and pre-I neurons are sufficient for respiratory rhythmogenesis.     

Response to Selection at Two Temperatures for Fast and Slow Growth from Five to Nine Weeks of Age in Poultry

Cornell Control White Leghorn chicks were grown in a common environment to five weeks of age and selected for fast and slow gain in body weight from five to nine weeks of age at two temperatures, 21.1° (cold) and 32.2° (hot), during which time a constant 50% relative humidity was maintained. All lines were tested each generation in both temperature environments. Selection continued for four generations, with a second replicate started six weeks after the first replicate in each generation. In the hot environment, a 20% reduction (104 g) in five-to-nine-week weight gain was found. The responses to selection for fast and slow growth were symmetrical except in the first generation, when an outbreak of bronchitis confounded selection for body weight with selection for disease resistance and allowed little gain in the slow lines. No genotype-by-environment interactions were found, indicating that selection in either direction in either selection temperature produced equal responses in either test temperature. This suggests that any interactions observed between the growth of strains in tropical vs. temperate climates must be due to some difference between these environments other than the temperature differences studied.     

营巢类型、巢捕食和窝卵数对高寒草甸雀形目雏鸟生长期的影响

根据1998—2001年高寒草甸10种雀形目鸟类的窝卵数、雏期和巢捕食数据,以Logistic方程拟合雏鸟生长过程,并计算出有关生长率参数;根据营巢类型将10种雀形目鸟划分为开放或半开放类群(GOB)和全封闭穴居类群(HCB)两类,将把雏鸟的生长过程划分为3个生长期(缓增期、快增期和渐增期)。3个生长期占雏期的比例因营巢类型而异,GOB类群快增期>渐增期>缓增期;HCB类群渐增期>快增期>缓增期。分析营巢类型、巢捕食和窝卵数与各生长期之间的关系,结果表明3个生长期的体重积累占离巢时体重的比例因巢型不同而有显著差异;营巢类型和巢捕食显著影响各生长期占雏期的比例和体重积累占离巢时体重的比例;窝卵数影响快增期和渐增期长度,而不影响缓增期长度。快增期体重积累与渐增期的生长率不相关,但与渐增期长度显著相关。因此,前期的能量积累不影响后期生长率,而影响后期生长的长度。该结果进一步印证在晚成鸟中不存在补偿性生长。     

Expression of the human tumor suppressor p53 induces cell death in Pichia pastoris

The human tumor suppressor p53 is known as guardian of genome because of its involvement in many signals related to cell life or death. In this work, we report that human p53 induces cell death in the yeast Pichia pastoris. We showed a growth inhibition effect, which increased with the p53 protein expression level in recombinant Mut(s) (methanol utilization slow) strain of Pichia. However, no effect of p53 was observed in recombinant strain of Mut(+) (methanol utilization plus) phenotype. Interestingly, human p53 induces cell death in recombinant strains Mut(s) with characteristic markers of apoptosis such as DNA fragmentation, exposure of phosphatidylserine, and reactive oxygen species generation. Taken together, our results strongly suggest that human p53 is biologically active in this heterologous context. Thus, we propose that P.?pastoris could be a useful tool to better understand the biological function of human p53.     

黄花倒水莲生长与内源激素水平动态变化关系研究北大核心CSCD

为探索黄花倒水莲春梢生理生化特性的差异以及不同内源激素的变化规律,该文对黄花倒水莲春梢的生长动态进行监测,采用间接酶联免疫吸附法(ELISA)测定脱落酸(ABA)、生长素(IAA)、赤霉素(GA)、乙烯(ETH)和玉米素核苷(ZR)五种内源激素含量的动态变化,并对两者间的相关性进行分析。结果表明:(1)黄花倒水莲春梢生长发育过程可分为快速增长期(0~12 d)、生长转折期(16~20 d)和缓慢增长期(24~32 d)三个阶段。(2)内源激素ABA、GA、ETH和ZR含量在缓慢增长期显著高于快速增长期和生长转折期,IAA含量各时期差异较小。(3)春梢长、底部叶长和叶宽在快速增长期与ABA、GA、ETH和ZR含量呈负相关,且与ZR含量具有一定显著性,与IAA含量呈正相关;生长转折期,各指标与GA、ETH和ZR含量呈正相关,与GA含量具有一定显著性,与ABA含量呈负相关;缓慢增长期,各指标与五种内源激素含量均呈正相关,与IAA和ZR含量具有一定显著性。该研究结果为生产上利用外源激素调控黄花倒水莲春梢抽出以及生长提供了理论基础。     

Seasonal patterns of growth and nutrient status of the macroalga Adamsiella chauvinii (Rhodophyta) in soft sediment environments

The seasonal growth and nutrient status of the temperate subtidal macroalga Adamsiella chauvinii was determined at three soft sediment sites with different ranges of tidally-driven current speeds. A. chauvinii thalli exhibited maximum growth rates during the late summer (February) and no evidence of nitrogen limited growth in summer as often exhibited by macroalgae growing on hard substrata in temperate environments. We suggest that growth was maintained during the summer period, when seawater nitrogen concentrations were low, by localized sources of ammonium probably produced by sediments and fauna within the canopy. Growth rates were up to 50% lower at the site with the slowest water velocity throughout most of the experimental period. However a greater tissue nitrogen content of A. chauvinii thalli at the slow flow site did not support evidence for mass-transfer limitation. It is suggested that as a consequence of slow flow, sedimentation on blade surfaces reduced the amount of light available for photosynthesis and growth. Lower growth rates at the slow flow site reduced metabolic demand for nutrients resulting in accumulation of tissue nitrogen and phosphate.     

Deep-sea fishes in Canada’s Atlantic: population declines and predicted recovery times

Because of their slow growth rates, late maturity, low fecundity and long potential lifespans, deep-sea fishes are vulnerable to and theoretically slow to recover from overexploitation and bycatch. As industrial fishing moved into the deep sea, population declines were predicted and five species were shown to meet The World Conservation Union (IUCN) criteria for endangered species in Atlantic Canadian waters and two other deep-living species were listed as threatened by the Committee on the Status of Endangered Wildlife in Canada. We used data from scientific surveys to determine population trends in a 17-year time series for an additional 32 deep-sea fishes from the same geographic region. Eight species exhibited significant population declines, five increased, two were data deficient, and 17 showed no significant trends. Thus approximately 38% of the deep-sea bottom-living fishes in that well-investigated region could be at-risk, but definitive assignment to an IUCN category for most species is hampered by a lack of basic biological information, especially species specific generation times. Lack of biological information also limits efforts to determine possible recovery times, especially with respect to calculating intrinsic rates of population growth (r). For two Atlantic grenadiers (where r could be estimated using life-history parameters and standard life table techniques), the time to recovery with no fishing mortality could range from over a decade to over a century. This broad range results from the general uncertainty on life-history characteristics of these deep-sea species. Given the documented declines, the lack of basic data on life-history parameters, and the conservative assumption that recovery rates are likely to be prolonged, we argue that it is imperative to conduct additional studies pertaining to life history characteristics of deep-sea fishes and implement conservation measures in the deep sea immediately.     

Stretch and force generation induce rapid hypertrophy and myosin isoform gene switching in adult skeletal muscle.

Using electrical stimulation to control force generation and limb immobilization to alter the degree of stretch, we have studied the role of mechanical activity in inducing hypertrophy and in determining fast and slow muscle fibre phenotype. Changes in gene expression were detected by analysing the RNA in hybridization studies employing cDNA probes specific for fast and slow myosin heavy chains and other genes. As a result of overload in the stretched position, the fast contracting tibialis anterior muscle in an adult rabbit is induced to synthesize much new protein and to grow by as much as 30% within a period as short as 4 days. This very rapid hypertrophy was found to be associated with an increase of up to 250% in the RNA content of the muscles and an abrupt change in the species of RNA produced. Both stretch alone and electrical stimulation alone caused repression of the fast-type genes and activation of the slow-type genes. it appears that the fast-type IIB genes are the default genes, but that the skeletal slow genes are expressed as a response to overload and stretch. These findings have implications as far as athletic training and rehabilitation are concerned.     

Heterochronic differentiation of sexual dimorphs among Jurassic ammonite species

Ontogenetic and then heterochronic approaches are used here to analyze sexual differentiation within two well-known Jurassic dimorphic species. This analysis compares two ways of determining the relative biological age of ammonites, one using size (diameter) and the other the number of septa as a proxy of age. The shape standard is established from factor analysis of morphological and growth parameters. Size-age-shape relationships are analyzed on the basis of a new heterochronic representation. When diameter is used as a proxy of age, microconch morphs are globally considered to be progenetic compared with macroconch morphs. When size and age are determined separately and shape is included, (1) Ebrayiceras jactatum (microconch morph) has a shorter period of growth (progenesis) with acceleration of shape compared with its macroconch morph ( Morphoceras macrescens ), (2)( Cardioceras cordatum (microconch morph) has a shorter period of growth (progenesis) coupled with a slower rhythm of growth (dwarfism) compared with its macroconch morph. These findings emphasize the complex relationship between supposed sexual dimorphs in ammonites when size and age standards can be separated, as well as the need for an ontogenetic approach.     

Insulin-like growth factor (IGF)-I, IGF binding protein (IGFBP)-3, phosphoisoforms of IGFBP-1 and postnatal growth in very-low-birth-weight infants

Small preterm infants experience a unique postnatal period characterized by slow growth, inadequate nutrition and growth inhibiting treatments. Many have already been growth-restricted in utero. Studying this period is important when developing growth optimizing strategies for these infants and, in a broader context, as a model of extreme conditions that restrict growth. By following short-term growth of 48 very-low-birth-weight (VLBW; birth weight <1,500 g) infants for 9 postnatal weeks, we found that circulating insulin-like growth factor (IGF)-I and IGF binding protein (IGFBP)-3 levels are low and reflect rigorously measured (knemometry and weight) concurrent growth velocity. Moreover, weight growth velocity is correlated with the ratio of lesser to highly phosphorylated IGFBP-1 but not with absolute IGFBP-1 concentrations. Thus, IGF-I, IGFBP-3 and the phosphorylation status of IGFBP-1 in circulation are likely to be involved in growth regulation during the postnatal period in VLBW infants.     

Growth of a bacterium that apparently uses arsenic instead of phosphorus is a consequence of massive ribosome breakdown

A recent study (Wolfe-Simon, F., Switzer Blum, J., Kulp, T. R., Gordon, G. W., Hoeft, S. E., Pett-Ridge, J., Stolz, J. F., Webb, S. M., Weber, P. K., Davies, P. C., Anbar, A. D., and Oremland, R. S. (2011) Science 332, 1163-1166) described the isolation of a special bacterial strain, GFAJ-1, that could grow in medium containing arsenate, but lacking phosphate, and that supposedly could substitute arsenic for phosphorus in its biological macromolecules. Here, we provide an alternative explanation for these observations and show that they can be reproduced in a laboratory strain of Escherichia coli. We find that arsenate induces massive ribosome degradation, which provides a source of phosphate. A small number of arsenate-tolerant cells arise during the long lag period prior to initiation of growth in +As/-P medium, and it is this population that undergoes the very slow, limited growth observed for both E. coli and GFAJ-1. These results provide a simple explanation for the reported growth of GFAJ-1 in arsenate without invoking replacement of phosphorus by arsenic in biological macromolecules.     

Testing the Wiegand–Milton model: A long‐term experiment to understand mechanisms driving vegetation dynamics in arid shrublands

The Wiegand and Milton (1996) simulation model predicts that vegetation dynamics in arid shrublands are characterized by event‐driven stochasticity (weather events), and demographic inertia (persistence of a species in a community) that lead to a lagged response in vegetation compositional change. Slow plant growth is one of the mechanisms driving slow vegetation change. We test this model at the same location (Tierberg Long‐term Ecological Research site) on which the model was based. Three dwarf shrub species, differing in palatability, were tracked over 25 years (1988–2014) at two levels of the past herbivory (pre‐1960) and three levels of the present herbivory (post‐1988). In the period between 1960 and 1988, all sites were grazed at the recommended agricultural stocking rate. For each species, plant density and a number of size attributes (basal diameter, height, canopy area) were surveyed. Analyses using a two‐way Analysis of Covariance (ANCOVA) took initial starting size into consideration. As the model predicted, event‐driven stochasticity (rainfall) resulted in an increase in density of the smaller size classes following a single large recruitment event across all grazing regimes for the palatable and unpalatable species. Size‐class distribution curve types remained unchanged illustrating that population demography remains unaffected for long periods and responses are slow (lagged response). Slow plant growth was evident in that there were no changes in height, canopy area, or density under present grazing regimes over the 25‐year period. Palatable species had a reduced canopy area and density compared to unpalatable species. Our findings provide empirical evidence supporting the predictions of the Wiegand and Milton (1996) model, notably event‐driven stochasticity, demographic inertia, and a lagged response in vegetation change in arid shrublands. In addition, our results support the model assumption of the significance of slow growth in long‐lived plant species and the influence of grazing regime.     

Peptidoglycan turnover during growth recovery after chloramphenicol treatment in a Dap-Lys-mutant of Bacillus megaterium

The study of diaminopimelic acid (DAP) incorporation and turnover during growth recovery in chloramphenicol-treated (CMP-treated) Bacillus megaterium cells showed that two kinds of turnover occurred. A low acid-soluble turnover appeared as soon as growth resumed in bacteria labeled before the CMP treatment and at the middle of the first generation in those labeled during the treatment. The acid-insoluble turnover appeared only at the beginning of the second generation of growth resumption in bacteria labeled before CMP addition and at the beginning of the third generation in those labeled during the CMP treatment. The acid-soluble release observed during the period of cell wall thinning is too low to account for the decrease of the wall thickness and the acid-insoluble loss appears after this period. When bacteria were transferred into partially spent medium instead of fresh culture medium the acid-insoluble release started to appear half a generation sooner. Electron microscopic observations showed that in this case, large scales detached from the cell wall. This activity of wall degradation was not observed when the partially spent medium was previously heated for 10 min at 100 degree C. The persistence of a thick wall on cell ends during the first generation does not reflect an absence of growth sites because their labeling on autoradiographs is high. Rather, it seems to be due to a low lytic activity at the poles.     

Maternal protein restriction during lactation induces early and lasting plasma metabolomic and hepatic lipidomic signatures of the offspring in a rodent programming model

Perinatal undernutrition affects not only fetal and neonatal growth but also adult health outcome, as suggested by the metabolic imprinting concept. However, the exact mechanisms underlying offspring metabolic adaptations are not yet fully understood. Specifically, it remains unclear whether the gestation or the lactation is the more vulnerable period to modify offspring metabolic flexibility. We investigated in a rodent model of intrauterine growth restriction (IUGR) induced by maternal protein restriction (R) during gestation which time window of maternal undernutrition (gestation, lactation or gestation–lactation) has more impact on the male offspring metabolomics phenotype. Plasma metabolome and hepatic lipidome of offspring were characterized through suckling period and at adulthood using liquid chromatography–high-resolution mass spectrometry. Multivariate analysis of these fingerprints highlighted a persistent metabolomics signature in rats suckled by R dams, with a clear-cut discrimination from offspring fed by control (C) dams. Pups submitted to a nutritional switch at birth presented a metabolomics signature clearly distinct from that of pups nursed by dams maintained on a consistent perinatal diet. Control rats suckled by R dams presented transiently higher branched-chain amino acid (BCAA) oxidation during lactation besides increased fatty acid (FA) β-oxidation, associated with preserved insulin sensitivity and lesser fat accretion that persisted throughout their life. In contrast, IUGR rats displayed permanently impaired β-oxidation, associated to increased glucose or BCAA oxidation at adulthood, depending on the fact that pups experienced slow postnatal or catch-up growth, as suckled by R or C dams, respectively. Taken together, these findings provide evidence for a significant contribution of the lactation period in metabolic programming.     

Development of laboratory diagnostic methods for slow infections of the human central nervous system caused by nonclassical viruses

The theoretical foundations of the laboratory diagnosis of Creutzfeldt-Jakob disease and amyotrophic leukospongiosis in living patients are discussed and practical diagnostic methods are proposed on the basis of the study of the biological properties of nonclassical viruses and the pathogenesis of slow infections of the central nervous system. The use of the retrobulbar method of infecting susceptible animals has permitted, besides a considerable decrease in the incubation period in modeling slow infections, the improvement of the in vivo biological test. Thus, as the result of the multiplication of non-classical viruses in the visual nerve and the retina, experimental animals develop retinopathy which can be detected 1.5-2.5 weeks after the animals are injected with the spinal fluid or blood taken from the patient under examination. To diagnose amyotrophic leukospongiosis, the in vitro biological test, based on the capacity of the causative agent for inducing a considerable (2- to 5-fold) increase in the mitotic activity of HEp-2 cells, has been developed. The comparative studies have shown the expediency of using the method for the detection of antibodies to nerve-fiber proteins as an additional test for the differential diagnosis of slow infections of the central nervous system.