Dose-dependent increase or decrease of somatic intrachromosomal recombination produced by etoposide

Chromosomal inversions and deletions can occur via somatic intrachromosomal recombination (SICR), a mechanism known to be important in mutagenesis and carcinogenesis. Here, we demonstrate a dose-dependent increase or decrease in SICR inversion frequency both in vivo and in vitro after treatment with etoposide, using the pKZ1 mouse mutagenesis model. pKZ1 mice received a single intraperitoneal injection of etoposide dose ranging from 0.0005 to 50mg/kg. Animals were sacrificed 3 days after treatment and the spleen was analysed for SICR. A significant 1.4-3.1-fold induction of SICR inversion events was detected in pKZ1 mice after treatment with etoposide doses ranging from 0.05 to 50 mg/kg etoposide. However, inversion frequencies after treatment with 0.0005 and 0.005 mg/kg etoposide decreased significantly to 0.67 and 0.43 of the levels observed in control animals, respectively. A pKZ1 mouse hybridoma cell line was exposed to etoposide (1-1000 nM) and a similar pattern of SICR response to that detected in vivo was observed. A significant 2.3-4.6-fold induction of SICR inversions was observed in pKZ1 cells treated with 100 and 1000 nM etoposide. Inversion frequencies after treatment with 1 and 10nM etoposide decreased significantly to 0.31 and 0.5 of the level observed in control cell lines. Our in vitro studies complement our in vivo studies and exclude a kinetic phenomenon as the responsible mechanism of reduction in SICR in response to low dose etoposide. Determination of the exact mechanism and significance of recombination suppression at low doses of etoposide treatment requires further investigation.     

An increase or a decrease in myosin II phosphorylation inhibits macrophage motility

Myosin II purified from mammalian non-muscle cells is phosphorylated on the 20-kD light chain subunit (MLC20) by the Ca2+/calmodulin-dependent enzyme myosin light chain kinase (MLCK). The importance of MLC20 phosphorylation in regulating cell motility was investigated by introducing either antibodies to MLCK (MK-Ab) or a Ca2+/calmodulin-independent, constitutively active form of MLCK (MK-) into macrophages. The effects of these proteins on cell motility were then determined using a quantitative chemotaxis assay. Chemotaxis is significantly diminished in macrophages containing MK-Ab compared to macrophages containing control antibodies. Moreover, there is an inverse relationship between the number of cells that migrate and the amount of MK-Ab introduced into cells. Interestingly, there is also an inverse relationship between the number of cells that migrate and the amount of MK- introduced into cells. Other experiments demonstrated that MK-Ab decreased intracellular MLC20 phosphorylation while MK- increased MLC20 phosphorylation. MK- also increased the amount of myosin associated with the cytoskeleton. These data demonstrate that the regulation of MLCK is an important aspect of cell motility and suggest that MLC20 phosphorylation must be maintained within narrow limits during translational motility by mammalian cells.     

The effects of a sudden decrease or increase in daylength on prolactin secretion in the ram

Six adult Soay rams were preconditioned to an artificial lighting regimen of alternating 4-month periods of long (16L:8D) and short days (8L:16D) for at least 10 months before blood samples were collected at hourly intervals for 24 h at various times. The abrupt change from long to short days resulted in a progressive decrease in plasma levels of prolactin, while that from short to long days had the reverse effect; the first response to the light changes was rapid, beginning within 6 days. During the periods of high secretion there was a 24-h cycle in plasma prolactin concentrations, with a peak in both the early dark and early light phases of each day. Changes in the relative magnitude of these peaks were observed in relation to the long-term alteration in prolactin secretion. Plasma levels of FSH were also measured and a close inverse relationship between gonadotrophin and prolactin secretion was observed.     

Oceanographic drivers of offspring abundance may increase or decrease reproductive variance in a temperate marine fish

In species that reproduce into uncertain environments, the relationship between mean reproductive success (the abundance of new recruits) and the variance in reproductive success (whether adults contribute disproportionally more offspring) may not be straightforward because of stochastic environmental processes that create high variance in reproductive success among adults. In this study, we investigated the relationships between oceanography, reproductive success and reproductive variance in the black rockfish, Sebastes melanops, a long‐lived temperate reef fish with pelagic larvae. We quantified black rockfish recruitment, genetic diversity and growth rates from otolith microstructure over 5 years (2005–2009) during which oceanographic conditions differed. We used cross‐correlations to determine windows of time during which oceanographic variables were significantly correlated with the resulting abundance or genetic diversity of recruits. We found that warmer ocean temperatures were positively correlated with the abundance of recruits, as well as the effective number of breeders. In contrast, the strength of coastal upwelling during settlement was positively correlated with the annual abundance of new recruits, but was negatively correlated with the effective number of breeders. Larval growth rates were explained substantially more by temperature than by upwelling and suggested that temperature affected survival through growth, while upwelling affected survival through transport. Our results indicated that cold ocean temperatures and intense upwelling caused sweepstakes‐like processes to operate on black rockfish populations, despite high abundances of recruits. We propose that a decoupling of the mean and variance in reproductive success may be characteristic of organisms that reproduce into uncertain environments.     

陕西不同地区栓皮栎种群增长模拟与预测预报的研究

时间序列分析可以通过差分、周期的方法,对植物种群的增长进行模拟与预测。在陕西的秦岭、汉中、黄龙地区选择林相整齐、有代表性的地段作为标准地,设置样方40个,对各样方内的林木进行每木检尺,通过优势木解析的方法,测得栓皮栎种群胸径的实际生长量,运用起伏型时间序列分析,建立了栓皮栎种群个体年龄与胸径生长的时间序列模型,四个模型所得的各个样地栓皮栎胸径生长的模拟值与实际值进行比较,其模拟平均误差都在1．5％以内,平均精度达到97．8％,模拟效果较好。经检验,该模型预测胸径的生长量具有较好的可靠性和精度高等优点,从而丰富和发展了种群增长模拟与预测预报的方法。     

Interactions between xenobiotics that increase or decrease the levels of cytochrome P-450 isozymes in rabbit lung and liver

Isozyme-specific enzymatic activities, radial immunodiffusion, and Western blotting were used to study the effects of phenobarbital, Aroclor 1260, and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on microsomal levels of cytochrome P-450 forms 2, 5, and 6. The pulmonary concentration of form 2 was decreased to trace levels by the administration of Aroclor 1260 but not TCDD; co-administration of phenobarbital did not mitigate the decrease. The pulmonary concentration of form 5 was not significantly changed following treatment with Aroclor 1260, phenobarbital, or TCDD. The pulmonary content of form 6 was increased 5- and 10-fold by administration of Aroclor 1260 and TCDD, respectively, and decreased 2-fold by treatment with phenobarbital. Further, phenobarbital antagonized the induction of form 6 by Aroclor 1260 but not by TCDD. In the liver, increases and decreases in form 2-mediated benzphetamine N-demethylation were observed following treatment with Aroclor 1260 depending on the time after dose and individual rabbit response. Hepatic induction of form 2 by phenobarbital was significantly decreased by co-administration of Aroclor 1260. However, form 5 was induced in the liver by either Aroclor 1260 or phenobarbital or both. Thus, the effect of Aroclor 1260 on the control of the concentration of form 2 is independent of that of form 5 in the lung and liver. Fractionation of the Aroclor 1260 to remove co-planar polychlorinated biphenyls and dibenzofurans was useful in demonstrating that the pulmonary induction of form 6 was dependent on these components and unrelated to the repression of form 2 in the lung and liver. The apparent repressive effect of phenobarbital on form 6 in the lung is interesting as it suggests an interaction between phenobarbital and polycyclic hydrocarbon-mediated induction.     

How to increase the population of a Phlebotomus perniciosus (Diptera: Psychodidae) colony: a new method

The sandfly Phlebotomus perniciosus is the most widespread vector of Leishmania infantum in Spain. Laboratory colonisation represents the most feasible source of information on the biology of these insects, but in conducting any study, the density of individuals in the colony may drop to such an extent that it is sometimes difficult to recover the initial population levels. A new technique was tested for the recovery of sandfly eggs in three different colonies; the recovery rate was studied by comparing the standard method of mass rearing with this new method of colony management. The results demonstrate a mean increase of 18.4% in adult production, a growth in colony productivity that justifies the inclusion of this process in the routine maintenance of any colony of sandflies.     

一种含特异性侵染内共生菌Rickettisa massilia的烟粉虱种群建立方法

【目的】烟粉虱Bemisia tabaci(Gennadaius)广泛分布于全球除南极洲外各大洲的90多个国家和地区,其寄主范围广,危害严重,属于农业上的重要害虫。烟粉虱体内的内共生菌有助于其扩散传播,提高其寄主适合度,但其体内的内共生菌大都为次生内共生菌,很难进行体外培养,因此,加大了其内共生菌研究的难度。【方法】采集我国部分地区的烟粉虱种群,然后利用基于mt DNA COⅠ基因的种特异性引物进行种群生物型鉴定,再用内共生菌的特异性引物来鉴定含有特异性侵染内共生菌种群,确定个体含内生菌类型后,采取继代饲养方法建立种群。【结果】经鉴定烟粉虱的生物型为Q型(MED隐种),经过5代种群筛选后,可以建立稳定遗传的含特异性侵染内共生菌Rickettisa massilia菌的烟粉虱种群。【结论】通过本方法可以获得稳定的含有特异性侵染内共生菌Rickettisa massilia菌的烟粉虱种群。该方法对研究烟粉虱与体内内共生菌、植物三者之间以及烟粉虱体内某几种内共生菌之间的互作有重要意义,同时也为明确烟粉虱体内Rickettisa菌的作用研究打下基础。     

An apparent population decrease,or change in distribution,of Weddell seals along the Victoria Land coast

Ground counts during 1959–1968 compared with counts using high resolution (0.6 m²) satellite imagery during 2008–2012 indicated many fewer Weddell seals (Leptonychotes weddellii) at two major molting areas in the western Ross Sea: Edisto Inlet‐Moubray Bay, northern Victoria Land, and McMurdo Sound, southern Victoria Land. Breeding seals have largely disappeared from Edisto‐Moubray, though the breeding population in McMurdo Sound appears to have recovered from harvest in the 1960s. The timing of decline, or perhaps spreading (lower numbers of seals in more places), is unknown but appears unrelated to changes in sea ice conditions. We analyzed both historic and satellite‐derived ice data confirming a large expansion of pack ice mostly offshore of the Ross Sea, and not over the continental shelf (main Weddell seal habitat), and a thinning of fast ice along Victoria Land (conceivably beneficial to seals). Timing of fast ice presence and extent in coves and bays along Victoria Land, remains the same. The reduction in numbers is consistent with an altered food web, the reasons for which are complex. In the context of a recent industrial fishery targeting a seal prey species, a large‐scale seal monitoring program is required to increase understanding of seal population changes.     

Relocation or duplication of the helix A sequence of T4 lysozyme causes only modest changes in structure but can increase or decrease the rate of folding

In T4 lysozyme, helix A is located at the amino terminus of the sequence but is associated with the C-terminal domain in the folded structure. To investigate the implications of this arrangement for the folding of the protein, we first created a circularly permuted variant with a new amino terminus at residue 12. In effect, this moves the sequence corresponding to helix A from the N- to the C-terminus of the molecule. The protein crystallized nonisomorphously with the wild type but has a very similar structure, showing that the unit consisting of helix A and the C-terminal domain can be reconstituted from a contiguous polypeptide chain. The protein is less stable than the wild type but folds slightly faster. We then produced a second variant in which the helix A sequence was appended at the C-terminus (as in the first variant), but was also restored at the N-terminus (as in the wild type). This variant has two helix A sequences, one at the N-terminus and the other at the C-terminus, each of which can compete for the same site in the folded protein. The crystal structure shows that it is the N-terminal sequence that folds in a manner similar to that of the wild type, whereas the copy at the C-terminus is forced to loop out. The stability of this protein is much closer to that of the wild type, but its rate of folding is significantly slower. The reduction in rate is attributed to the presence of the two identical sequence segments which compete for a single, mutually exclusive, site.     

The decrease of catalase or esterase D activity in patients with microdeletions of 11p or 13q does not increase their radiosensitivity

Lymphocyte cultures from patients affected by retinoblastoma (Rb), with or without a microdeletion of chromosome 13, and Wilms tumor (WT), with a microdeletion of chromosome 11p where exposed to gamma-ray radiation during S and G2 phases. Chromatid and chromosome lesions were scored and compared to those observed in controls. No significant differences were detected, neither between patients and controls, nor between patients carrying or not a microdeletion. This lack of difference was unexpected since the genes for catalase and esterase D, also called S-formyl glutathione hydrolase, which are two detoxication enzymes, are deleted in case of microdeletion of 11p and 13q, respectively.     

The fitting of the logistic equation to the rate of increase of population density

Though there are many problems on the usefulness of the logistic curve, it may be necessary to examine before discussing these problems whether or not the actual data fit to the theoretical values. It has been clarified in this paper that the relation between the population density and its rate of increase per individual described by the differential equation (1) is represented by a straight line on a finite difference diagram on which N_i+1−N_i/N_i values are plotted against N_i+1. Utilizing this linear relation we may examine the fittness of the logistic curve to the actual data and when it is fitted we may estimate the parameters of the logistic equation by (5) and (6). The result of the application of this method to the experimental populations of azuki bean weevil indicates that the relation between parent and progeny densities fits well to the logistic type as has been proved byFujita andUtida (1953) who utilized the linear reltion between 1/R+2σ and parent density where R is the apparent rate of reproduction and σ is a constant dependent primarily upon the length of adult life (0≦σ≦1).     

Blockade of AMPA/kainate receptors can either decrease or increase the survival of cultured neocortical cells depending on the stage of maturation

Neurotoxicity has often been associated with glutamate receptor stimulation and neuroprotection with glutamate receptor blockade. However, the relationship may be much more complex. We dissociated cells from the rat neocortical anlage at an early stage of prenatal development (embryonic day 14). The cells were exposed in vitro to agonists and antagonists of alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate (AMPA)/kainate and N-methyl-D-aspartate (NMDA) receptors and the effects on differentiation and survival have been quantitatively and qualitatively evaluated. NMDA and the non-competitive antagonist (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]-cyclohepten-5,10-imine hydrogen maleate (MK-801) had the expected effects (the agonist decreasing and the antagonist increasing neuronal survival) when applied at a relatively advanced stage of in vitro maturation, but no significant effect in either direction at earlier stages. Kainate also had an effect on cell survival only at an advanced stage (where it decreased the number of cells). However, this cannot be attributed to the absence of functional AMPA/kainate receptors at earlier stages, since: (1) cells could be loaded with cobalt; and (2) early application of kainate dramatically reduced the number of cobalt-positive cells. Furthermore, exposure at early stages to 6,7-dinitroquinoxaline-2,3-dione (DNQX), or GYKI 53655, (competitive and non-competitive AMPA receptor antagonists, respectively) strongly reduced cell survival. The effects were concentration- and time-dependent with a complex time--curve. The decrease in cell number was maximal after antagonist application from 2 to 5 days in vitro. The effects of DNQX could be cancelled by co-application of kainate. When exposed to an antagonist at later stages of development, the number of surviving cells gradually approached control values and finally became significantly higher. Our results suggest that cells of the developing neocortex (and perhaps newly generated cells in the adult brain) require at different stages of their development, an appropriate level of AMPA/kainate receptor activation.     

The selective increase or decrease of organellar DNA in generative cells just after pollen mitosis one controls cytoplasmic inheritance

Organellar DNA in mature pollen grains of eight angiosperm species (Actinidia deliciosa Lindl., Antirrhinum majus L., Arabidopsis thaliana (L.) Heynh., Medicago sativa L., Musa acuminata Colla, Pelargonium zonale (L.) L'Hér, Petunia hybrida Vilm. and Rhododendron mucronatum (Blume) G. Don, in which the modes of organellar inheritance have been determined genetically, was observed by fluorescence microscopy using Technovit 7100 resin sections double-stained with 4′,6-diamidino-2-phenylindole (DAPI) and 3,3′-dihexyloxacarbocyanine iodide (DiOC₆). The eight species were classified into four types, based on the presence or absence of organellar DNA in mature generative cells: namely (1) type “m+p+”, which has both mitochondrial and plastid DNA (P. zonale), (2) type “m+p–”, which only has mitochondrial DNA (M. acuminata), (3) type “m−p+”, which only has plastid DNA (A. deliciosa, M. sativa, R. mucronatum), and (4) type “m−p−”, which has neither mitochondrial nor plastid DNA (A. majus, A. thaliana, P. hybrida). This classification corresponded to the mode of organellar inheritance determined by genetic analysis. The presence or absence of mitochondrial and plastid DNA corresponded to paternal/biparental inheritance or maternal inheritance of the respective organelle, respectively. When organellar DNA was present in mature generative cells (m+ or p+), the DNA content of the organelles in the generative cells started to increase immediately after pollen mitosis one (PMI). In contrast, the DNA content of organelles in generative cells decreased rapidly after PMI when organellar DNA was absent from mature generative cells (m− or p−). These results indicate that the modes of inheritance (paternal/biparental inheritance or maternal inheritance) of mitochondria and plastids are determined independently of each other in young generative cells just after PMI. Received: 22 December 1998 / Accepted: 8 February 1999