Identification of a population of cells with hematopoietic stem cell properties in mouse aorta-gonad-mesonephros cultures

The aorta-gonad-mesonephros (AGM) region is a primary source of definitive hematopoietic cells in the midgestation mouse embryo. In cultures of dispersed AGM regions, adherent cells containing endothelial cells are observed first, and then non-adherent hematopoietic cells are produced. Here we report on the characterization of hematopoietic cells that emerge in the AGM culture. Based on the expression profiles of CD45 and c-Kit, we defined three cell populations: CD45(low) c-Kit(+) cells that had the ability to form hematopoietic cell colonies in methylcellulose media and in co-cultures with stromal cells; CD45(low) c-Kit(-) cells that showed a granulocyte morphology; CD45(high) c-Kit(low/-) that exhibited a macrophage morphology. In co-cultures of OP9 stromal cells and freshly prepared AGM cultures, CD45(low) c-Kit(+) cells from the AGM culture had the abilities to reproduce CD45(low) c-Kit(+) cells and differentiate into CD45(low) c-Kit(-) and CD45(high) c-Kit(low/-) cells, whereas CD45(low) c-Kit(-) and CD45(high) c-Kit(low/-) did not produce CD45(low) c-Kit(+) cells. Furthermore, CD45(low) c-Kit(+) cells displayed a long-term repopulating activity in adult hematopoietic tissue when transplanted into the liver of irradiated newborn mice. These results indicate that CD45(low) c-Kit(+) cells from the AGM culture have the potential to reconstitute multi-lineage hematopoietic cells.     

The advantages of being evergreen

Recent research shows that the dominance of evergreen species in nutrient-poor environments can be explained by their low nutrient loss rates. From this work It appears that the plant traits that are associated with low nutrient loss rates lead to low maximum-dry-matter production and to low rates of litter decomposition. This suggests a positive feedback between the evergreen habit and low nutrient availability. The growth characteristics of evergreens lead to a low responsiveness to environmental changes. As a result, global warming may lead to changes in the distribution of evergreens.     

Regulatory role of insulin in the degradation of low density lipoprotein by cultured human skin fibroblasts.

The degradation of 125I-labeled low density lipoprotein by cultured human skin fibroblasts was enhanced 25% by preincubation of cells with insulin. This effect of insulin appeared to be mediated via stimulation of low density lipoprotein binding to its cell surface receptor, since binding and subsequent internalization of low density lipoprotein were stimulated to a similar extent as was degradation. In addition, insulin enhanced binding of low density lipoprotein at 4 degrees C, at which temperature internalization of the lipoprotein does not occur. A similar effect of insulin on the interaction of very low density lipoprotein with cultured fibroblasts was observed. Insulin-induced changes in the degradation of low density lipoprotein and very low density lipoprotein appeared to be a function of the change in lipoprotein binding. Thus, insulin may play a role in the regulation of low density lipoprotein and very low density lipoprotein degradation by peripheral cells by influencing the receptor-mediated transport of these lipoproteins.     

Interaction between maternal smoking and malnutrition in infant risk of gastroschisis

BACKGROUND: Gastroschisis is a severe birth defect characterized by a tear in the infant's abdominal wall. Young mothers have the highest risk of having an infant with gastroschisis. In an animal model, the defect resulted from exposure of pregnant mice to carbon monoxide (CO) in combination with a low protein and low zinc diet. METHODS: We evaluated this model in a study of 55 infants with gastroschisis and 94 age-matched controls that included maternal interview with a food frequency questionnaire. Smoking cigarettes (> or = 1 pack/day) or marijuana (more than once) 3 months prior to pregnancy indicated CO exposure. Low protein or zinc intake and a low body mass index (BMI) indicated maternal malnutrition. RESULTS: When assessed separately, high CO, low protein, low zinc, and low BMI were each significantly associated with an increased risk of gastroschisis. Although we observed significant CO-BMI and CO-zinc interactions after adjusting for income, only a combination of high CO exposure and low BMI yielded a synergistic adverse effect. Compared to the low risk of having an infant with gastroschisis for mothers who did not have low BMI and did not smoke, the risk of having an infant with gastroschisis was 16.3 times (95% CI, 2.49-113.4) higher for mothers who did not have low BMI but smoked, and 19.7 times (95% CI, 4.33-89.6) higher for mothers who did not smoke but had low BMI. However, the risk was 26.5 times (95% CI, 7.85-89.4) higher for mothers who had low BMI and smoked. CONCLUSIONS: Our results suggest that young mothers are at increased risk of having an infant with gastroschisis if they smoke and are also malnourished.     

低价林早期诊断: 生态因子途径

提出了低价林早期诊断的新思路,即根据低价林的形成规律,在林分还未表现出低价林状况时就能诊断出其发展趋势,以便及时采取相应的经营管理措施,以辽西油松林为例,从生态因子途径开展了低价林的早期诊断研究,建立了基于单因素实验和判别分析的生态因子途径早期诊断技术。研究表明,土层厚度X1,有机质含量X2,土壤全氮含量X3,土壤含水率X4,土壤微生物总数量X5可选择作为油松低价林早期诊断的敏感指标;在综合诊断时引入了判别分析的数量分类方法,并根据判别分析的思路建立了油松林生长状况生态因子途径早期诊断方法,其步骤：1）确定判别指标;2）建立判别函数Y＝1．596X1－0．51X2－3．196X3＋1．622X4＋1．898X5;3）通过判别函数和研究对象的各项判别指标值进行早期诊断低价林早期诊断的技术与方法尚有待进一步地研究,检验和完善。     

Metabolism of lipoproteins in nonhuman primates. Studies on the origin of low density lipoprotein apoprotein in the plasma of the squirrel monkey.

The plasma of squirrel monkeys contains extremely low levels of very low density lipoproteins. The delipidated apoproteins from the different lipoprotein density classes of this species show a heterogeneity similar to that of man and the rat. The biosynthesis of the apoproteins of squirrel monkey lipoproteins was studied in fasted normal and Triton WR1339-treated animals. After intravenous injection of [3-H] leucine, maximal labeling of very low density lipoproteins occurred after 1 h, intermediate density lipoproteins (d 1.006--1.019) in 2 h, and low density lipoproteins after 3 h. At all times, however, low density lipoproteins had the greatest percentage of radioactivity. Polyacrylamide gel electrophoresis revealed that the apoprotein B moiety of very low density and intermediate density lipoproteins contained 62% and 81% of the total radioactivity in these lipoproteins whereas the fast-migrating peptides were minimally labeled. In monkeys injected with Triton WR1339, 70--80% of the radioactivity incorporated into d smaller than 1.063 lipoproteins was in very low density lipoproteins with only 10--15% in intermediate and low density lipoproteins. After injection of 3-H-labeled very low density lipoproteins and [14-C] leucine into Triton-treated monkeys, catabolism of 3-H-labeled very low density lipoprotein to intermediate and low density lipoproteins was small and was significantly less than corresponding values for the incorporation of [14-C] leucine. Thus, breakdown of very low density lipoproteins could not account for all the labeled apoprotein B present in the intermediate and low density lipoprotein fractions. The results indicate that most, but not all, of the newly synthesized apoprotein B enters plasma in very low density lipoproteins and that the low concentrations of this lipoprotein in squirrel monkey plasma are a consequence of its rapid turnover.     

Low cost of locomotion in lizards that are active at low temperatures

The nocturnality hypothesis of K. Autumn and coworkers states that nocturnal geckos have evolved a low energetic cost of locomotion (C(min)). A low C(min) increases maximum aerobic speed and partially offsets the decrease in maximum oxygen consumption caused by activity at low nocturnal temperatures. We tested whether a low C(min) is unique to nocturnal geckos or represents a more general pattern of convergent evolution among lizards that enables nocturnality and/or cold-temperature activity. We measured C(min) in four carefully selected lizard species from New Zealand (two nocturnal and two diurnal; n=5-9 individuals per species), including a nocturnal and diurnal gecko (a low C(min) is a gecko trait and is not related to nocturnality), a nocturnal skink (a low C(min) is related to being nocturnal), and a diurnal skink active at low temperatures (a low C(min) is related to being active at low body temperatures). The C(min) values of the four species measured in this study (range=0.21-2.00 mL O(2) g(-1) km(-1)) are lower than those of diurnal lizards from elsewhere, and the values are within or below the 95% confidence limits previously published for nocturnal geckos. A low C(min) increases the range of locomotor speeds possible at low temperatures and provides an advantage for lizards active at these temperatures. We accepted the hypothesis that nocturnal lizards in general have a low C(min) and provide evidence for a low C(min) in lizards from cool-temperate environments. The low C(min) in lizards living at high latitudes may enable extension of their latitudinal range into otherwise thermally suboptimal habitats.     

Relationship of low lean body mass with body weight increase until one year of age and current lifestyles in Japanese young women

To investigate factors affecting the low lean body mass (LBM) of young women, we focused on the increase in body weight until one year of age and current lifestyles. In 442 young women, the increase in body weight from birth until one year of age, breast-feeding method in infancy, current physique index and body composition, and physique and lifestyles were investigated using a questionnaire. Subjects with an LBM percentile of less than 33.3 (less than 36.8 kg) were classified as having a low LBM (n = 150), and those with a 33.3 or higher LBM percentile as the control (n = 293). Based on body weight changes from birth to days 3 and 7, the subjects were divided into a rapid weight gain group and two non-rapid weight gain groups (groups 1-3). To analyze factors involved in a low LBM, multivariate analysis using a logistic model was employed. The prevalence of a low LBM in the rapid weight gain group was 0.41 times higher than in the others. The prevalence of a low LBM with a low birth weight was 0.58 times higher, indicating that a low birth weight is likely to result in a low LBM. Regarding the lifestyles, the prevalence of a low LBM in subjects with a current breakfasting habit was 0.60 times higher than in those without one. These findings suggest that the thinness of young women characterized by a low LBM is associated with the increase in body weight until one year of age and current lifestyles.     

Secondarily diurnal geckos return to cost of locomotion typical of diurnal lizards

Previous studies showed that nocturnal geckos evolved a low energetic cost of locomotion (Cmin), which increases maximum aerobic speed and partially offsets the decrease in maximal oxygen consumption caused by activity at low nocturnal temperatures. Because the advantage of a low Cmin should apply at high diurnal temperatures as well as at low nocturnal temperatures, I hypothesized that Cmin remained low in geckos that have secondarily evolved diurnality. I measured Cmin in two secondarily diurnal gecko species, Rhoptropus bradfieldi (4.7 g+/-0.71 SE) and Phelsuma madagascariensis (23.9 g+/-3.7 SE), during steady exercise on a treadmill and rejected the hypothesis that secondarily diurnal geckos retain the low Cmin of their nocturnal ancestors. The Cmin in R. bradfieldi (2.468 mL O2 g-1 km-1+/-0.489 SE) and P. madagascariensis (1.389 mL O2 g-1 km-1+/-0.119 SE) returned to values typical of ancestrally diurnal lizards. This suggests that there is a trade-off that outweighs the performance advantage of low Cmin in a diurnal environment and that may cause an evolutionary association between Cmin and activity time (diurnality/nocturnality).     

The effect of ethanol on the lipoprotein metabolism of aortic smooth muscle cells

The effect of ethanol exposure on the binding and metabolism of bovine low density lipoprotein by bovine arterial smooth muscle cells was studied. In cells exposed to ethanol (80 mM) for 48 hr or 14 days and incubated with low density lipoprotein for 24 hr there was a reduction in the amount of low density lipoprotein internalised at all concentrations of lipoprotein. There was no effect on the rate of degradation of the low density lipoprotein and no demonstrable changes in the amount of low density lipoprotein bound to the cell surface at high concentrations of low density lipoprotein. Similar results for internalisation and degradation were obtained in a time dependent study. Binding was shown to be reduced in the ethanol treated cells (48 hr) when low concentrations (5 micrograms/ml) of low density lipoprotein were incubated for short periods (less than 3 hr). Scatchard plot analysis indicated that this reduced binding may be due to a reduction of receptor numbers in these cells.     

低压环境中植物的生长特性及适应机理研究进展

在低压受控生态生命保障系统中, 植物是关键的生物部件。在低压环境中, 植物会面临与常压不同的总大气压力(总压)、O₂分压和CO₂分压等大气环境条件。虽然植物在一定的低压环境中能完成完整的生长周期(从种子到种子), 但为了适应新的大气环境条件, 其生理生态特性均会发生改变。该文综述了低压对植物种子萌发、植株形态结构、生长特性、根系养分吸收、植株营养品质、叶片气体交换和乙烯(C₂H₄)释放的影响, 以及低压环境诱导的植物基因表达和相应的调控机理等, 从不同角度阐述了低压环境对植物生长的影响及植物对低压环境的适应机理, 并指出了将来需要进一步开展的试验研究方向。     

Evidence for the appearance of an uncoupled form of the beta-adrenergic receptor distinct from the internalized receptor

Agonist treatment of C6-glioma cells induces two altered states in beta-adrenergic receptors, a low affinity for the hydrophilic antagonist CGP-12177 and a low affinity for agonists like isoproterenol. We present evidence that, in cells not treated to inhibit receptor internalization, the two properties occur with a different time course, the low affinity for isoproterenol preceding that for CGP-12177. In that the low affinity for CGP-12177 is due to the internalization of the receptor, the results indicate that uncoupling of the receptor, indicated by the low affinity for isoproterenol, occurs while the receptor is still located on the cell surface. Removal of the agonist leads to reappearance of the receptor to the plasma membrane followed by loss of the uncoupled state.     

Patterns and Predictors of Language and Literacy Abilities 4-10 Years in the Longitudinal Study of Australian Children

Aims

Oral language is the foundation of literacy. Naturally, policies and practices to promote children’s literacy begin in early childhood and have a strong focus on developing children’s oral language, especially for children with known risk factors for low language ability. The underlying assumption is that children’s progress along the oral to literate continuum is stable and predictable, such that low language ability foretells low literacy ability. This study investigated patterns and predictors of children’s oral language and literacy abilities at 4, 6, 8 and 10 years. The study sample comprised 2,316 to 2,792 children from the first nationally representative Longitudinal Study of Australian Children (LSAC). Six developmental patterns were observed, a stable middle-high pattern, a stable low pattern, an improving pattern, a declining pattern, a fluctuating low pattern, and a fluctuating middle-high pattern. Most children (69%) fit a stable middle-high pattern. By contrast, less than 1% of children fit a stable low pattern. These results challenged the view that children’s progress along the oral to literate continuum is stable and predictable.

Findings

Multivariate logistic regression was used to investigate risks for low literacy ability at 10 years and sensitivity-specificity analysis was used to examine the predictive utility of the multivariate model. Predictors were modelled as risk variables with the lowest level of risk as the reference category. In the multivariate model, substantial risks for low literacy ability at 10 years, in order of descending magnitude, were: low school readiness, Aboriginal and/or Torres Strait Islander status and low language ability at 8 years. Moderate risks were high temperamental reactivity, low language ability at 4 years, and low language ability at 6 years. The following risk factors were not statistically significant in the multivariate model: Low maternal consistency, low family income, health care card, child not read to at home, maternal smoking, maternal education, family structure, temperamental persistence, and socio-economic area disadvantage. The results of the sensitivity-specificity analysis showed that a well-fitted multivariate model featuring risks of substantive magnitude did not do particularly well in predicting low literacy ability at 10 years.     

Stimulation of 25-hydroxyvitamin D3-1alpha-hydroxylase by phosphate depletion.

The ability of low phosphorus diets to stimulate the activity of the 25-hydroxyvitamin D3-1alpha-hydroxylase was tested in the chick. Feeding low phosphorus diets for 2 weeks resulted in a marked increase in enzyme activity relative to chicks fed a normal phosphorus diet. Stimulation of the 25-hydroxyvitamin D3-1alpha-hydroxylase activity by low phosphorus diets, however, was not as great as that observed with a low calcium diet. The low phosphorus and low calcium diets probably results from increased 1,25-dihydroxyvitamin D3 synthesis, whereas the stimulation by phosphate deprivation is only partly the result of increased 1,25-dihydroxyvitamin D3 production.     

The effect of daily exposure to low hardening temperature on plant vital activity

Phenomenological responses of plants to daily short-term exposure to low hardening temperature was studied under chamber and field conditions. Experiments were carried out on cucumber (Cucumis sativus L.), barley (Hordeum vulgare L.), marigolds (Tagetes L.), and petunia (Petunia × hybrida) plants. The obtained data demonstrated a similar pattern of response in all studied plant species to different variants of exposure to low hardening temperature. The main features of plant response to daily short-term exposure to low hardening temperature include: a higher increment in cold tolerance (cf. two-or threefold increase relative to constant low hardening temperature) that peaked on day 5 (cf. day 2 at constant low hardening temperature) and was maintained for 2 weeks (cf. 3–4 days at constant low hardening temperature); a simultaneous increase in heat tolerance (cf. twofold relative to constant low hardening temperature) maintained over a long period (cf. only in the beginning of the exposure to constant low hardening temperature); a sharp drop in the subsequent cold tolerance after plant incubation in the dark (cf. a very low decrease in cold tolerance following the exposure to constant low hardening temperature); a combination of high cold tolerance and high photochemical activity of the photosynthetic apparatus (cf. a low non-photochemical quenching at constant low hardening temperature); and the capacity to increase cold tolerance in response to repeated short-term exposures to low hardening temperature in plants grown outdoors (cf. a gradual increase after repeated exposure to constant low hardening temperature). Possible mechanisms underlying the plant response to daily short-term exposure to low temperature are proposed.     

Mycobacterium tuberculosis DosR is Required for Activity of the PmbtB and PmbtI Promoters under Hypoxia

Mycobacterium tuberculosis has the ability to survive for extended periods of time under conditions of low oxygen, low pH, low iron and low nutrients. The mycobactins (M. tuberculosis siderophores) play a key role in scavenging iron from the environment and are induced in response to low iron in an IdeR-regulated manner. We demonstrate that the promoters of two mycobactin gene (mbt) operons are also expressed during adaptation to low oxygen, and that this expression is dependent on the DosR regulator. Up-regulation of mbt operons induced by low iron was not DosR-dependent. DosR is a member of a two component regulatory system which responds to oxygen availability. Deletion of the DosR regulator led to increased expression of bacterioferritin and increased capacity to grow under iron depletion. These data provide a link between the mycobacterial response to two conditions likely to be encountered in vivo, low iron and low oxygen.     

Synthesis and release of low density lipoproteins by the isolated perfused pig liver.

In previous studies, we have shown that a relatively large amount of low density lipoproteins is released into the perfusate during isolated pig liver perfusion. The present studies were done to determine the source of these lipoproteins. Breakdown of the very low density lipoproteins to low density lipoproteins by the perfusion apparatus or by hepatic catabolism was excluded by adding 125I very low density lipoproteins to the perfusate in the presence and absence of a liver and then measuring the radioactivity in the low density lipoprotein fraction after rate-zonal ultracentrifugation. Release of preformed low density, lipoproteins from the liver was investigated by injecting iodine-labeled low density lipoproteins in vivo several hours prior to perfusion of the liver and then measuring the release of labeled low density lipoproteins into the perfusate. It was shown that intact labeled low density lipoproteins were released by the perfused liver. De novo synthesis of the low density lipoproteins was established by measuring the incorporation of [1-14C]leucine into this lipoprotein fraction. The radioactivity in the low density lipoprotein fraction increased with time and accounted for 20 to 25% of the total radioactivity incorporated into all the lipoprotein fractions. The incorporation of [1-14C]leucine into the low density lipoproteins was confirmed by rate-zonal analysis. We conclude that the low density lipoproteins in the perfusate from pig liver perfusions were derived mainly from a preformed liver pool, but also partly from de novo synthesis by the liver.     

Effects of chemical combinations on the induction of aneuploidy in Saccharomyces cerevisiae

Nocodazole, ethyl acetate, acetone and methyl ethyl ketone all are known to induce aneuploidy. Treatment of yeast strain D61.M with mixtures containing ineffective low levels of nocodazole and ineffective low levels of these solvents was highly effective in inducing aneuploidy. Ineffective low levels of nocodazole mixed with ineffective low levels of methyl 2-benzimidazolecarbamate also gave elevated frequencies of aneuploidy. Dimethyl formamide, a solvent that does not induce aneuploidy, mixed with low levels of nocodazole gave no increase in aneuploidy frequency above those levels seen in controls.