An autonomous cell-cycle oscillator involved in the coordination of G1 events

In early embryonic development, the cell cycle is paced by a biochemical oscillator involving cyclins and cyclin-dependent kinases (cdks). Essentially the same machinery operates in all eukaryotic cells, although after the first few divisions various braking mechanisms (the so-called checkpoints) become significant. Haase and Reed have recently shown that yeast cells have a second, independent oscillator which coordinates some of the events of the G1 phase of the cell cycle.(1) Although the biochemical nature of this oscillator is not known,it seems unlikely to be a redundant cyclin/cdk system. BioEssays 22:3-5, 2000.     

31P magnetic resonance spectroscopy study of phosphocreatine recovery kinetics in skeletal muscle: the issue of intersubject variability

We have analyzed by (31)P MRS the relationship between kinetic parameters of phosphocreatine (PCr) recovery and end-of-exercise status under conditions of moderate and large acidosis induced by dynamic exercise. Thirteen healthy subjects performed muscular contractions at 0.47 Hz (low frequency, moderate exercise) and 0.85 Hz (high frequency, heavy exercise). The rate constant of PCr resynthesis (k(PCr)) varied greatly among subjects (variation coefficients: 43 vs. 57% for LF vs. HF exercises) and protocols (k(PCr) values: 1.3+/-0.5 min(-1) vs. 0.9+/-0.5 min(-1) for LF vs. HF exercises, P<0.03). The large intersubject variability can be captured into a linear relationship between k(PCr), the amount of PCr consumed ([PCr(2)]) and pH reached at the end of exercise (pH(end)) (k(PCr)=-3.3+0.7 pH(end)-0.03 [PCr(2)]; P=0.0007; r=0.61). This dual relationship illustrates that mitochondrial activity is affected by end-of-exercise metabolic status and allows reliable comparisons between control, diseased and trained muscles. In contrast to k(PCr), the initial rate of PCr recovery and the maximum oxidative capacity were always constant whatever the metabolic conditions of end-of-exercise and can then be additionally used in the identification of dysfunctions in the oxidative metabolic pathway.     

Effect of concentrate percentage on ruminal pH and time-budget in dairy goats

The aim of this study was to compare rumen pH and time-budget in eight mid-lactation goats receiving two diets in a cross-over design (low-concentrate diet (L): 30% and high-concentrate diet (H): 60% concentrate). Feeding H increased daily intake (4.3 ± 0.08% v. 4.7 ± 0.08% of body weight for L and H, respectively) and daily milk production (3.01 ± 0.130 v. 3.50 ± 0.130 kg/day of 3.5% fat-corrected milk for L and H, respectively). It decreased milk fat and inverted the fat-to-protein ratio (1.07 ± 0.054 v. 0.94 ± 0.054 for L and H, respectively). As suggested by the percentage of time spent with rumen pH below 6.0 (23.4 ± 6.60% v. 39.9 ± 5.88% for L and H, respectively), H was more acidogenic than L. When offered H instead of L, goats spent less time eating (298 ± 17.5 v. 265 ± 17.5 min for L and H, respectively) and ruminating (521 ± 21.0 v. 421 ± 21.0 min for L and H, respectively) but more time resting (352 ± 27.1 v. 459 ± 21.1 min for L and H, respectively) over a 24-h period. They also tended to spend more time drinking (20 ± 2.9 v. 25 ± 2.9 min for L and H, respectively; P = 0.08) when offered H rather than L. These differences in activities were mainly observed during the first hours following feeding. When offered H, goats adapted their feeding behaviour around the feedings, which allowed them to limit the physiological disturbances potentially inducible by H and to increase milk production, without experiencing too much acidosis.     

Risk factors for new intramammary infections during the dry period in untreated dairy cows from herds using selective dry cow therapy

This study aimed at investigating risk factors for new intramammary infections (IMI) during the dry period in untreated cows from herds using selective dry cow antibiotic therapy (DCT). A total of 980 uninfected quarters in 347 untreated cows from 28 herds using selective DCT were included in a prospective survey. A herd-level questionnaire and an individual cow-level recording sheet were implemented to collect data on putative risk factors. Quarter milk samples were taken at drying-off and on day 3 after calving to assess the occurrence of new IMI during the dry period. A multivariate model including a herd effect as random and a cow effect as repeated was run at the quarter level. Interactions between risk factors and the cow infection status at drying-off (cow infected in at least one quarter v. uninfected) were checked. Three risk factors were found significantly associated with the risk for new IMI without interaction (P < 0.05): cows infected in at least one quarter at drying-off (v. uninfected cows) (relative risks (RR) = 1.58); long preceding lactation (>355 days v. shorter length) (RR = 1.62); long dry period (>65 days v. shorter length) (RR = 1.46). One risk factor acted only in interaction with the cow infection status at drying-off: in cows uninfected at drying-off, the risk for new IMI was significantly higher in cows with short teats (RR = 1.21) when compared with cows with long or normal teats, while the reverse relationship was observed in cows infected at drying-off. Risk factors can be translated in recommendations, for instance to have dry periods not longer than 2 months. Moreover, as suggested by our results, the efficacy of selective DCT towards the prevention of new IMI would be improved if all infected cows were detected and treated. Criteria to accurately identify these infected cows should be therefore further investigated.     

Increased lipid peroxidation in pregnant women after iron and vitamin C supplementation

Iron overload could promote the generation of free radicals and result in deleterious cellular damages. A physiological increase of oxidative stress has been observed in pregnancy. A routine iron supplement, especially a combined iron and vitamin C supplementation, without biological justifications (low hemoglobin [Hb] and iron stores) could therefore aggravate this oxidative risk. We investigated the effect of a daily combined iron supplementation (100 mg/d as fumarate) and vitamin C (500 mg/d as ascorbate) for the third trimester of pregnancy on lipid peroxidation (plasma TBARS), antioxidant micronutriments (Zn, Se, retinol, vitaminE, (β-carotene) and antioxidant metalloenzymes (RBC Cu-Zn SOD and Se-GPX). The iron-supplemented group (n=27) was compared to a control group (n=27), age and number of pregnancies matched. At delivery, all the women exhibited normal Hb and ferritin values. In the supplemented group, plasma iron level was higher than in the control group (26.90±5.52 mmol/L) and TBARs plasma levels were significantly enhanced (p<0.05) (3.62±0.36 vs 3.01±0.37 mmol/L). No significant changes were observed in plasma trace elements and red blood cell antioxidant metalloenzymes. Furthermore, the α-tocopherol plasma level was lowered in the iron-supplemented groups, suggesting an increased utilization of vitamin E. These data show that pharmalogical doses of iron, associated with high vitamin C intakes, can result in uncontrolled lipid peroxidation. This is predictive of adverse effects for the mother and the fetus. This study illustrates the potential harmful effects of iron supplementation when prescribed only on the assumption of anemia and not on the bases of biological criteria.     

Usefulness of linked DNA probes for prenatal diagnosis of cystic fibrosis: report of a case in a 1:4 risk pregnancy

Prenatal diagnosis of cystic fibrosis was performed with linked DNA probes in a couple with a 1:4 risk. The limits and the future of molecular prenatal diagnosis are discussed.     

Chromatographic approach to study the configurational stability of Ni(II) complexes of amino‐acid Schiff bases possessing stereogenic nitrogen

Herein, we disclose the design of a model Ni(II) complex of glycine Schiff base possessing single‐nitrogen stereogenic center, which was successfully used for high‐performance liquid chromatography (HPLC)‐assisted assessment of its configurational stability. The major finding is that the configurational stability of the Ni(II)‐coordinated nitrogen is profoundly dependent on the reaction conditions used, in particular the solvent, and can range from inconsequential (t_½ less than 5 min) to virtually completely stable (t_½ 90 y). The discovery reported in this study most likely to be of certain theoretical and synthetic value.     

SSR allelic diversity changes in 480 European bread wheat varieties released from 1840 to 2000

A sample of 480 bread wheat varieties originating from 15 European geographical areas and released from 1840 to 2000 were analysed with a set of 39 microsatellite markers. The total number of alleles ranged from 4 to 40, with an average of 16.4 alleles per locus. When seven successive periods of release were considered, the total number of alleles was quite stable until the 1960s, from which time it regularly decreased. Clustering analysis on Neis distance matrix between these seven temporal groups showed a clear separation between groups of varieties registered before and after 1970. Analysis of qualitative variation over time in allelic composition of the accessions indicated that, on average, the more recent the European varieties, the more similar they were to each other. However, European accessions appear to be more differentiated as a function of their geographical origin than of their registration period. On average, western European countries (France, The Netherlands, Great Britain, Belgium) displayed a lower number of alleles than southeastern European countries (former Yugoslavia, Greece, Bulgaria, Romania, Hungary) and than the Mediterranean area (Italy, Spain and Portugal), which had a higher number. A hierarchical tree on Neis distance matrix between the 15 geographical groups of accessions exhibited clear opposition between the geographical areas north and south of the arc formed by the Alps and the Carpathian mountains. These results suggest that diversity in European wheat accessions is not randomly distributed but can be explained both by temporal and geographical variation trends linked to breeding practices and agriculture policies in different countries.Electronic Supplementary Material Supplementary material is available for this article at     

Transduction of human colony-stimulating factor-1 (CSF-1) receptor into interleukin-3-dependent mouse myeloid cells induces both CSF-1-dependent and factor-independent growth.

A retroviral vector encoding the receptor for human colony-stimulating factor-1 (CSF-1) was introduced into murine myeloid FDC-P1 cells which require interleukin-3 (IL-3) for their proliferation and survival in culture. Cells expressing the CSF-1 receptor (CSF-1R), selected by fluorescence-activated cell sorting in the continued presence of murine IL-3, formed colonies in semisolid medium and were able to proliferate continuously in liquid cultures containing human recombinant CSF-1. Thus, although they do not synthesize endogenous murine CSF-1R, FDC-P1 cells express the downstream components of the CSF-1 mitogenic pathway necessary for its signal-response coupling. After receptor transduction, slowly proliferating factor-independent variants that produced neither CSF-1 nor growth factors able to support the proliferation of parental FDC-P1 cells also arose. When the human CSF-1R was expressed in FDC-P1 cells under the control of an inducible metallothionein promoter, the frequencies of both CSF-1-responsive and factor-independent variants increased after heavy-metal treatment. In addition, a monoclonal antibody to human CSF-1R arrested colony formation by both the CSF-1-dependent and factor-independent cells but did not affect their growth in response to IL-3. Therefore, the induction of both the CSF-1-dependent and factor-independent phenotypes depended on expression of the transduced human CSF-1R.     

Biomass and photosynthesis of size-fractionated phytoplankton in Canadian Shield lakes

Both in situ primary production and biomass (chlorophyll ) of fractionated phytoplankton (<64,µ, <25 µm and < 10 µm) were studied in 10 Canadian Shield lakes to elucidate the spatial and temporal variability of the contribution of size fractions to the biomass and primary production of the phytoplankton community. Mean summer biomass and production of each size fraction varied significantly between lakes. Within lakes, temporal variation was low for biomass but great for production. However, temporal variation can be considered of minor importance during the sampling period, as compared to the spatial variation between lakes. Algae from the < 10 µm size fraction were the most important in biomass (41–65 %) and production (23–69%). The temporal trends for both phytoplankton variables thus generally followed closely that of the < 10 µm size fraction. Among the physical, chemical and morphometric variables of the studied lakes, water transparency (Secchi disk), total phosphorus, lake volume, lake area, and mean depth gave the best correlations with phytoplankton variables.Contribution number 354 from the Groupe de recherches en Ecologie des Eaux douces, Limnological Research Group, Université de Montréal.