Differentially regulated malate synthase genes participate in carbon and nitrogen metabolism of S. cerevisiae.

We have isolated a second gene (MLS1), which in addition to DAL7, encodes malate synthase from S. cerevisiae. Expression of the two genes is specific for their physiological roles in carbon and nitrogen metabolism. Expression of MLS1, which participates in the utilization of non-fermentable carbon sources, is sensitive to carbon catabolite repression, but nearly insensitive to nitrogen catabolite repression. DAL7, which participates in catabolism of the nitrogenous compound allantoin, is insensitive to carbon catabolite repression, but highly sensitive to nitrogen catabolite repression. Results obtained with null mutations in these genes suggest that S. cerevisiae contains at least one and perhaps two additional malate synthase genes.     

Aortic accumulation and plasma clearance of beta-VLDL and HDL: effects of diet-induced hypercholesterolemia in rabbits

To assess the role of beta-VLDL in diet-induced atherogenesis, the in vivo metabolism and aortic accumulation of 125I-labeled beta-VLDL were investigated in cholesterol-fed rabbits and chow-fed controls. 125I-labeled HDL and 125I-labeled albumin were studied for comparison. The fractional catabolic rate of 125I-labeled beta-VLDL was reduced in cholesterol-fed rabbits (0.011 vs 0.139 hr-1), but due to the high endogenous pool, the total beta-VLDL flux was very high (13.1 vs less than 1.1 mg/kg per 24 hr). These results suggest that elevated levels of beta-VLDL during cholesterol feeding were due to an enhanced rate of synthesis, a finding confirmed in hypercholesterolemic rabbits subjected to plasmapheresis. Following acute reduction of plasma cholesterol by plasmapheresis, the quantitative increases in beta-VLDL cholesterol concentrations (210 to 364 mg/dl) over the subsequent 24 hr were in agreement with the rise calculated from the plasma clearance kinetics of 125I-labeled beta-VLDL (378 mg/dl per 24 hr). Aortic accumulation of beta-VLDL in hypercholesterolemic rabbits was increased greater than 15-fold over controls. Accumulation was predominantly in the intimal atheromatous lesions. The fractional catabolic rate of 125I-labeled HDL was increased during cholesterol feeding (0.037 vs 0.021 hr-1). A decreased rate of synthesis appeared to be responsible for the markedly depleted plasma HDL. HDL accumulation within the aorta was attenuated greater than 9-fold in cholesterol-fed rabbits compared to those fed normal chow. Plasma kinetics and aortic accumulation of 125I-labeled albumin were similar in hypercholesterolemic and control rabbits.(ABSTRACT TRUNCATED AT 250 WORDS)     

Improving cross-cultural skills of medical students through medical school-community partnerships.

Postulating that a program integrating language skills with other aspects of cultural knowledge could assist in developing medical students'' ability to work in cross-cultural situations and that partnership with targeted communities was key to developing an effective program, a medical school and two organizations with strong community ties joined forces to develop a Spanish Language and Hispanic Cultural Competence Project. Medical student participants in the program improved their language skills and knowledge of cultural issues, and a partnership with community organizations provided context and resources to supplement more traditional modes of medical education.     

Tracing paternal ancestry in mice, using the Y-linked, sex-determining locus, Sry

The molecular evolution of mammalian Y-linked DNA sequences is of special interest because of their unique mode of inheritance: most Y- linked sequences are clonally inherited from father to son. Here we investigate the use of Y-linked sequences for phylogenetic inference. We describe a comparative analysis of a 515-bp region from the male sex- determining locus, Sry, in 22 murine rodents (subfamily Murinae, family Muridae), including representatives from nine species of Mus, and from two additional murine genera--Mastomys and Hylomyscus. Percent sequence divergence was < 0.01% for comparisons between populations within a species and was 0.19%-8.16% for comparisons between species. Our phylogenetic analysis of 12 murine taxa resulted in a single most- parsimonius tree that is highly concordant with phylogenies based on mitochondrial DNA and allozymes. A total evidence tree based on the combined data from Sry, mitochondrial DNA, and allozymes supports (1) the monophyly of the subgenus Mus, (2) its division into a Palearctic group (M. musculus, M. domesticus, M. spicilegus, M. Macedonicus, and M. spretus) and an Oriental group (M. cookii++, M. cervicolor, and M. caroli), and (3) sister-group relationships between M. spicilegus and M. macedonicus and between M. cookii and M. cervicolor. We argue that Y- chromosome DNA sequences represent a valuable new source of characters for phylogenetic inference.      

Le ionophore A23187

The acrosomic status of spermatozoa prepared for IVF has been evaluated by means of immunofluorescence test from Fenichel and Hsi using calcium A 23187 ionophore as inductor of acrosome reaction (AR). The spontaneous AR remains slight, even after 6 hour-incubation in Menezo B2 (6,8+2,7%). The response to ionophore, moderate before (11,2+9%), frankly increases after a 6h-capacitation (28,9+8,3%) in a group of 25 IVF couples (tubal indication, normal semen, positive fertilization). Nevertheless, it remains slight or null in 4 cases of unexplained repeated failure of fertilization. The response to ionophore A 23187 allows to explore the kinetics of capacitation of spermatozoa and their ability to perform AR. Its significance in terms of fecondance remains to be precised.     

Evolutionary optimization of fluorescent proteins for intracellular FRET

Fluorescent proteins that exhibit Forster resonance energy transfer (FRET) have made a strong impact as they enable measurement of molecular-scale distances through changes in fluorescence. FRET-based approaches have enabled otherwise intractable measurements of molecular concentrations, binding interactions and catalytic activity, but are limited by the dynamic range and sensitivity of the donor-acceptor pair. To address this problem, we applied a quantitative evolutionary strategy using fluorescence-activated cell sorting to optimize a cyan-yellow fluorescent protein pair for FRET. The resulting pair, CyPet-YPet, exhibited a 20-fold ratiometric FRET signal change, as compared to threefold for the parental pair. The optimized FRET pair enabled high-throughput flow cytometric screening of cells undergoing caspase-3-dependent apoptosis. The CyPet-YPet energy transfer pair provides substantially improved sensitivity and dynamic range for a broad range of molecular imaging and screening applications.     

Molecular organization and tissue-specific expression of an Arabidopsis 14-3-3 gene.

The 14-3-3 proteins, originally described as mammalian brain proteins, are ubiquitous in eukaryotes. We isolated an Arabidopsis 14-3-3 gene, designated GRF1-GF14 chi (for general regulatory factor1-G-box factor 14-3-3 homolog isoform chi), and characterized its expression within plant tissues. Sequence comparison of the GRF1-GF14 chi genomic clone with other 14-3-3 proteins demonstrated that the extreme conservation of 14-3-3 residues in several domains is encoded by the first three exons. The highly variable C-terminal domain is encoded by a divergent fourth exon that is unique among 14-3-3 homologs, suggesting that exon shuffling might confer gene-specific functions among the isoforms. The anatomical distribution and developmental expression of the Arabidopsis 14-3-3 protein were examined in transgenic plants carrying a GRF1-GF14 chi promoter-beta-glucuronidase construct. GF14 chi promoter activity was observed in the roots of both seedlings and mature plants. In immature flowers, GF14 chi promoter activity was localized to the buds. However, as the flowers matured, GF14 chi promoter activity was restricted to the stigma, anthers, and pollen. In immature siliques, GF14 chi promoter activity was initially localized to styles and abscission zones but was subsequently observed throughout mature siliques. In situ hybridization demonstrated that GF14 chi mRNA expression was prominent in epidermal tissue of roots, petals, and sepals of flower buds, papillae cells of flowers, siliques, and endosperm of immature seeds. Thus, plant 14-3-3 gene expression exhibits cell- and tissue-specific localization rivaling that observed for 14-3-3 proteins within the mammalian brain.     

Trophic ecology of parabiotic ants: Do the partners have similar food niches?

Organisms associated with another species may experience both costs and benefits from their partner. One of these costs is competition, which is the more likely if the two species are ecologically similar. Parabioses are associations between two ant species that share a nest and often attend the same food sources. Albeit parabioses are probably mutualistic, parabiotic partners may compete for food. We therefore investigated feeding niches and dietary overlap of two parabiotically associated ants in Borneo using cafeteria experiments and stable isotope analyses. The two species strongly differed in their food choices. While Crematogaster modiglianii mostly foraged at carbohydrate‐rich baits, Camponotus rufifemur preferred urea‐rich sources. Both species also consumed animal protein. The ¹⁵N concentration in Ca. rufifemur workers was consistently lower than in Cr. modiglianii. Camponotus rufifemur but not Cr. modiglianii possesses microbial endosymbionts, which can metabolize urea and synthesize essential amino acids. Its lower ¹⁵N signature may result from a relatively higher intake of plant‐based or otherwise ¹⁵N‐depleted nitrogen. Isotopic signatures of the two partners in the same parabiosis showed strongly parallel variation across nests. As we did not find evidence for spatial autocorrelation, this correlation suggests an overlap of food sources between the two ant species. Based on model simulations, we estimated a diet overlap of 22–66% for nitrogen sources and 45–74% for carbon sources. The overlap may arise from either joint exploitation of the same food sources or trophallactic exchange of food. This suggests an intense trophic interaction and potential for competition between the parabiotic partners.