An intron element modulating 5' splice site selection in the hnRNP A1 pre-mRNA interacts with hnRNP A1.

The hnRNP A1 pre-mRNA is alternatively spliced to yield the A1 and A1b mRNAs, which encode proteins differing in their ability to modulate 5' splice site selection. Sequencing a genomic portion of the murine A1 gene revealed that the intron separating exon 7 and the alternative exon 7B is highly conserved between mouse and human. In vitro splicing assays indicate that a conserved element (CE1) from the central portion of the intron shifts selection toward the distal donor site when positioned in between the 5' splice sites of exon 7 and 7B. In vivo, the CE1 element promotes exon 7B skipping. A 17-nucleotide sequence within CE1 (CE1a) is sufficient to activate the distal 5' splice site. RNase T1 protection/immunoprecipitation assays indicate that hnRNP A1 binds to CE1a, which contains the sequence UAGAGU, a close match to the reported optimal A1 binding site, UAGGGU. Replacing CE1a by different oligonucleotides carrying the sequence UAGAGU or UAGGGU maintains the preference for the distal 5' splice site. In contrast, mutations in the AUGAGU sequence activate the proximal 5' splice site. In support of a direct role of the A1-CE1 interaction in 5'-splice-site selection, we observed that the amplitude of the shift correlates with the efficiency of A1 binding. Whereas addition of SR proteins abrogates the effect of CE1, the presence of CE1 does not modify U1 snRNP binding to competing 5' splice sites, as judged by oligonucleotide-targeted RNase H protection assays. Our results suggest that hnRNP A1 modulates splice site selection on its own pre-mRNA without changing the binding of U1 snRNP to competing 5' splice sites.     

A histological and immunohistochemical study of the effects of N-acetyl cysteine on retinopathy of prematurity by modifying insulin-like growth factor-1

Retinopathy of prematurity (ROP) is a vasoproliferative disorder that occurs in premature infants and may lead to permanent visual impairment. We investigated both the possible protective role of N-acetyl cysteine (NAC) for preventing ROP and the role of IGF-1 in the disorder. Forty-five newborn rats were divided into three groups. Group 1 was raised in room air as controls. Group 2 was exposed to 60% oxygen for 14 days after birth, then transferred to room air. Group 3 was exposed to the same conditions as group 2, but received intraperitoneal injections of NAC on postnatal days 7–17. After 35 days, both eyes of all rats were processed for histology. Some sections were stained with hematoxylin and eosin to assess structural changes and other sections were immunostained to determine the location of IGF-1. Frozen sections also were prepared and stained for adenosine triphosphatase to detect retinal blood vessels. Compared to the controls, more blood vessels, many of which were abnormal, and increased IGF-1 expression were observed in group 2. In group 3, abnormal blood vessels and IGF-1 expression were less evident. NAC appeared to be an effective vascular-protective agent for ROP by decreasing IGF-1 expression.     

Electrocardiographic aspects of skin diving

Electrocardiographic (ECG) aspects of skin diving were monitored by means of continuous ECG recording in a pool 15 m deep. Ten regularly trained divers with different levels of experience divid a minimum of three consecutive times, holding their beath, reaching depths of 6 m, 9 m, and 12 or 15 m. The water temperature was 28 degrees C. During the ascending part of these dives, bradycardia was observed in all skin-divers. Minimal heart rate correlated negatively with the diver's experience (number of dives previously performed). In six divers cardiac arrhythmia was observed. Atrial arrhythmias were sometimes isolated occurrences, but more frequently they were multiple. Ventricular arrhythmias tended to be bigeminal. Apparently, forced expiration through the snorkel when surfacing precipitated these rhythmic disorders.     

Facteurs contrôlant la production primaire dens deux rivières soumises a une forte réduction de débit

The effects of river diversion on phytoplankton primary production and biomass in the downstream part of two rivers were studied in relation to physical and chemical variables. These rivers, situated north of the 52nd parallel, are characteristic of oligotrophic systems with phytoplankton primary production less than 10.76 mg C m^–2 h^–1, chlorophyll -a lower than 3.0 mg m^–3 and biomass between 118–1007 mg m^–3. The decrease in flow favored the establishment of an algal biomass approximately two times greater then that present before diversion. This increase in biomass was associated in one river with an increase of 2.5 times of the mean primary production. In the other river the primary production per unit of surface area remained stable but increased when expressed by unit volume, due to a great decrease in underwater light penetration, consequence of inorganic particular matter increase.

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Facteurs contrôlant la production primaire dens deux rivières soumises a une forte réduction de débit

     

Metabolic changes in the extracellular matrix during differentiation of myoblasts of the L6 line and of a Myo- non-fusing mutant

In the present study we have characterized by biochemical and immunochemical methods the changes which take place in collagen, laminin and fibronectin biosynthesis during the differentiation of clonal skeletal myoblasts of the L6 line. Time-course experiments showed that the relative rate of synthesis of collagen increased significantly during the cell-cell contact step of myogenesis and decreased later on. The major collagens synthesized were types I and III, found mainly as soluble precursors in the culture medium. Types IV and V collagens were detected exclusively in the cell layer. The relative amounts of types I and III collagens remained unchanged during myogenesis, while types IV and V collagens increased as the cells of the L6 line fused. In a non-fusing alpha-amanitin-resistant mutant of the L6 line (Ama 102), the rate of collagen synthesis was largely depressed and its rate of degradation was increased as compared with the fusing wild type. The synthesis of laminin was very low in cells of the fusing wild type, but abundant and associated with the cell layer of the Myo- mutant. The appearance of a muscle-specific extracellular matrix is a complex process involving changes in the organization, the biosynthesis and remodelling of its macromolecules of the extracellular matrix.     

PRESENCE OF ALGAE IN FRESHWATER ICE COVER OF FLUVIAL LAC SAINT‐PIERRE (ST. LAWRENCE RIVER,CANADA)1

Winter ice cover is a fundamental feature of north temperate aquatic systems and is associated with the least productive months of the year. Here we describe a previously unknown freshwater habitat for algal and microbial communities in the ice cover of the freshwater St. Lawrence River, Quebec, Canada. Sampling performed during winter 2005 revealed the presence of viable algal cells, such as Aulacoseira islandica (O. Müll.) Simonsen (Bacillariophyceae), and microbial assemblage growing in the ice and at the ice–water interface. Vertical channels (1–5 mm wide) containing algae were also observed. Concentrations of chl a ranged between 0.5 and 169 μg · L^?1 of melted ice, with maximal concentrations found in the lower part of the ice cores. These algae have the potential to survive when ice breakup occurs and reproduce rapidly in spring/summer conditions. Freshwater ice algae can thus contribute to in situ primary production, biodiversity, and annual carbon budget in various habitats of riverine communities.     

Conserved sequences in enzymes of the UDP-GlcNAc/MurNAc family are essential in hamster UDP-GlcNAc:dolichol-P GlcNAc-1-P transferase

The UDP-GlcNAc/MurNAc family of eukaryotic and prokaryotic enzymes use UDP-GlcNAc or UDP-MurNAc-pentapeptide as donors, dolichol-P or polyprenol-P as acceptors, and generate sugar-P-P-polyisoprenols. A series of six conserved sequences, designated A through F and ranging from 5 to 13 amino acid residues, has been identified in this family. To determine whether these conserved sequences are required for enzyme function, various mutations were examined in hamster UDP- GlcNAc:dolichol-P GlcNAc-1-P transferase (GPT). Scramble mutations of sequences B-F, generated by scrambling the residues within each sequence, demonstrated that each is important in GPT. While E and F scrambles appeared to prevent stable expression of GPT, scrambling of B- D resulted in GPT mutants that could be stably expressed and bound tunicamycin, but lacked enzymatic activity. Further, the C and D scramble mutants had an unexpected sorting defect. Replacement of sequences B-F with prokaryotic counterparts from either the B.subtilis mraY or E.coli rfe genes also affected GPT by preventing expression of the mutant protein (B, F) or inhibiting its enzymatic activity (C-E). For the C-E replacements, no acquisition of acceptor activity for polyprenol-P, the fully unsaturated natural bacterial acceptor, was detected. These studies show that the conserved sequences of the UDP- GlcNAc/MurNAc family are important, and that the eukaryotic and prokaryotic counterparts are not freely interchangeable. Since several mutants were efficiently expressed and bound tunicamycin, yet lacked enzymatic activity, the data are consistent with these sequences having a direct role in product formation.      

Ecological impacts of trees with modified lignin

Few experiments have yet been performed to explore the potential ecological impacts of genetic modification in long-lifespan species such as trees. In this paper, we review the available data on GM trees with modified lignin focussing on the results of the first long-term field trials of such trees. These trials evaluated poplars expressing antisense transgenes to reduce the expression of the lignin biosynthesis genes cinnamyl alcohol dehydrogenase (CAD) or caffeic acid/5-hydroxyferulic acid O-methyltransferase (COMT) with the aim of producing trees with improved pulping characteristics. The trees were grown for 4 years at two sites in France and England, and their ecological impacts and agronomic performance were assessed. Modifications to lignin in the poplars were maintained over the 4 years of the trial. The trees remained healthy throughout and growth was normal. The lignin modifications had no unexpected biological or ecological impacts. Interactions with leaf-feeding insects, microbial pathogens and soil organisms were unaltered although the short-term decomposition of transgenic roots was slightly enhanced. Investigation of the ecological impacts of the GM trees was curtailed by the early termination of the field trial when it was attacked and largely destroyed by anti-GM protestors. To supplement our work on the decomposition of GM plant materials with modified lignin, we have therefore turned to the study of transgenic tobacco lines where we can perform more comprehensive and controlled analyses of the biological and ecological effects of lignin-gene suppression.     

Quantification of angiogenesis in estrogen receptor-positive and negative breast carcinoma

Background

The objective of this study was to evaluate angiogenesis according to CD34 antigen expression in estrogen receptor (ER)-positive and negative breast carcinomas.

Methods

This study comprised 64 cases of infiltrating ductal carcinoma in postmenopausal women divided into two groups: Group A: ER-positive, n = 35; and Group B: ER-negative, n = 29. The anti-CD34 monoclonal antibody was used as a marker for endothelial cells. Microvessel count was carried out in 10 fields per slide using a 40× objective lens (magnification 400×). Statistical analysis of the data was performed using Student's t-test (p < 0.05).

Results

The mean number of vessels stained with the anti-CD34 antibody in the estrogen receptor-positive and negative tumors was 23.51 ± 1.15 and 40.24 ± 0.42, respectively. The number of microvessels was significantly greater in the estrogen receptor-negative tumors (p < 0.001).

Conclusion

ER-negative tumors have significantly greater CD34 antigen expression compared to ER-positive tumors.