Supra-normal susceptibility to acoustic trauma of the rat pup cochlea

1 Young and adult rats were exposed to a continuous 120 dB SPL white noise for 30 min. 2 Animals exposed before the 40th postnatal day showed drastic and permanent threshold shifts (PTS) at high frequencies (between 6 and 20 kHz). 3 After 60 days of age, only temporary threshold shifts (TTS) were noticed, which lasted 7 days. 4 Thus the sensory structures of the rat cochlea showed a supra-normal susceptibility to acoustic trauma, during and just after their anatomical differentiation. 5 These results support previous data obtained on hamsters and guinea-pigs and are discussed in terms of anatomo-functional relationships.     

Increase of ornithine decarboxylase activity elicited by reserpine in the peripheral and central monoaminergic systems of the rat

Ornithine decarboxylase activity was increased about tenfold in adrenal glands and in brain regions preponderantly containing aminergic neurons, by a single dose of 16 mol/kg of reserpine. Maximal enzyme activity in the adrenal glands was observed at about 8 hr after reserpine administration. The ornithine decarboxylase activity-time curves in the brain regions showed a concomitant polyphasic course, with the highest maximum at 12 hr postinjection. Ornithine decarboxylase induction is discussed as an early event in the cascade of molecular events preceding the induction of cell typic enzymes.     

Evidence for recombination in Candida glabrata

Despite its clinical importance, little is known of the epidemiology and population structure of Candida glabrata. C. glabrata possesses a mating type system similar to that in Saccharomyces cerevisiae, however mating, meiosis and recombination have not been demonstrated. We performed multilocus sequence typing on a collection of 165 isolates to test for evidence of genetic recombination. A total of 3345 bp from six loci (FKS, LEU2, NMT1, TRP1, UGP1, and URA3) were sequenced for each isolate. The polymorphisms at these loci defined 34 sequence types. Significant evidence for a clonal population was revealed by the index of association and the number of phylogenetically compatible pairs of loci. However, 14 examples of phylogenetic incompatibility were also found. Thus we conclude that although C. glabrata has a predominantly clonal population structure, the multiple phylogenetic incompatibilities found strongly suggest that recombination occurred during the evolution of C. glabrata, and may infrequently still occur.     

The use of a cell-cycle phase-marker may decrease the percentage of errors when using FISH in PGD

Fluorescent DNA probes are used to characterise the chromosome constitution of preimplantation embryos. FISH is used to select normal or balanced embryos in carriers of balanced chromosomal rearrangements, for embryo sexing or for aneuploidy screening in women of advanced age, who have had recurrent abortions or IVF failures. In most cases, FISH is performed on interphase blastomeres which are asynchronously dividing cells, that can be in G1, S or G2. However, a correct interpretation of a double FISH signal, which may correspond to a split signal, to a replicated chromosome region or to the presence of an extra chromosome is essential to establish an accurate diagnosis. To determine if the cell stage could influence the interpretation of FISH results, we compared the signal characteristics of one locus-specific probe, two different subtelomere region probes, and a centromere region probe in non-dividing Sertoli cells and in proliferating lymphocytes. Most cells had two signals per chromosome pair (i.e., a situation corresponding to G0 in Sertoli cells and to G1 or to a prereplication stage in lymphocytes). Nevertheless, in proliferating cells the percentage of nuclei with a number of signals different from the expected (two unreplicated chromosomes per pair) was different from that found in non-dividing cells (P < 0.05). It was estimated that 10.8% of double dots in dividing cells resulted from DNA replication. The sequence of replication was first the locus-specific region, second a telomere region, and third the centromere. In conclusion, the DNA replication process could result in errors of interpretation (misdiagnosis) in 7% of proliferating cells. Thus, the use of a cell cycle phase-specific marker could avoid errors by indicating the cell stage in which the nucleus analysed is found.     

The consequence of maximum thermodynamic efficiency in Daisyworld

The imaginary planet of Daisyworld is the simplest model used to illustrate the implications of the Gaia hypothesis. The dynamics of daisies and their radiative interaction with the environment are described by fundamental equations of population ecology theory and physics. The parameterization of the turbulent energy flux between areas of different biological cover is similar to the diffusive-type approximation used in simple climate models. Here I show that the small variation of the planetary diffusivity adopted in the classical version of Daisyworld limits the range of values for the solar insolation for which biota may grow in the planet.Recent studies suggest that heat transport in a turbulent medium is constrained to maximize its efficiency. This condition is almost equivalent to maximizing the rate of entropy production due to non-radiative sources. Here, I apply the maximum entropy principle (MEP) to Daisyworld. I conclude that the MEP sets the maximum range of values for the solar insolation with a non-zero amount of daisies. Outside this range, daisies cannot grow in the planet for any physically realistic climate distribution. Inside this range, I assume a distribution of daisies in agreement with the MEP. The results substantially enlarge the range of climate stability, due to the biota, in comparison to the classical version of Daisyworld. A very stable temperature is found when two different species grow in the planet.     

Molecular cloning and characterization of a multidomain endoglucanase from Paenibacillus sp BP-23: evaluation of its performance in pulp refining

The gene celB encoding an endoglucanase from Paenibacillus sp. BP-23 was cloned and expressed in Escherichia coli. The nucleotide sequence of a 4161 bp DNA fragment containing the celB gene was determined, revealing an open reading frame of 2991 nucleotides that encodes a protein of 106,927 Da. Comparison of the deduced amino acid sequence of endoglucanase B with known β-glycanase sequences showed that the encoded enzyme is a modular protein and exhibits high homology to enzymes belonging to family 9 cellulases. The celB gene product synthesized in E. coli showed high activity on carboxymethyl cellulose and lichenan while low activity was found on Avicel. Activity was enhanced in the presence of 10 mM Ca²⁺ and showed its maximum at 53 °C and pH 5.5. The effect of the cloned enzyme in modifying the physical properties of pulp and paper from Eucalyptus was tested (CelB treatment). An increase in mechanical strength of paper and a decrease in pulp dewatering properties were found, indicating that CelB treatment can be considered as a biorefining. Treatment with CelB gave rise to an improvement in paper strength similar to that obtained with 1,000 revolutions increase in mechanical refining. Comparison with the performances of recently developed endoglucanase A from the same strain and with a commercial cellulase showed that CelB produced the highest refining effect. Received: 25 February 2000 / Received revision: 4 July 2000 / Accepted: 9 July 2000     

Stoichiometry and compartmentation of NADH metabolism in Saccharomyces cerevisiae

In Saccharomyces cerevisiae, reduction of NAD(+) to NADH occurs in dissimilatory as well as in assimilatory reactions. This review discusses mechanisms for reoxidation of NADH in this yeast, with special emphasis on the metabolic compartmentation that occurs as a consequence of the impermeability of the mitochondrial inner membrane for NADH and NAD(+). At least five mechanisms of NADH reoxidation exist in S. cerevisiae. These are: (1) alcoholic fermentation; (2) glycerol production; (3) respiration of cytosolic NADH via external mitochondrial NADH dehydrogenases; (4) respiration of cytosolic NADH via the glycerol-3-phosphate shuttle; and (5) oxidation of intramitochondrial NADH via a mitochondrial 'internal' NADH dehydrogenase. Furthermore, in vivo evidence indicates that NADH redox equivalents can be shuttled across the mitochondrial inner membrane by an ethanol-acetaldehyde shuttle. Several other redox-shuttle mechanisms might occur in S. cerevisiae, including a malate-oxaloacetate shuttle, a malate-aspartate shuttle and a malate-pyruvate shuttle. Although key enzymes and transporters for these shuttles are present, there is as yet no consistent evidence for their in vivo activity. Activity of several other shuttles, including the malate-citrate and fatty acid shuttles, can be ruled out based on the absence of key enzymes or transporters. Quantitative physiological analysis of defined mutants has been important in identifying several parallel pathways for reoxidation of cytosolic and intramitochondrial NADH. The major challenge that lies ahead is to elucidate the physiological function of parallel pathways for NADH oxidation in wild-type cells, both under steady-state and transient-state conditions. This requires the development of techniques for accurate measurement of intracellular metabolite concentrations in separate metabolic compartments.