Evolution of duplicate genes in a tetraploid animal, Xenopus laevis

To understand the evolution of duplicate genes, we compared rates of nucleotide substitution between 17 pairs of nonallelic duplicated genes in the tetraploid frog Xenopus laevis with rates between the orthologous loci of human and rodent. For all duplicated X. laevis genes, the number of synonymous substitutions per site (dS) was greater than the number of nonsynonymous substitutions per site (dN), indicating that these genes are subject to purifying selection. There was also a significant positive correlation (r = 0.915) between dN for the X. laevis genes and dN for the mammalian genes, suggesting that, at the amino acid level, the X. laevis genes and the mammalian genes are under similar constraints. Results of relative-rate tests showed nearly equal rates of nonsynonymous substitution in each copy of the X. laevis genes; apparently there are similar constraints on both copies. No correlation was found between dS for the X. laevis genes and dS for the mammalian genes. There was a significant positive correlation both between members of pairs of duplicated X. laevis genes (r = 0.951) and between human and rodent orthologues (r = 0.854) with respect to third- position G+C content but no such relationship between the X. laevis genes and either of their mammalian orthologues. The results indicate that both copies of a duplicate gene can be subject to purifying selection and thus support the hypothesis of selection against all genotypes containing a null allele at either of two duplicate loci.      

Conformation and quantification of chloramphenicol in cow's urine, muscle and eggs by electron capture negative ion chemical ionization gas chromatography/mass spectrometry.

A method is described for the determination of residues of the antibiotic chloramphenicol in biological samples. The method is based on gas chromatography/negative ion chemical ionization mass spectrometry and uses (37Cl2)chloramphenicol as internal standard. Selective ion monitoring of four analyte-specific ions enables the determination of chloramphenicol levels in urine of 3 micrograms l-1 with a coefficient of variation of 8%. The limit of detection of the method is 0.1 p.p.b. for urine, muscle and egg.     

Microbial growth on peptones from fish industrial wastes

Industrial fish peptone was an excellent substrate for biomass production in solid and submerged fermentations. The maximal growth rates of several microorganisms were two to three times higher than those grown on beef (bacto)peptones and the final biomass concentrations were almost twice as great as those grown on beef peptones. Fish peptones did not increase the production of secondary metabolites relative to those produced on beef peptones in non-optimized media. Fish peptone has promising potential as a substrate for biomass production.     

Pristanic acid and phytanic acid: naturally occurring ligands for the nuclear receptor peroxisome proliferator-activated receptor alpha

Phytanic acid and pristanic acid are branched-chain fatty acids, present at micromolar concentrations in the plasma of healthy individuals. Here we show that both phytanic acid and pristanic acid activate the peroxisome proliferator-activated receptor alpha (PPARalpha) in a concentration-dependent manner. Activation is observed via the ligand-binding domain of PPARalpha as well as via a PPAR response element (PPRE). Via the PPRE significant induction is found with both phytanic acid and pristanic acid at concentrations of 3 and 1 microM, respectively. The trans-activation of PPARdelta and PPARgamma by these two ligands is negligible. Besides PPARalpha, phytanic acid also trans-activates all three retinoic X receptor subtypes in a concentration-dependent manner. In primary human fibroblasts, deficient in phytanic acid alpha-oxidation, trans-activation through PPARalpha by phytanic acid is observed. This clearly demonstrates that phytanic acid itself, and not only its metabolite, pristanic acid, is a true physiological ligand for PPARalpha. Because induction of PPARalpha occurs at ligand concentrations comparable to the levels found for phytanic acid and pristanic acid in human plasma, these fatty acids should be seen as naturally occurring ligands for PPARalpha.These results demonstrate that both pristanic acid and phytanic acid are naturally occurring ligands for PPARalpha, which are present at physiological concentrations.     

Hip joint replacement surgery for idiopathic osteoarthritis aggregates in families

In order to determine whether there is a genetic component to hip or knee joint failure due to idiopathic osteoarthritis (OA), we invited patients (probands) undergoing hip or knee arthroplasty for management of idiopathic OA to provide detailed family histories regarding the prevalence of idiopathic OA requiring joint replacement in their siblings. We also invited their spouses to provide detailed family histories about their siblings to serve as a control group. In the probands, we confirmed the diagnosis of idiopathic OA using American College of Rheumatology criteria. The cohorts included the siblings of 635 probands undergoing total hip replacement, the siblings of 486 probands undergoing total knee replacement, and the siblings of 787 spouses. We compared the prevalence of arthroplasty for idiopathic OA among the siblings of the probands with that among the siblings of the spouses, and we used logistic regression to identify independent risk factors for hip and knee arthroplasty in the siblings. Familial aggregation for hip arthroplasty, but not for knee arthroplasty, was observed after controlling for age and sex, suggesting a genetic contribution to end-stage hip OA but not to end-stage knee OA. We conclude that attempts to identify genes that predispose to idiopathic OA resulting in joint failure are more likely to be successful in patients with hip OA than in those with knee OA.     

Rapid evolution of immunoglobulin superfamily C2 domains expressed in immune system cells

To test the hypothesis that proteins expressed in cells of the vertebrate immune system evolve unusually rapidly, 107 orthologous immunoglobulin C2 domains were compared between human and murine rodent. The analysis showed that the rate of nonsynonymous (amino-acid- altering) nucleotide substitution in these domains was correlated with factors associated with protein structure and with breadth of tissue expression, as well as with the rate of synonymous substitution. However, when such factors were controlled for statistically, there remained a strong positive association between expression in the immune system and nonsynonymous rate, with the highest rates being seen in genes expressed in the immune system only. Certain immune system genes are known to be subject to positive selection favoring diversity at the amino acid level; most of these genes encode receptors that interact directly with foreign antigens. The observed acceleration of the rate of nonsynonymous evolution in C2 domains of immune system proteins may be explained by either (1) reduced constraint at the amino acid level on molecules interacting with immune system receptors that are themselves evolving rapidly due to positive diversifying selection or (2) positive selection favoring amino acid changes correlated with changes in the immune system receptors.