Biosynthesis of Ochratoxin A

Biosynthesis of ochratoxin A by Aspergillus ochraceus Wilh. was investigated by radiolabeling experiments in which phenylalanine-1-¹⁴C and sodium acetate-2-¹⁴C were supplied to the fungus in sucrose-yeast extract medium. Results showed that phenylalanine was incorporated unaltered into the phenylalanine moiety of ochratoxin A, whereas the isocoumarin moiety of ochratoxin A was mostly derived via acetate condensation.     

Long-wavelength sensitive visual pigments of the guppy (<Emphasis Type="Italic">Poecilia reticulata</Emphasis>): six opsins expressed in a single individual

Background

The diversity of visual systems in fish has long been of interest for evolutionary biologists and neurophysiologists, and has recently begun to attract the attention of molecular evolutionary geneticists. Several recent studies on the copy number and genomic organization of visual pigment proteins, the opsins, have revealed an increased opsin diversity in fish relative to most vertebrates, brought about through recent instances of opsin duplication and divergence. However, for the subfamily of opsin genes that mediate vision at the long-wavelength end of the spectrum, the LWS opsins, it appears that most fishes possess only one or two loci, a value comparable to most other vertebrates. Here, we characterize the LWS opsins from cDNA of an individual guppy, Poecilia reticulata, a fish that is known exhibit variation in its long-wavelength sensitive visual system, mate preferences and colour patterns.

Results

We identified six LWS opsins expressed within a single individual. Phylogenetic analysis revealed that these opsins descend from duplication events both pre-dating and following the divergence of the guppy lineage from that of the bluefin killifish, Lucania goodei, the closest species for which comparable data exists. Numerous amino acid substitutions exist among these different LWS opsins, many at sites known to be important for visual pigment function, including spectral sensitivity and G-protein activation. Likelihood analyses using codon-based models of evolution reveal significant changes in selective constraint along two of the guppy LWS opsin lineages.

Conclusion

The guppy displays an unusually high number of LWS opsins compared to other fish, and to vertebrates in general. Observing both substitutions at functionally important sites and the persistence of lineages across species boundaries suggests that these opsins might have functionally different roles, especially with regard to G-protein activation. The reasons why are currently unknown, but may relate to aspects of the guppy's behavioural ecology, in which both male colour patterns and the female mate preferences for these colour patterns experience strong, highly variable selection pressures.

     

Distinct modulation of voltage-gated and ligand-gated Ca2+ currents by PPAR-γ agonists in cultured hippocampal neurons

Type 2 diabetes mellitus is a metabolic disorder characterized by hyperglycemia and is especially prevalent in the elderly. Because aging is a risk factor for type 2 diabetes mellitus, and insulin resistance may contribute to the pathogenesis of Alzheimer's disease (AD), anti-diabetic agents (thiazolidinediones-TZDs) are being studied for the treatment of cognitive decline associated with AD. These agents normalize insulin sensitivity in the periphery and can improve cognition and verbal memory in AD patients. Based on evidence that Ca²⁺ dysregulation is a pathogenic factor of brain aging/AD, we tested the hypothesis that TZDs could impact Ca²⁺ signaling/homeostasis in neurons. We assessed the effects of pioglitazone and rosiglitazone (TZDs) on two major sources of Ca²⁺ influx in primary hippocampal cultured neurons, voltage-gated Ca²⁺ channel (VGCC) and the NMDA receptor (NMDAR). VGCC- and NMDAR-mediated Ca²⁺ currents were recorded using patch-clamp techniques, and Ca²⁺ intracellular levels were monitored with Ca²⁺ imaging techniques. Rosiglitazone, but not pioglitazone reduced VGCC currents. In contrast, NMDAR-mediated currents were significantly reduced by pioglitazone but not rosiglitazone. These results show that TZDs modulate Ca²⁺-dependent pathways in the brain and have different inhibitory profiles on two major Ca²⁺ sources, potentially conferring neuroprotection to an area of the brain that is particularly vulnerable to the effects of aging and/or AD.     

Hydrogen sulfide consumption measured at low steady state concentrations using a sulfidostat

Although >10 microM hydrogen sulfide typically is toxic to eukaryotic cells, <1 microM sulfide is rapidly consumed and oxidized. To measure sulfide consumption in such low concentrations, we built a "Sulfidostat." The apparatus uses a sulfide-specific electrode to measure the concentration of free sulfide. The electrode is connected to a computer that controls a syringe pump. The pump injects Na(2)S solution into the sample chamber to maintain a constant concentration. Since the response of the electrode to low sulfide concentrations at neutral pH had not been previously validated, that was measured. Then using the Sulfidostat, the rate of sulfide consumption is the rate at which it is pumped into the sample to maintain a constant concentration. The protozoan Tetrahymena pyriformis was used to demonstrate the apparatus; maximum sulfide consumption occurred near 0.5 microM sulfide at a rate of 250 nmol (g protein)(-1) s(-1). That is higher than the rate calculated from the disappearance of sulfide following a bolus addition, a difference that can be explained by the slow response of the electrode and by reversible binding of sulfide by the cells. The Sulfidostat can measure sulfide consumption at concentrations lower than previously have been possible.     

Metabolic integration during the evolutionary origin of mitochondria

Although mitochondria provide eukaryotic cells with certain metabolic advantages, in other ways they may be disadvantageous. For example, mitochondria produce reactive oxygen species that damage both nucleocytoplasm and mitochondria, resulting in mutations, diseases, and aging. The relationship of mito-chondria to the cytoplasm is best understood in the context of evolutionary history. Although it is clearthat mitochondria evolved from symbiotic bacteria, the exact nature of the initial symbiosis is a matter of continuing debate. The exchange of nutrients between host and symbiont may have differed from that be-tween the cytoplasm and mitochondria in modern cells. Speculations about the initial relationships includethe following. (1) The pre-mitochondrion may have been an invasive, parasitic bacterium. The host did notbenefit. (2) The relationship was a nutritional syntrophy based upon transfer of organic acids from host tosymbiont. (3) The relationship was a syntrophy based upon H2 transfer from symbiont to host, where thehost was a methanogen. (4) There was a syntrophy based upon reciprocal exchange of sulfur compounds.The last conjecture receives support from our detection in eukaryotic cells of substantial H2S-oxidizing activity in mitochondria, and sulfur-reducing activity in the cytoplasm.     

Quality of song learning affects female response to male bird song

Bird song is unusual as a sexually selected trait because its expression depends on learning as well as genetic and other environmental factors. Prior work has demonstrated that males who are deprived of the opportunity to learn produce songs that function little if at all in male-female interactions. We asked whether more subtle variation in male song-learning abilities influences female response to song. Using a copulation solicitation assay, we measured the response of female song sparrows (Melospiza melodia) to songs of laboratory-reared males that differed in the amount of learned versus invented material that they included and in the degree to which learned material accurately matched the model from which it was copied. Females responded significantly more to songs that had been learned better, by either measure. Females did not discriminate between the best-learned songs of laboratory-reared males and songs of wild males used as models during learning. These results provide, to our knowledge, a first experimental demonstration that variation in learning abilities among males plays a functionally important part in the expression of a sexually selected trait, and further provide support for the hypothesis that song functions as an indicator of male quality because it reflects variation in response to early developmental stress.     

DEVELOPMENTAL SELECTION IN RESPONSE TO ENVIRONMENTAL CONDITIONS OF THE MATERNAL PARENT IN MIMULUS GUTTATUS

Copper tolerance is expressed in the diploid sporophyte as well as the microgametophyte of Mimulus guttatus. Previous studies, based on reproductive output, suggested that selection for copper tolerance could occur within the pistil. The objective of this study was to determine if selection within the pistil can increase sporophytic tolerance to copper and to determine whether this selection occurs pre- or postzygotically. Mixtures of pollen from copper tolerant or sensitive sources or from plants heterozygous for tolerance to copper were applied at two intensities to plants cloned and grown in control or copper supplemented solutions. The proportion of copper tolerant progeny showed a small, 7%, but significant increase when pollen recipients were grown with added copper. Comparisons of the numbers of tolerant progeny, as well as various components of reproduction, following light and heavy pollinations suggested that microgametophytic selection was unlikely to account for this increase. However, the 8 to 10% decrease in the seed/zygote ratio, compared to control values, was sufficient to account for the difference in proportion of copper tolerant progeny from control and copper treated plants. Thus, it appeared likely that selection for copper tolerance could occur within the pistil, and that much of this selection occurred postzygotically through the early failure of developing seeds.