A model of globin evolution

Putative globins have been identified in 426 bacterial, 32 Archaeal and 67 eukaryote genomes. Among these sequences are the hitherto unsuspected presence of single domain sensor globins within Bacteria, Fungi, and a Euryarchaeote. Bayesian phylogenetic trees suggest that their occurrence in the latter two groups could be the result of lateral gene transfer from Bacteria. Iterated psiblast searches based on groups of globin sequences indicate that bacterial flavohemoglobins are closer to metazoan globins than to the other two lineages, the 2-over-2 globins and the globin-coupled sensors. Since Bacteria is the only kingdom to have all the subgroups of the three globin lineages, we propose a working model of globin evolution based on the assumption that all three lineages originated and evolved only in Bacteria. Although the 2-over-2 globins and the globin-coupled sensors recognize flavohemoglobins, there is little recognition between them. Thus, in the first stage of globin evolution, we favor a flavohemoglobin-like single domain protein as the ancestral globin. The next stage comprised the splitting off to single domain 2-over-2 and sensor-like globins, followed by the covalent addition of C-terminal domains resulting in the chimeric flavohemoglobins and globin-coupled sensors. The last stage encompassed the lateral gene transfers of some members of the three globin lineages to specific groups of Archaea and Eukaryotes.     

Mammalian retinal horizontal cells are unconventional GABAergic neurons

Lateral interactions at the first retinal synapse have been initially proposed to involve GABA by transporter-mediated release from horizontal cells, onto GABA(A) receptors expressed on cone photoreceptor terminals and/or bipolar cell dendrites. However, in the mammalian retina, horizontal cells do not seem to contain GABA systematically or to express membrane GABA transporters. We here report that mouse retinal horizontal cells express GAD65 and/or GAD67 mRNA, and were weakly but consistently immunostained for GAD65/67. While GABA was readily detected after intracardiac perfusion, it was lost during classical preparation for histology or electrophysiology. It could not be restored by incubation in a GABA-containing medium, confirming the absence of membrane GABA transporters in these cells. However, GABA was synthesized de novo from glutamate or glutamine, upon addition of pyridoxal 5'-phosphate, a cofactor of GAD65/67. Mouse horizontal cells are thus atypical GABAergic neurons, with no functional GABA uptake, but a glutamate and/or glutamine transport system allowing GABA synthesis, probably depending physiologically from glutamate released by photoreceptors. Our results suggest that the role of GABA in lateral inhibition may have been underestimated, at least in mammals, and that tissue pre-incubation with glutamine and pyridoxal 5'-phosphate should yield a more precise estimate of outer retinal processing.     

The intron 7 donor splice site transition: a second Tay-Sachs disease mutation in French Canada

Mutations at the hexosaminidase A (HEXA) gene which cause Tay-Sachs disease (TSD) have elevated frequency in the Ashkenazi Jewish and French-Canadian populations. We report a novel TSD allele in the French-Canadian population associated with the infantile form of the disease. The mutation, a GA transition at the +1 position of intron 7, abolishes the donor splice site. Cultured human fibroblasts from a compound heterozygote for this transition (and for a deletion mutation) produce no detectable HEXA mRNA. The intron 7+1 mutation occurs in the base adjacent to the site of the adult-onset TSD mutation (G805A). In both mutations a restriction site for the endonuclease EcoRII is abolished. Unambiguous diagnosis, therefore, requires allele-specific oligonucleotide hybridization to distinguish between these two mutant alleles. The intron 7+1 mutation has been detected in three unrelated families. Obligate heterozygotes for the intron 7+1 mutation were born in the Saguenay-Lac-St-Jean region of Quebec. The most recent ancestors common to obligate carriers of this mutation were from the Charlevoix region of the province of Quebec. This mutation thus has a different geographic centre of diffusion and is probably less common than the exon 1 deletion TSD mutation in French Canadians. Neither mutation has been detected in France, the ancestral homeland of French Canada.     

Chain-chain interactions for methyl polygalacturonate: models for high methyl-esterified pectin junction zones

The ability of pectins to form gels in the presence of calcium is well-known, and it implies the interaction of carboxylate groups and bivalent ions. However, even when most of the galacturonic units are methyl esterified, pectins are able to form gels but only under certain experimental conditions. In this case, hydrogen bonding and hydrophobic interactions are believed to be responsible for gel formation, and it is likely, as in the other mechanisms of polysaccharide gel formation, that stable junction zones consist of cooperatively ordered chains linked together throughout nonbonded interactions to provide a three-dimensional network. To investigate the junction zones in HM-pectin gels, we investigated, by molecular modeling, all of the ways to associate two, and then three, fully methyl-esterified galacturonic acid chains. Two models are obtained: the first one is based on a packing of parallel chains; it agrees with the hypothetical model derived from fiber diffraction study; the second one displays an antiparallel orientation of the chains; it presents a better arrangement of the chains and, theoretically, a much lower potential energy. In both cases, all of the favorable associations occur within a network of hydrogen bonds and of hydrophobic contacts.     

Haem ligands of the ferricytochrome c of Ustilago sphaerogena

The mammalian-type cytochrome c of the basidiomycete Ustilago sphaerogena contains in a single polypeptide chain of 107 residues, two histidine residues located at positions 18 and 33, and one methionine residue situated at position 80 (Bitar et al., 1972). The reaction of Ustilago ferricytochrome c with bromoacetate at neutral pH resulted in the modification of histidine-33, but not of histidine-18 or of the invariant methionine residue. The activities of Ustilago cytochrome c with mitochondrial cytochrome c oxidase and with NADH-cytochrome c reductase were unaltered by the modification. The equilibrium constants for the formation of low-spin complexes of the ferrihaem octapeptide of horse cytochrome c (residues 14-21, including the haem bound covalently to cysteines 14 and 17) with imidazole, N(2)-acetylhistidine and monocarboxymethyl derivatives of N(2)-acetylhistidine were determined spectrophotometrically. Alkylation of the imidazole side-chain group of N(2)-acetylhistidine resulted in a marked decrease in its ability to form low-spin ferrihaem complexes. These results indicate that in Ustilago ferricytochrome c in solution histidine-33 is not involved in the central co-ordination complex. Since side-chain groups of residues other than histidine and methionine do not appear to be involved in the central complexes of other mammalian-type cytochromes c (Hettinger & Harbury, 1964, 1965; Myer & Harbury, 1965) it is likely that in Ustilago ferricytochrome c in solution at neutral pH, the side-chain groups of histidine-18 and methionine-80 are involved in the central co-ordination complex. The latter is stable over the pH range 2.6-8.4.     

Queen-worker conflict over sex ratio: A comparison of primary and secondary sex ratios in the Argentine ant,Iridomyrmex humilis

We compare the primary sex ratio (proportion of haploid eggs laid by queens) and the secondary sex ratio (proportion of male pupae produced) in the Argentine ant Iridomyrmex humilis with the aim of investigating whether workers control the secondary sex ratio by selectively eliminating male brood. The proportion of haploid eggs produced by queens was close to 0.5 in late winter, decreased to less than 0.3 in spring and summer, and increased again to a value close to 0.5 in fall. Laboratory experiments indicate that temperture is a proximate factor influencing the primary sex ratio with a higher proportion of haploid eggs being laid at colder temperatures. Production of queen pupae ceased in mid-June, about three weeks before that of male pupae. After this time only worker pupae were produced. During the period of production of sexuals, the proportion of male pupae ranged from 0.30 to 0.38. Outside this period no males were reared although haploid eggs were produced all the year round by queens. Workers thus exert a control on the secondary sex ratio by eliminating a proportion of the male brood during the period of sexual production and eliminating all the males during the remainder of the cycle. These data are consistent with workers preferring a more female-biased sex ratio than queens. The evolutionary significance of the production of male eggs by queens all the year round is as yet unclear. It may be a mechanism allowing queen replacement in the case of the death of the queens in the colony.     

Induction of alternative oxidase synthesis by herbicides inhibiting branched-chain amino acid synthesis

Sycamore suspension cells ( Acer pseudoplatanus L.) were incubated in the presence of sulfonylurea and imidazolinone herbicides. These inhibitors of acetolactate synthase (ALS), a key enzyme of branched-chain amino acid synthesis, triggered a dramatic induction of the alternative oxidase (AOX). AOX activity increased in treated cells, eventually exceeding cytochrome (cyt) pathway activity. This induction of AOX activity was correlated with the accumulation of a 35 kDa AOX protein in isolated mitochondria, detected by Western blotting with a monoclonal antibody against Sauromatum guttatum AOX. It was preceded by the accumulation of putative 1.6 kb AOX mRNA, detected using an Aox cDNA probe from soybean. The metabolic perturbations induced by the herbicides rather than the herbicide molecules themselves were responsible for this induction of AOX. However, α-oxobutyrate (one of the substrates of ALS) and its transamination product, α-aminobutyrate, which accumulated after herbicide treatment, were not involved. The inhibition of branched-chain amino acid synthesis was probably somehow responsible for the AOX induction since: (i) a mixture of those amino acids (leucine, isoleucine, valine) prevented AOX induction by ALS inhibitors; (ii) the herbicide Hoe 704, a potent inhibitor of acetolactate reducto-isomerase (the enzyme following ALS in the branched-chain amino acid pathway), also triggered AOX induction.     

Integrating Pathways of Parkinson's Disease in a Molecular Interaction Map

Parkinson's disease (PD) is a major neurodegenerative chronic disease, most likely caused by a complex interplay of genetic and environmental factors. Information on various aspects of PD pathogenesis is rapidly increasing and needs to be efficiently organized, so that the resulting data is available for exploration and analysis. Here we introduce a computationally tractable, comprehensive molecular interaction map of PD. This map integrates pathways implicated in PD pathogenesis such as synaptic and mitochondrial dysfunction, impaired protein degradation, alpha-synuclein pathobiology and neuroinflammation. We also present bioinformatics tools for the analysis, enrichment and annotation of the map, allowing the research community to open new avenues in PD research. The PD map is accessible at http://minerva.uni.lu/pd_map.     

Threats to and conservation of North African wetlands: the case of the Ramsar site of Beni-Belaid (NE Algeria)

Because of their biogeographical and geomorphological context, the northeastern Algeria wetlands present high species and community richness. The vegetation study of the Ramsar site of Beni-Belaid (Kabylia) showed the existence of four main communities, distributed along gradients of hydrology and disturbance. The obtained results reveal worrying threats on short term: overgrazing results in the lake invasion by the sand eroded from the coastal dune; agriculture induces illegal cutting, water pollution and excessive groundwater pumping; finally, hunting and fishing are illegally practiced into the Ramsar site. The awareness of public authorities is needed in order: (1) to completely protect the wetland with the aim of restoring a riparian forest belt; and (2) to initiate a campaign for increasing the local population awareness, and its involvement in conservation programs.