Post-glacial colonization of Western Europe brown bears from a cryptic Atlantic refugium out of the Iberian Peninsula

The European brown bear (Ursus arctos) shows a particular phylogeography that has been used to illustrate the model for contraction-expansion dynamics related to glacial refugia in Southern European peninsulas. Recent studies, however, have nuanced the once generally accepted paradigm, indicating the existence of cryptic refugia for some species further north. In this paper we collected available data on chronology and mitochondrial haplotypes from Western European brown bears, adding new sequences from present day individuals from the Cantabrian (North Iberia) area, in order to reconstruct the dynamics of the species in the region. Both genetics and chronology show that the Iberian Pleistocene lineages were not the direct ancestors of the Holocene ones, the latter entering the Peninsula belatedly (around 10,000 years BP) with respect to other areas such as the British Isles. We therefore propose the existence of a cryptic refugium in continental Atlantic Europe, from where the bears would expand as the ice receded. The delay in the recolonization of the Iberian Peninsula could be due to the orographic characteristics of the Pyrenean-Cantabrian region and to the abundant presence of humans in the natural entrance to the Peninsula.     

Decreased Density of Presynaptic α2-Adrenoceptors in Postmortem Brains of Patients with Alzheimer''s Disease

The full agonist [3H]bromoxidine (UK 14304) was used to quantitate alpha 2-adrenoceptors in postmortem brains of patients with Alzheimer's disease. The effects of aging and human serum Cohn fraction IV on [3H]bromoxidine binding were also assessed. In patients with Alzheimer's disease, the binding capacity (Bmax) of [3H]bromoxidine was lower in the frontal cortex (37%), hypothalamus (33%), and cerebellum (52%) than in matched controls. In the hippocampus, amygdala, and head of caudate, the binding capacities (Bmax) were unchanged. Quantitative autoradiographic analyses with [3H]bromoxidine confirmed the existence of a marked reduction (55-60%) in alpha 2A-adrenoceptor density in the frontal cortex (layers I and III). In patients with dementia who did not meet neuropathological criteria for Alzheimer's disease, the density of alpha 2-adrenoceptors was unchanged. In control subjects, the density of alpha 2A-adrenoceptors in the frontal cortex showed a significant negative correlation with age at death. The inhibitory effect of human serum Cohn fraction IV on [3H]bromoxidine was very similar in control subjects and patients with Alzheimer's disease. The observed decrease in the density of brain alpha 2-adrenoceptors in Alzheimer's disease may represent direct biochemical evidence of a presynaptic location of this receptor on noradrenergic nerve terminals in the human CNS.     

Effect of caffeine on G2 repair and its reversion by adenosine

Chromosome damage induced in root meristems of Allium cepa L. by an 18-h treatment with 5-aminouracil (AU) was enhanced by 2-h pulses with 5 mM caffeine, the most effective pulse being given from the 8th to the 10th h after AU. Chromosome damage was detected by the percentage of anaphases or telophases showing chromosomal aberrations. This caffeine effect was partially reversed by adenosine. We suggest that this caffeine anti-repair effect could be due to a competition between methylxanthine and an adenine-nucleotide derivative (ATP?) required for some step(s) of G₂-prophase repair.     

Superstoichiometric binding of L-Phe to phenylalanine hydroxylase from Caenorhabditis elegans: evolutionary implications

Phenylalanine hydroxylase (PAH) catalyzes the hydroxylation of L-Phe to L-Tyr. Dysfunctional PAH results in phenylketonuria and mammalian PAH is therefore highly regulated and displays positive cooperativity for L-Phe (Hill coefficient (h) = 2). L-Phe does not bind to the regulatory ACT domain in full-length tetrameric human PAH and cooperativity is elicited by homotropic binding to the catalytic site (Thórólfsson et al. in Biochemistry 41:7573–7585, 2002). PAH from Caenorhabditis elegans (cePAH) is devoid of cooperativity for L-Phe (h = 0.9), and, as shown in this work, structural analysis reveal an additional L-Phe binding site at the regulatory domain of full-length cePAH. This site involves the GA(S)L/ISRP motifs, which are also found in ACT domains of other L-Phe binding proteins, such as prephenate dehydratase. Isothermal titration calorimetry further demonstrated 2 binding sites per subunit for cePAH versus ~1 for hPAH. Steric occlusion of the regulatory site, notably by residues Lys215/Tyr216 from the adjacent catalytic domain, appears to hinder regulatory binding in full-length hPAH. Accordingly, the humanized mutant Q215K/N216Y of cePAH binds ~1.4 L-Phe/subunit. This mutant also displays high catalytic activity and certain positive cooperativity for L-Phe (h = 1.4). Our results support that the acquisition of positive cooperativity in mammalian forms of PAH is accompanied by a closure of the regulatory L-Phe binding site. Concomitantly, the function of the regulatory ACT domain appears to be adapted from amino acid binding to serving the communication of conformational changes among catalytic subunits.     

EATB Donor Case Workshop 2007

The European Association of Tissue Banks (EATB) Donor Case Workshop is a forum held within the programme of the EATB annual Congress since 2003. This workshop has been used to discuss clinical donor cases with peer review of practice. It was agreed in advance that the experience of the 2007 workshop should be shared by publication as an example of participative learning which can be extended to other fields within tissue banking and which may be applicable in other disciplines. The EATB Congress in 2008 will extend the idea of participative open workshops with two additional workshops, one on Quality System cases and another on heart valve cases.     

Survival strategies of plasmid-carrier and plasmidless Escherichia coli strains under illuminated and non-illuminated conditions, in a fresh water ecosystem

A Comparative study, in illuminated and non-illuminated systems, was made to determine the survival strategies of plasmid-carrier and plasmidless bacteria in sterile river water. Two strains of Escherichia coli from river water were selected: one plasmidless, EC1, and one antibiotic-resistant strain, EC7, which showed plasmid bands. By matings with EC7 as donor and E. coli K12 strain J62 as recipient, transconjugants were generated, the J62₇ strain, which showed both antibiotic resistance and plasmid bands. Ethidium bromide curing of the EC7 strain generated the EC7₂ strain which showed a partial loss of resistance and a reorganization of plasmid bands. Under non-illuminated conditions the total number of cells detected by direct count and the number of culturable cells (injured and non-injured cells) remained practically constant throughout the period of incubation. In the illuminated systems, however, the number of cfu decreased in four of the five strains studied. The greatest decreases are those of the J62 strain, followed by those of the J62₇, EC1, EC7₂ and EC7 strains. Differences in survival strategies as a consequence of the presence or absence of plasmids are discussed.