[The out-of-home care of HIV-infected children]. / L'accueil de l'enfant infecté par le VIH dans le milieu scolaire et résidentiel.

OBJECTIVE: To improve the conditions of out-of-home care of HIV-infected children. METHODS: Group discussions including staff members of 28 institutions having cared for an HIV-infected child with the objective to share 4 points of view: those of the HIV-infected child, of his parents, of the medical staff and of the out-of-home care professionals. RESULTS: Care professionals are uncomfortable with the confidentiality surrounding the diagnosis. The feeling of better controlling the risks justifies their wish to obtain medical information, although these risks are ill-defined. The contributions of the parents of HIV-infected children shed a light on the link between the disclosure of the child's diagnosis and their intimacy and family history. Role-playing games with constructed scenarios revealed fixed and absurd aspects of certain beliefs and the difficulties to put in practice the acquired knowledge. The legitimacy of desire of parenthood in HIV-infected adults was questioned by some of the care professionals and their social representation of the person living with HIV appeared ambiguous, reminding the stigma these families are still victims of. CONCLUSION: Improving the conditions of out-of-home care of HIV-infected children requires ethical, legal and scientific counseling and discussions in the setting that should occur independently of the presence of a child with HIV. The disclosure of the diagnosis should only occur, if necessary, for their well-being, with their or their parents' agreement.

Effect of dexamethasone on moesin gene expression in rabbit bone marrow stromal cells.

The influence of dexamethasone on rabbit bone marrow stromal cells differentiation was studied by screening the action of dexamethasone on gene expression. Using differential display, we observed some differential amplifications. The use of five of thirteen different primers combination allowed to identify one or more differential bands. One of them was identified as moesin gene. Real-time PCR confirmed a significant reduction of moesin gene expression following dexamethasone treatment. The decrease of expression for this protein, involved in cytoskeletal organization, could explain the effects of dexamethasone treatment on bone marrow stromal cells differentiation.

Biomarkers for the effects of benzodiazepines in healthy volunteers.

Studies of novel centrally acting drugs in healthy volunteers are traditionally concerned with kinetics and tolerability, but useful information may also be obtained from biomarkers of clinical endpoints. A useful biomarker should meet the following requirements: a consistent response across studies and drugs; a clear response of the biomarker to a therapeutic dose; a dose-response relationship; a plausible relationship between biomarker, pharmacology and pathogenesis. In the current review, all individual tests found in studies of benzodiazepine agonists registered for anxiety in healthy volunteers since 1966 were progressively evaluated for compliance with these requirements. A MedLine search yielded 56 different studies, investigating the effects of 16 different benzodiazepines on 73 different (variants of ) neuropsychological tests, which could be clustered into seven neuropsychological domains. Subjective and objective measures of alertness were most sensitive to benzodiazepines. The most consistent effects were observed on saccadic peak velocity (SPV) and visual analogue scores ( VAS) of alertness, where 100% and 79% of all studies respectively showed statistically significant effects. A dose-response relationship could be constructed for temazepam and SPV, which was used to determine dose equivalencies relative to temazepam, for seven different benzodiazepines. These dose equivalencies correlated with the lowest recommended daily maintenance dose (r2 = 0.737, P < 0.05). This relationship between SPV reduction and clinical efficacy could reflect the clinical practice of aiming for maximum tolerated levels, or it could represent a common basis behind SPV reduction and anxiolytic activity for benzodiazepines (probably sedation). The number of tests used in human psychopharmacology appears to be excessive and their sensitivity and reproducibility low.

TeV strings and the neutrino-nucleon cross section at ultrahigh energies.

In scenarios with the fundamental unification scale at the TeV one expects string excitations of the standard model fields at accessible energies. We study the neutrino-nucleon cross section in these models. We show that duality of the scattering amplitude forces the existence of a tower of massive leptoquarks that mediate the process in the s channel. Using the narrow-width approximation we find a sum rule for the production rate of resonances with different spin at each mass level. We show that these contributions can increase substantially the standard model neutrino-nucleon cross section, although they seem insufficient to explain the cosmic ray events above the Greisen-Zatsepin-Kuz'min cutoff energy.

Interplay between recombination, cell division and chromosome structure during chromosome dimer resolution in Escherichia coli.

Chromosome dimers form in bacteria by recombination between circular chromosomes. Resolution of dimers is a highly integrated process involving recombination between dif sites catalysed by the XerCD recombinase, cell division and the integrity of the division septum-associated FtsK protein and the presence of dif inside a restricted region of the chromosome terminus, the dif activity zone (DAZ). We analyse here how these phenomena collaborate. We show that (i) both inter- and intrachromosomal recombination between dif sites are activated by their presence inside the DAZ; (ii) the DAZ-specific activation only occurs in conditions supporting the formation of chromosome dimers; (iii) overexpression of FtsK leads to a general increase in dif recombination irrespective of dif location; (iv) overexpression of FtsK does not improve the ability of dif sites inserted outside the DAZ to resolve chromosome dimers. Our results suggest that the formation of an active XerCD-FtsK-dif complex is restricted to when a dimer is present, the features of chromosome organization that determine the DAZ playing a central role in this control.

Polarization of the Escherichia coli chromosome. A view from the terminus.

The E. coli chromosome replication arms are polarized by motifs such as RRNAGGGS oligomers, found preferentially on leading strands. Their skew increases regularly from the origin to dif (the site in the center of the terminus where chromosome dimer resolution occurs), to reach a value of 90% near dif. Convergent information indicates that polarization in opposite directions from the dif region controls tightly the activity of dif, probably by orienting mobilization of the terminus at cell division. Another example of polarization is the presence, in the region peripheral to the terminus, of small non-divisible zones whose inversion interferes with spatial separation of sister nucleoids. The two phenomena may contribute to the organization of the Ter macrodomain.

FtsK functions in the processing of a Holliday junction intermediate during bacterial chromosome segregation.

In bacteria with circular chromosomes, homologous recombination can generate chromosome dimers that cannot be segregated to daughter cells at cell division. Xer site-specific recombination at dif, a 28-bp site located in the replication terminus region of the chromosome, converts dimers to monomers through the sequential action of the XerC and XerD recombinases. Chromosome dimer resolution requires that dif is positioned correctly in the chromosome, and the activity of FtsK, a septum-located protein that coordinates cell division with chromosome segregation. Here, we show that cycles of XerC-mediated strand exchanges form and resolve Holliday junction intermediates back to substrate irrespective of whether conditions support a complete recombination reaction. The C-terminal domain of FtsK is sufficient to activate the exchange of the second pair of strands by XerD, allowing both intra- and intermolecular recombination reactions to go to completion. Proper positioning of dif in the chromosome and of FtsK at the septum is required to sense the multimeric state of newly replicated chromosomes and restrict complete Xer reactions to dimeric chromosomes.

Functional polarization of the Escherichia coli chromosome terminus: the dif site acts in chromosome dimer resolution only when located between long stretches of opposite polarity.

In Escherichia coli, chromosome dimers are generated by recombination between circular sister chromosomes. Dimers are lethal unless resolved by a system that involves the XerC, XerD and FtsK proteins acting at a site (dif) in the terminus region. Resolution fails if dif is moved from its normal position. To analyse this positional requirement, dif was transplaced to a variety of positions, and deletions and inversions of portions of the dif region were constructed. Resolution occurs only when dif is located at the convergence of multiple, oppositely polarized DNA sequence elements, inferred to lie in the terminus region. These polar elements may position dif at the cell septum and be general features of chromosome organization with a role in nucleoid dynamics.

Xer recombination in Escherichia coli. Site-specific DNA topoisomerase activity of the XerC and XerD recombinases.

Xer site-specific recombination functions in maintaining circular replicons in the monomeric state in Escherichia coli. Two recombinases of the bacteriophage lambda integrase family, XerC and XerD, are required for recombination at the chromosomal site, dif, and at a range of plasmid-borne sites. Xer recombination core sites contain the 11-base pair binding sites for each recombinase separated by a 6 to 8-base pair central region. We report that both XerC and XerD act as site-specific type I topoisomerases by relaxing supercoiled plasmids containing a dif site. Relaxation by either XerC or XerD occurs in the absence of the partner recombinase and requires only a single recombination core site. XerC or XerD relaxation activities are completely inhibited by the addition of the partner recombinase, providing that the DNA recognition sequence for the inhibiting partner is present.

Unraveling a region-specific hyper-recombination phenomenon: genetic control and modalities of terminal recombination in Escherichia coli.

The propensity of the terminus of the Escherichia coli chromosome for recombination has been further explored, using a test based on the selectable loss of a lambda prophage inserted between repeated sequences from Tn10. Terminal recombination appears region-specific and unrelated to replication termination in a strain harboring a major chromosomal rearrangement. It requires RecBC(D) activity and must therefore occur between sister chromosomes, to conserve genomic integrity in spite of DNA degradation by RecBCD. Terminal recombination is maximal in the dif region and its intensity on either side of this recombination site depends on the orientation of the repeated sequences, probably because of the single chi site present in each repeat. Additional observations support the model that the crossover is initiated by single-strand invasion between sister chromosomes followed by RecBCD action as a consequence of DNA breakage due to the initial invasion event. Crossover location within repeats inserted at dif position supports the possibility that sister chromosomes are tightly paired in the centre of the terminal recombination zone. These data reinforce the model that postreplicative reconstruction of nucleoid organization creates a localized synapsis between the termini of sister chromosomes.

Restriction of the activity of the recombination site dif to a small zone of the Escherichia coli chromosome.

The recombination site dif is the target on the Escherichia coli chromosome of the site-specific recombinases XerC and XerD. The dif/XerC-D system plays a role during the cell cycle, probably by favoring sister chromosome monomerization or separation. A phenomenon of regional control over dif activity, also analyzed in this issue, is demonstrated here by translocation of dif to a series of loci close to the normal locus. We found that the site is physiologically active only within a narrow zone around its natural position. Competence for dif activity does not depend on the sequence of the normal dif activity zone (DAZ), because delta(dif) deletions larger than the DAZ result in Dif+ bacteria when dif is reinserted at the junction point. Although dif maps where replication normally terminates, termination of replication is not the elicitor. A strain with a large inversion that places dif and its surrounding region close to oriC remains Dif+, even when a Tus- mutation allows replication to terminate far away from it. Preliminary data suggest the possibility that specialized sequences separate the competent zone from the rest of the chromosome. We suspect that these sequences are members of a set of sequences involved in a polarized process of postreplicative reconstruction of the nucleoid structure. We propose that this reconstruction forces catenation links between sister chromosomes to accumulate within the DAZ, where they eventually favor recombination at dif.

Hyperrecombination in the terminus region of the Escherichia coli chromosome: possible relation to nucleoid organization.

The terminus region of the Escherichia coli chromosome is the scene of frequent homologous recombination. This can be demonstrated by formation of deletions between directly repeated sequences which flank a genetic marker whose loss can be easily detected. We report here that terminal recombination events are restricted to a relatively large terminal recombination zone (TRZ). On one side of the TRZ, the transition from the region with a high excision rate to the normal (low) excision rates of the rest of the chromosome occurs along a DNA stretch of less than 1 min. No specific border of this domain has been defined. To identify factors inducing terminal recombination, we examined its relation to two other phenomena affecting the same region, site-specific recombination at the dif locus and site-specific replication pausing. Both the location and the efficiency of terminal recombination remained unchanged after inactivation of the dif-specific recombination system. Similarly, inactivation of site-specific replication pausing or displacement of the replication fork trap so that termination occurs about 200 kb away from the normal region had no clear effect on this phenomenon. Therefore, terminal recombination is not a direct consequence of either dif-specific recombination or replication termination. Furthermore, deletions encompassing the wild-type TRZ do not eliminate hyperrecombination. Terminal recombination therefore cannot be attributed to the activity of some unique sequence of the region. A possible explanation of terminal hyperrecombination involves nucleoid organization and its remodeling after replication: we propose that post replicative reconstruction of the nucleoid organization results in a displacement of the catenation links between sister chromosomes to the last chromosomal domain to be rebuilt. Unrelated to replication termination, this process would facilitate interactions between the catenated molecules and would make the domain highly susceptible to recombination between sister chromosomes.

Plasmid pSC101 harbors a recombination site, psi, which is able to resolve plasmid multimers and to substitute for the analogous chromosomal Escherichia coli site dif.

Plasmid pSC101 harbors a 28-bp sequence which is homologous to dif, the target site of the XerC/XerD-dependent recombination system in Escherichia coli. Using a technique which allows very sensitive detection of plasmid loss, we show that recombination at this site, termed psi for pSC101 stabilized inheritance, causes a moderate increase in pSC101 stability. The role of the psi sequence in site-specific recombination has been explored in two other contexts. It was cloned in a derivative of plasmid p15A and inserted into the chromosome in place of dif. In the first situation, psi activity requires accessory sequences and results in multimer resolution; in the second situation, it suppresses the effects of the dif deletion and can promote intermolecular exchanges. Thus, psi is a site whose recombinational activity depends on the context, the first in the cer/dif family known to exhibit such flexibility.

An estimate of the endogenous secretion rate of calcitonin in man.

1. The metabolic clearance rate (MCR) of human calcitonin was measured in 12 normal subjects and four patients with Paget's disease by the infusion of synthetic human calcitonin (15-40 microgram/h for 2-24 h), and in 10 additional patients with Paget's disease from the disappearance rate of immunoreactive calcitonin from plasma after the intravenous injection of large doses of synthetic human calcitonin (0.5-1.0 mg). 2. The estimated MCR during the infusion studies (range 531-1224 litres/day) was similar to that calculated from the disappearance of large doses of synthetic human calcitonin injected intravenously in patients with Paget's disease (mean = 1035 litres/day; range = 593-1408 litres/day). 3. An eightfold range in the basal values of plasma immunoreactive calcitonin, in spite of the presence of a relatively constant MCR, suggests that the variation in basal plasma calcitonin was due principally to variation in the endogenous secretion rate for calcitonin. 4. The results suggest that the endogenous secretion rate for calcitonin is low in normal subjects (mean 124 +/- SEM 24 microgram/day), and give a basis for selecting the doses of calcitonin which can be considered physiological.

Comparison of acute effects of 1.25- and 24.25-dihydroxy-vitamin D3 in normal subjects.

Effects of small iv doses of 1.25-dihydroxy- and 24.25-dihydroxy-vitamin D3 (a microgram) were studied in 10 normal subjects. Injection of 1.25 (OH)2D3 was associated with small but significant increases in plasma calcium and phosphate but plasma levels of immunoreactive parathyroid hormone (iPTH) and calcitonin (iCT) did not change. The administration of 24.25 (OH)2D3 was associated with comparable decreases in plasma calcium and a small and transient decrease in plasma iPTH. Plasma levels of iCT did not change. 24.25 (OH)2D3 also significantly increased glomerular filtration rate and decreased the urinary excretion of noradrenaline, in contrast to 1.25 (OH)2D3 which had no effect on these variables. The rapid infusion of calcium significantly decreased levels of iPTH. We conclude that small doses of 1.25 (OH)2D3 and 24.25 (OH)2D3 have little, if any, direct effect on the secretion of PTH and CT in man.