Using genomic inbreeding coefficient estimates for homozygosity mapping of rare recessive traits: application to Taybi-Linder syndrome

The use of inbred patients whose exact genealogy may not be available is of primary interest in mapping genes involved in rare recessive diseases. We show here that this can be achieved by estimating inbreeding coefficients from the patients' genomic information and using these estimates to perform homozygosity mapping. We show the interest of the approach by mapping a gene for Taybi-Linder syndrome to chromosome 2q, with the use of a key patient with no genealogical information.     

Hydrophobic substitutions in the first residue of the CRAC segment of the gp41 protein of HIV

We investigated the peptides N-acetyl-AWYIK-amide and N-acetyl-VWYIK-amide corresponding to single amino acid substitutions in LWYIK, a segment found in the gp41 protein of HIV and believed to play a role in sequestering this protein to a cholesterol-rich domain in the membrane. The effects of these peptides on the thermotropic phase transitions of 1-stearoyl-2-oleoylphosphatidylcholine (SOPC) and mixtures of SOPC and cholesterol were intermediate between that having the wild-type sequence (LWYIK) and another (IWYIK), the least active peptide previously studied. This correlated with results from studies of single mutations in the gp41 protein of HIV-1, in which L679 of the LWYIK segment is replaced with either A or V, measuring the capability of TZM-BL HeLa-based HIV-1 indicator cells to form syncytia. The peptides were also comparatively analyzed in silico. All together, the results suggest that the mode of interaction of this region of gp41 with the polar heads of membrane lipids contributes to its cholesterol selectivity and that this is somehow related to the biological activity of the viral glycoprotein.     

REMARKABLE CONSERVATION OF INTERNALLY TRANSCRIBED SPACER SEQUENCES OF ARTHROSPIRA (“SPIRULINA” ) (CYANOPHYCEAE,CYANOBACTERIA) STRAINS FROM FOUR CONTINENTS AND OF RECENT AND 30‐YEAR‐OLD DRIED SAMPLES FROM AFRICA1

The internally transcribed spacer (ITS) sequences of 21 Arthrospira clonal strains from four continents and assigned to four different species (A. platensis, A. maxima, A. fusiformis, A. indica) in the culture collections were determined. Two main clusters, I and II, were differentiated by 49 positions out of 475 nt or 477 nt, respectively. Each cluster was further subdivided into two subclusters. Subclusters I.A and I.B were separated by two substitutions, whereas subclusters II.A and II.B were distinguished by four substitutions. After direct sequencing of the PCR products, three dried samples from Chad aged between 3 months and 35 years yielded a sequence belonging to subcluster I.A, as did a recent commercial product. The strains grown in production plants belonged to the same (sub)clusters as strains from culture collections, mainly I.A and II. PCR primers specific for each cluster and subcluster were designed and tested with crude cell lysates of Arthrospira strains. One dried sample (“dihé” 1) and a herbarium sample from Lake Sonachi (Kenya) only contained I.A sequences, whereas the commercial product was a mixture of the four genotypes and the other two dried samples contained minor polymorphisms characteristic of different clusters. Five clonal Arthrospira strains, thought to be duplicates, showed the simultaneous presence of the two forms of the four diagnostic positions that distinguish subclusters genotype II.A and genotype II.B. This is likely to be caused by multiple copies of the rDNA operon, in a intermediate stage of homogenization between subcluster II.A and subcluster II.B. The high conservation of ITS sequences is in contrast with the assignment to four different species, the great morphological variability of the strains, and their wide geographic distribution.     

Chaos in biology.

This paper presents a brief and pedagogical account of the relevance of chaos theory in biology. A few caveats to avoid misleading interpretations are underlined, for instance the required determinism and consistency of the experimental time series. The selective advantage offered by a properly controlled chaotic dynamics is discussed on the examples of cardiac rhythm and brain dynamics.     

Long-term evolution of endocrine disorders and effect of GH therapy in 35 patients with pituitary stalk interruption syndrome

We report long-term evolution of endocrine functions and the results of GH treatment in 35 patients (26 male and 9 female) with pituitary stalk interruption. At diagnosis, mean chronological age was 4.8 +/- 2.7 years, mean SDS for height -3.1 +/- 0.8 with a bone age retardation of 2.3 +/- 1.3 years and a mean SDS for growth velocity of -0.5 +/- 1.1; 80% presented complete GH deficiency (GHD) and 20% partial GHD; thyroid deficiency was present in 47.1% of children with complete GHD but absent in all partial GHD. Diagnosis was made during the first months of life in only 2 patients while 23% presented with severe neonatal distress; neonatal signs were only observed in the group with pituitary height below 2 mm (45.7% of patients). GHD was isolated in 40.6% of patients below 10 years while multiple hormone deficiencies was consistent at completion of growth in all patients. Height gain was significantly higher in patients who started GH treatment before 4 years (p = 0.002). GH treatment is very effective: in 13 patients, final height was -0.4 +/- 1.0, total height gain 3.2 +/- 1.2 and distance to target height -0.3 +/- 1.6 SDS.     

Specific ablation of the apoptotic functions of cytochrome C reveals a differential requirement for cytochrome C and Apaf-1 in apoptosis

As components of the apoptosome, a caspase-activating complex, cytochrome c (Cyt c) and Apaf-1 are thought to play critical roles during apoptosis. Due to the obligate function of Cyt c in electron transport, its requirement for apoptosis in animals has been difficult to establish. We generated "knockin" mice expressing a mutant Cyt c (KA allele), which retains normal electron transfer function but fails to activate Apaf-1. Most KA/KA mice displayed embryonic or perinatal lethality caused by defects in the central nervous system, and surviving mice exhibited impaired lymphocyte homeostasis. Although fibroblasts from the KA/KA mice were resistant to apoptosis, their thymocytes were markedly more sensitive to death stimuli than Apaf-1(-/-) thymocytes. Upon treatment with gamma irradiation, procaspases were efficiently activated in apoptotic KA/KA thymocytes, but Apaf-1 oligomerization was not observed. These studies indicate the existence of a Cyt c- and apoptosome-independent but Apaf-1-dependent mechanism(s) for caspase activation.     

Polar acyclic diterpenoids from Bifurcaria bifurcata (Fucales, Phaeophyta)

From the lipophilic extract of the brown alga Bifurcaria bifurcata collected off the Atlantic coast of Southern Brittany (Quiberon, France), five polar linear diterpenoids have been isolated. These metabolites have been identified as hydroxylated derivatives of 13-oxo- and 13-hydroxygeranylgeraniol. Their structures were characterized on the basis of chemical and spectral evidence including two-dimensional NMR experiments and mass spectrometric techniques. The absolute configuration of the 13-position has been determined, for the 13-hydroxygeranylgeraniol derivatives, to be R by means of a modified Mosher's method and therefore that of 13-hydroxygeranylgeraniol (eleganediol) has been revised. Along with these compounds, three related known geranylgeraniol derivatives were also identified, and these data were used for chemotaxonomical purposes.     

Anchorage of synthetic peptides onto liposomes via hydrazone and alpha-oxo hydrazone bonds. preliminary functional investigations

Synthetic peptidoliposomes have been designed and prepared according to a chemoselective ligation. Two aldehyde-functionalized lipidic anchors were synthesized and incorporated into the lipidic bilayers of unilamellar liposomes during their preparation. Complementary hydrazino acetyl peptides were synthesized on the solid phase using N,N',N'-tri(tert-butyloxycarbonyl)-hydrazino acetic acid and further coupled to the aldehyde groups displayed at the surface of the vesicles. Coupling yields were measured by amino acid hydrolysis following total acid hydrolysis. The ligation methodology proved superior to the simple insertion of lipopeptides, which was performed for comparison in terms of yields, implementation, and reproducibility. To check whether the grafted-peptides were accessible and functional, cytoplasmic sequences of LAMP protein (lysosomal associated membrane protein), which is involved in intracellular membrane trafficking, have been selected. Using this model, we demonstrated in vitro the specific interaction of the synthetic LAMP-peptidoliposomes with the cytoplasmic adaptor protein AP-3, a result that contributes to the understanding of protein sorting in cells. Thus, these results clearly indicate the usefulness of such peptidoliposomes, easily prepared by hydrazone chemoselective ligation, as a tool for biological investigation.     

Fusogenic Alzheimer's peptide fragment Abeta (29-42) in interaction with lipid bilayers: secondary structure, dynamics, and specific interaction with phosphatidyl ethanolamine polar heads as revealed by solid-state NMR

The interaction of the native Alzheimer's peptide C-terminal fragment Abeta (29-42), and two mutants (G33A and G37A) with neutral lipid bilayers made of POPC and POPE in a 9:1 molar ratio was investigated by solid-state NMR. This fragment and the lipid composition were selected because they represent the minimum requirement for the fusogenic activity of the Alzheimer's peptide. The chemical shifts of alanine methyl isotropic carbon were determined by MAS NMR, and they clearly demonstrated that the major form of the peptide equilibrated in membrane is not in a helical conformation. (2)H NMR, performed with acyl chain deuterated POPC, demonstrated that there is no perturbation of the acyl chain's dynamics and of the lipid phase transition temperature. (2)H NMR, performed with alanine methyl-deuterated peptide demonstrated that the peptide itself has a limited mobility below and above the lipid phase transition temperature (molecular order parameter equal to 0.94). MAS (31)P NMR revealed a specific interaction with POPE polar head as seen by the enhancement of POPE phosphorus nuclei T(2) relaxation. All these results are in favor of a beta-sheet oligomeric association of the peptide at the bilayer interface, preferentially recruiting phosphatidyl ethanolamine polar heads.     

Role of the lid hydrophobicity pattern in pancreatic lipase activity

Pancreatic lipase is a soluble globular protein that must undergo structural modifications before it can hydrolyze oil droplets coated with bile salts. The binding of colipase and movement of the lipase lid open access to the active site. Mechanisms triggering lid mobility are unclear. The *KNILSQIVDIDGI* fragment of the lid of the human pancreatic lipase is predicted by molecular modeling to be a tilted peptide. Tilted peptides are hydrophobicity motifs involved in membrane fusion and more globally in perturbations of hydrophobic/hydrophilic interfaces. Analysis of this lid fragment predicts no clear consensus of secondary structure that suggests that its structure is not strongly sequence determined and could vary with environment. Point mutations were designed to modify the hydrophobicity profile of the [240-252] fragment and their consequences on the lipase-mediated catalysis were tested. Two mutants, in which the tilted peptide motif was lost, also have poor activity on bile salt-coated oil droplets and cannot be reactivated by colipase. Conversely, one mutant in which a different tilted peptide is created retains colipase dependence. These results suggest that the tilted hydrophobicity pattern of the [240-252] fragment is neither important for colipase binding to lipase, nor for interfacial binding but is important to trigger the maximal catalytic efficiency of lipase in the presence of bile salt.