Mandibuloacral dysplasia is caused by a mutation in LMNA-encoding lamin A/C

Mandibuloacral dysplasia (MAD) is a rare autosomal recessive disorder, characterized by postnatal growth retardation, craniofacial anomalies, skeletal malformations, and mottled cutaneous pigmentation. The LMNA gene encoding two nuclear envelope proteins (lamins A and C [lamin A/C]) maps to chromosome 1q21 and has been associated with five distinct pathologies, including Dunnigan-type familial partial lipodystrophy, a condition that is characterized by subcutaneous fat loss and is invariably associated with insulin resistance and diabetes. Since patients with MAD frequently have partial lipodystrophy and insulin resistance, we hypothesized that the disease may be caused by mutations in the LMNA gene. We analyzed five consanguineous Italian families and demonstrated linkage of MAD to chromosome 1q21, by use of homozygosity mapping. We then sequenced the LMNA gene and identified a homozygous missense mutation (R527H) that was shared by all affected patients. Patient skin fibroblasts showed nuclei that presented abnormal lamin A/C distribution and a dysmorphic envelope, thus demonstrating the pathogenic effect of the R527H LMNA mutation.     

DNA2 drives processing and restart of reversed replication forks in human cells

Accurate processing of stalled or damaged DNA replication forks is paramount to genomic integrity and recent work points to replication fork reversal and restart as a central mechanism to ensuring high-fidelity DNA replication. Here, we identify a novel DNA2- and WRN-dependent mechanism of reversed replication fork processing and restart after prolonged genotoxic stress. The human DNA2 nuclease and WRN ATPase activities functionally interact to degrade reversed replication forks with a 5′-to-3′ polarity and promote replication restart, thus preventing aberrant processing of unresolved replication intermediates. Unexpectedly, EXO1, MRE11, and CtIP are not involved in the same mechanism of reversed fork processing, whereas human RECQ1 limits DNA2 activity by preventing extensive nascent strand degradation. RAD51 depletion antagonizes this mechanism, presumably by preventing reversed fork formation. These studies define a new mechanism for maintaining genome integrity tightly controlled by specific nucleolytic activities and central homologous recombination factors.     

Photochemistry and DNA-affinity of some pyrimidine-substituted styryl-azinium iodides

The relaxation properties of the excited states of three iodides of trans-1,2-diarylethene analogues (where one aryl group is a methylpyridinium, methylquinolinium or dimethylimidazolium group and the other one is a phenyl ring para-substituted by a pyrimidine ring) have been investigated in buffered (pH = 7) aqueous solution. As found in previous works for several analogues, these quaternized salts undergo efficient trans→cis photoisomerization while the yield of the radiative deactivation is very small at room temperature. The solvent effect on the spectral behaviour indicates the occurrence of intramolecular charge transfer which can induce interesting non-linear optical properties. The results of a study of the interactions of these salts with DNA, which might affect the cell metabolism, showed a relatively modest binding affinity for the pyridinium and imidazolium salts and a more substantial affinity for the quinolinium analogue. The formation of ligand-DNA complexes affects only slightly the radiative relaxation yield while leading to a relevant reduction of the isomerization yield. Measurements of the linear dichroism behaviour of the three compounds and comparison with three analogues bearing furan or thienyl groups, which have been found to display different affinity with DNA in previous works, gave interesting information on the nature of the ligand-DNA binding of these compounds.     

Unbalanced oxidant-antioxidant status and its effects in pediatric diseases

Oxidative stress results from a disparity between the generation of reactive oxygen species and the antioxidant ability of the organism. The alteration of the oxidant-antioxidant system brings in adults an effective state of imbalance, which may influence the pathogenesis of many diseases. Oxidative stress also plays a pivotal role in the progression of various pathologies in childhood, through a manipulation of regulatory proteins. In fact, several studies have demonstrated that an unbalanced oxidant-antioxidant status is able to determine toxic effects even during infancy. Therefore, the aim of this review was to summarize current knowledge about the dynamic relationship between oxidative stress and systemic diseases during childhood. In order to better understand these complex mechanisms, a comprehensive review of the literature was done, focusing mainly on pre-pubertal children. In fact, this age-group offers a unique opportunity to exclude confounding factors, especially those related to the metabolic effects induced by puberty. Early identification of these very young patients should be aimed at minimizing the degree of oxidative damage. Only by achieving early diagnosis, will it be possible to identify those children who could benefit from specific therapeutic approaches targeting oxidative stress.     

Flavonoids from the leaves of Cyclanthera pedata: two new malonyl derivatives

Reversed-phase HPLC coupled with electrospray MS has been used for the simultaneous separation and determination of flavonoid metabolites in leaves of Cyclanthera pedata, an edible Peruvian plant mainly used in South America for its anti-inflammatory, hypoglycaemic and hypocholesterolaemic properties. The flavonoid content of the leaves of C. pedata was compared qualitatively and quantitatively with that of the fruits. The isolation and structural characterisation by MS and NMR of two new minor components of the fruits, namely, 6-C-fucopyranosyl-(3-malonyl)-chrysin and 6-C-fucopyranosyl-(4-malonyl)-chrysin, are described.