Dysfunctional telomeres in primary cells from Fanconi anemia FANCD2 patients

© 2012 Joksic et al. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.This article has been made available through the Brunel Open Access Publishing Fund.Background: Fanconi anemia (FA) is characterized by sensitivity to DNA cross-linking agents, mild cellular, and marked clinical radio sensitivity. In this study we investigated telomeric abnormalities of non-immortalized primary cells (lymphocytes and fibroblasts) derived from FA patients of the FA-D2 complementation group, which provides a more accurate physiological assessment than is possible with transformed cells or animal models. Results: We analyzed telomere length, telomere dysfunction-induced foci (TIFs), sister chromatid exchanges (SCE), telomere sister chromatid exchanges (T-SCE), apoptosis and expression of shelterin components TRF1 and TRF2. FANCD2 lymphocytes exhibited multiple types of telomeric abnormalities, including premature telomere shortening, increase in telomeric recombination and aberrant telomeric structures ranging from fragile to long-string extended telomeres. The baseline incidence of SCE in FANCD2 lymphocytes was reduced when compared to control, but in response to diepoxybutane (DEB) the 2-fold higher rate of SCE was observed. In contrast, control lymphocytes showed decreased SCE incidence in response to DEB treatment. FANCD2 fibroblasts revealed a high percentage of TIFs, decreased expression of TRF1 and invariable expression of TRF2. The percentage of TIFs inversely correlated with telomere length, emphasizing that telomere shortening is the major reason for the loss of telomere capping function. Upon irradiation, a significant decrease of TIFs was observed at all recovery times. Surprisingly, a considerable percentage of TIF positive cells disappeared at the same time when incidence of γ-H2AX foci was maximal. Both FANCD2 leucocytes and fibroblasts appeared to die spontaneously at higher rate than control. This trend was more evident upon irradiation; the percentage of leucocytes underwent apoptosis was 2.59- fold higher than that in control, while fibroblasts exhibited a 2- h delay before entering apoptosis. Conclusion: The results of our study showed that primary cells originating from FA-D2 patients display shorten telomeres, elevated incidence of T-SCEs and high frequency of TIFs. Disappearance of TIFs in early response to irradiation represent distinctive feature of FANCD2 cells that should be examined further.This article is made available through the Brunel Open Access Publishing Fund. This work was supported by the Ministry of Education and Science of the Republic of Serbia (Project No.173046)

Mosaicism for combined tetrasomy of chromosomes 8 and 18 in a dysmorphic child: A result of failed tetraploidy correction?

<p>Abstract</p> <p>Background</p> <p>Mosaic whole-chromosome tetrasomy has not previously been described as a cause of fetal malformations.</p> <p>Case presentation</p> <p>In a markedly dysmorphic child with heart malformations and developmental delay, CGH analysis of newborn blood DNA suggested a 50% dose increase of chromosomes 8 and 18, despite a normal standard karyotype investigation. Subsequent FISH analysis revealed leukocytes with four chromosomes 8 and four chromosomes 18. The child's phenotype had resemblance to both mosaic trisomy 8 and mosaic trisomy 18. The double tetrasomy was caused by mitotic malsegregation of all four chromatids of both chromosome pairs. A possible origin of such an error is incomplete correction of a tetraploid state resulting from failed cytokinesis or mitotic slippage during early embryonic development.</p> <p>Conclusion</p> <p>This unique case suggests that embryonic cells may have a mechanism for tetraploidy correction that involves mitotic pairing of homologous chromosomes.</p

Modeling protein network evolution under genome duplication and domain shuffling

<p>Abstract</p> <p>Background</p> <p>Successive whole genome duplications have recently been firmly established in all major eukaryote kingdoms. Such <it>exponential </it>evolutionary processes must have largely contributed to shape the topology of protein-protein interaction (PPI) networks by outweighing, in particular, all <it>time-linear </it>network growths modeled so far.</p> <p>Results</p> <p>We propose and solve a mathematical model of PPI network evolution under successive genome duplications. This demonstrates, from first principles, that evolutionary conservation and scale-free topology are intrinsically linked properties of PPI networks and emerge from <it>i) </it>prevailing <it>exponential </it>network dynamics under duplication and <it>ii) asymmetric divergence </it>of gene duplicates. While required, we argue that this asymmetric divergence arises, in fact, spontaneously at the level of protein-binding sites. This supports a refined model of PPI network evolution in terms of protein domains under exponential and asymmetric duplication/divergence dynamics, with multidomain proteins underlying the combinatorial formation of protein complexes. Genome duplication then provides a powerful source of PPI network innovation by promoting local rearrangements of multidomain proteins on a genome wide scale. Yet, we show that the overall conservation and topology of PPI networks are robust to extensive domain shuffling of multidomain proteins as well as to finer details of protein interaction and evolution. Finally, large scale features of <it>direct </it>and <it>indirect </it>PPI networks of <it>S. cerevisiae </it>are well reproduced numerically with only two adjusted parameters of clear biological significance (<it>i.e</it>. network effective growth rate and average number of protein-binding domains per protein).</p> <p>Conclusion</p> <p>This study demonstrates the statistical consequences of genome duplication and domain shuffling on the conservation and topology of PPI networks over a broad evolutionary scale across eukaryote kingdoms. In particular, scale-free topologies of PPI networks, which are found to be robust to extensive shuffling of protein domains, appear to be a simple consequence of the conservation of protein-binding domains under asymmetric duplication/divergence dynamics in the course of evolution.</p

Unbalanced 18q/21q translocation in a patient previously reported as monosomy 21

We describe a patient in whom full monosomy 21 was initially assumed from routine GTG-banded karyotyping. Re-examination with chromosome painting demonstrated an unbalanced translocation between the long arms of chromosomes 18 and 21. Fluorescence in situ hybridisation (FISH) and microsatellite marker analysis revealed partial monosomy of chromosome 21 (pter-q21) and 18(q22-qter). The patient, 18 years old at the second examination, revealed multiple dysmorphic features, genital hypoplasia, dilated cerebral ventricles, muscular hypotonia and severe mental retardation. In not one out of all patients investigated postnatally in whom an initial examination had revealed monosomy 21, this could be confirmed by FISH; in all of them, re-examination detected an unbalanced rearrangement leading to only partial monosomy 21 plus partial monosomy of another chromosome to which the distal 21q segment was attached. Thus, it is still highly likely that full monosomy 21 is incompatible with intra-uterine survival

Spectrum of cystic fibrosis mutations in Serbia and Montenegro and strategy for prenatal diagnosis

We have screened 175 patients for molecular defects in the cystic fibrosis transmembrane conductance regulator (CFTR) gene using nondenaturing polyacrylamide gel electrophoresis (PAGE), denaturing gradient gel electrophoresis (DGGE), and sequencing. Six different mutations (F508del, G542X, 621+1G –&gt; T, 2789+5G –&gt; A, R1070Q, and S466X) accounted for 79.71% of CF alleles, with the F508del mutation showing a frequency of 72.28%. Another 12 mutations (R334W, 2184insA, 1507del, 1525-1G –&gt; A, E585X, R75X, MII, 457TAT –&gt; G, 574delA, 2723deiTT, A120T, and 2907delTT) covered an additional 3.36%. A novel mutation (2723deiTT) was found in one CIF patient (F508del/2723delTl’). Thus, a total of 18 mutations cover 82.57% of CF alleles. During our study, 72% of families at risk for having a CF child were found to be fully informative for prenatal diagnosis. Prenatal diagnosis was performed on 56 families; 76 analyses resulting in 16 affected, 38 carriers, and 22 healthy fetuses. These results imply that the molecular basis of CIF in Serbia and Montenegro is highly heterogeneous, as is observed in other eastern and southern European populations. Because we detected more then 80% of CFTR alleles, results could be used for planning future screening and appropriate genetic counseling programs in our country

Tetraploidy in a 26-month-old girl (cytogenetic and molecular studies)

Liveborn infants with tetraploidy are very rare in human pregnancies and usually die during the first days or months. Seven cases of liveborn infants with tetraploidy have previously been reported. Among them only two 92, XXXX infants survived for longer than 12 months. Here we report on the case of a 26-month-old girl with tetraploidy. The main clinical features of tetraploidy are facial dysmorphism, severely delayed growth and developmental delay. On the basis of molecular studies we discuss the possible origin of the additional chromosome sets in our proband. To our knowledge, this infant is the first reported case of tetraploidy who lived up to 26 months