Green Tea Polyphenols Rescue of Brain Defects Induced by Overexpression of DYRK1A

Individuals with partial HSA21 trisomies and mice with partial MMU16 trisomies containing an extra copy of the DYRK1A gene present various alterations in brain morphogenesis. They present also learning impairments modeling those encountered in Down syndrome. Previous MRI and histological analyses of a transgenic mice generated using a human YAC construct that contains five genes including DYRK1A reveal that DYRK1A is involved, during development, in the control of brain volume and cell density of specific brain regions. Gene dosage correction induces a rescue of the brain volume alterations. DYRK1A is also involved in the control of synaptic plasticity and memory consolidation. Increased gene dosage results in brain morphogenesis defects, low BDNF levels and mnemonic deficits in these mice. Epigallocatechin gallate (EGCG) — a member of a natural polyphenols family, found in great amount in green tea leaves — is a specific and safe DYRK1A inhibitor. We maintained control and transgenic mice overexpressing DYRK1A on two different polyphenol-based diets, from gestation to adulthood. The major features of the transgenic phenotype were rescued in these mice

Brain Phenotype of Transgenic Mice Overexpressing Cystathionine β-Synthase

The cystathionine β-synthase (CBS) gene, located on human chromosome 21q22.3, is a good candidate for playing a role in the Down Syndrome (DS) cognitive profile: it is overexpressed in the brain of individuals with DS, and it encodes a key enzyme of sulfur-containing amino acid (SAA) metabolism, a pathway important for several brain physiological processes.Here, we have studied the neural consequences of CBS overexpression in a transgenic mouse line (60.4P102D1) expressing the human CBS gene under the control of its endogenous regulatory regions. These mice displayed a ∼2-fold increase in total CBS proteins in different brain areas and a ∼1.3-fold increase in CBS activity in the cerebellum and the hippocampus. No major disturbance of SAA metabolism was observed, and the transgenic mice showed normal behavior in the rotarod and passive avoidance tests. However, we found that hippocampal synaptic plasticity is facilitated in the 60.4P102D1 line.We demonstrate that CBS overexpression has functional consequences on hippocampal neuronal networks. These results shed new light on the function of the CBS gene, and raise the interesting possibility that CBS overexpression might have an advantageous effect on some cognitive functions in DS

Early thymic T cell development in young transgenic mice overexpressing human Cu/Zn superoxide dismutase, a model of Down syndrome.: Early thymic development in SOD1 transgenic mice.

Previous studies have shown that transgenic mice overexpressing Cu/Zn superoxide dismutase, a model of Down syndrome, exhibit premature thymic involution. We have performed a flow cytometry analysis of the developing thymus in these homozygous transgenic mice (hSOD1/hSOD1: Tg-SOD). Longitudinal follow-up analysis from day 3 to day 280 showed an early thymic development in Tg-SOD mice compared with controls. This early thymic development was associated with an increased migration of mature T cells to peripheral lymphoid organs. BrdU labeling showed no difference between Tg-SOD and control mice, confirming that the greater number of peripheral T cells in Tg-SOD mice was not due to extensive proliferation of these cells but rather to a greater pool of emigrant T cells in Tg-SOD

High-resolution whole-genome analysis of sister-chromatid contacts

International audienceSister-chromatid cohesion describes the orderly association of newly replicated DNA molecules behind replication forks. It plays an essential role in the maintenance and faithful transmission of genetic information. Cohesion is created by DNA topological links and proteinaceous bridges, whose formation and deposition could be potentially affected by many processes. Current knowledge on cohesion has been mainly gained by fluorescence microscopy observation. However, the resolution limit of microscopy and the restricted number of genomic positions that can be simultaneously visualized considerably hampered progress. Here, we present a high-throughput methodology to monitor sister-chromatid contacts (Hi-SC2). Using the multi-chromosomal Vibrio cholerae bacterium as a model, we show that Hi-SC2 permits to monitor local variations in sister-chromatid cohesion at a high resolution over a whole genome

Late assembly of the Vibrio cholerae cell division machinery postpones septation to the last 10% of the cell cycle

Bacterial cell division is a highly regulated process, which involves the formation of a complex apparatus, the divisome, by over a dozen proteins. In the few model bacteria in which the division process was detailed, divisome assembly occurs in two distinct steps: a few proteins, including the FtsZ tubulin-like protein, form a membrane associated contractile ring, the Z-ring, at ~30% of the cell cycle. The Z-ring serves as a scaffold for the recruitment of a second series of proteins, including integral membrane and periplasmic cell wall remodelling enzymes, at ~50% of the cell cycle. Actual septation occupies most of the remaining half of the cell cycle. In contrast, we present evidence suggesting that early pre-divisional Z-rings form between 40 and 50% of the cell cycle and mature into fully assembled divisome at about 80% of the cell cycle in Vibrio cholerae. Thus, actual septation is restricted to a very short amount of time. Our results further suggest that late assembly of the divisome probably helps maintain the asymmetric polar organisation of V. cholerae cells by limiting the accumulation of a cell pole marker, HubP, at the nascent cell poles

CTXφ Replication Depends on the Histone-Like HU Protein and the UvrD Helicase.

International audienceThe Vibrio cholerae bacterium is the agent of cholera. The capacity to produce the cholera toxin, which is responsible for the deadly diarrhea associated with cholera epidemics, is encoded in the genome of a filamentous phage, CTXφ. Rolling-circle replication (RCR) is central to the life cycle of CTXφ because amplification of the phage genome permits its efficient integration into the genome and its packaging into new viral particles. A single phage-encoded HUH endonuclease initiates RCR of the proto-typical filamentous phages of enterobacteriaceae by introducing a nick at a specific position of the double stranded DNA form of the phage genome. The rest of the process is driven by host factors that are either essential or crucial for the replication of the host genome, such as the Rep SF1 helicase. In contrast, we show here that the histone-like HU protein of V. cholerae is necessary for the introduction of a nick by the HUH endonuclease of CTXφ. We further show that CTXφ RCR depends on a SF1 helicase normally implicated in DNA repair, UvrD, rather than Rep. In addition to CTXφ, we show that VGJφ, a representative member of a second family of vibrio integrative filamentous phages, requires UvrD and HU for RCR while TLCφ, a satellite phage, depends on Rep and is independent from HU

Fast growth conditions uncouple the final stages of chromosome segregation and cell division in Escherichia coli

Homologous recombination between the circular chromosomes of bacteria can generate chromosome dimers. They are resolved by a recombination event at a specific site in the replication terminus of chromosomes, dif, by dedicated tyrosine recombinases. The reaction is under the control of a cell division protein, FtsK, which assembles into active DNA pumps at mid-cell during septum formation. Previous studies suggested that activation of Xer recombination at dif was restricted to chromosome dimers in Escherichia coli but not in Vibrio cholerae, suggesting that FtsK mainly acted on chromosome dimers in E. coli but frequently processed monomeric chromosomes in V. cholerae. However, recent microscopic studies suggested that E. coli FtsK served to release the MatP-mediated cohesion and/or cell division apparatus-interaction of sister copies of the dif region independently of chromosome dimer formation. Here, we show that these apparently paradoxical observations are not linked to any difference in the dimer resolution machineries of E. coli and V. cholerae but to differences in the timing of segregation of their chromosomes. V. cholerae harbours two circular chromosomes, chr1 and chr2. We found that whatever the growth conditions, sister copies of the V. cholerae chr1 dif region remain together at mid-cell until the onset of constriction, which permits their processing by FtsK and the activation of dif-recombination. Likewise, sister copies of the dif region of the E. coli chromosome only separate after the onset of constriction in slow growth conditions. However, under fast growth conditions the dif sites separate before constriction, which restricts XerCD-dif activity to resolving chromosome dimers

The TLCΦ satellite phage harbors a Xer recombination activation factor

The circular chromosomes of bacteria can be concatenated into dimers by homologous recombination. Dimers are solved by the addition of a cross-over at a specific chromosomal site, dif, by 2 related tyrosine recombinases, XerC and XerD. Each enzyme catalyzes the exchange of a specific pair of strands. Some plasmids exploit the Xer machinery for concatemer resolution. Other mobile elements exploit it to integrate into the genome of their host. Chromosome dimer resolution is initiated by XerD. The reaction is under the control of a cell-division protein, FtsK, which activates XerD by a direct contact. Most mobile elements exploit FtsK-independent Xer recombination reactions initiated by XerC. The only notable exception is the toxin-linked cryptic satellite phage of Vibrio cholerae, TLCΦ, which integrates into and excises from the dif site of the primary chromosome of its host by a reaction initiated by XerD. However, the reaction remains independent of FtsK. Here, we show that TLCΦ carries a Xer recombination activation factor, XafT. We demonstrate in vitro that XafT activates XerD catalysis. Correspondingly, we found that XafT specifically interacts with XerD. We further show that integrative mobile elements exploiting Xer (IMEXs) encoding a XafT-like protein are widespread in gamma- and beta-proteobacteria, including human, animal, and plant pathogens

Insights into TLCΦ lysogeny: A twist in the mechanism of IMEX integration

International audienceMany organisms have established symbiotic relationships with acquired mobile genetic elements (MGEs) integrated in their genomes (1). MGEs spread among genomes within and across microbial species through horizontal gene transfer and, once integrated into host chromosome, are disseminated vertically to the progeny, causing rapid evolution of drug resistance, pathogenicity, and virulence traits (2, 3). The MGEs that integrates into the host bacterial chromosomes (IMGEs) either carry their own DNA integration machineries or exploit machineries already existing in the host organisms for integration (4). The latter elements are of interest, in part, because of their contribution to pathogenesis, antimicrobial resistance, and other medically relevant properties (5, 6). One of the host site-specific recombination systems frequently exploited by IMGEs is the widely distributed bacterial chromosome dimer-resolving Xer recombination system, a system that recombines chromosomes at dif site located near where DNA replication terminates (7). As in all organisms, during DNA replication of bacteria, many DNA damages need to be repaired by homologous recombination reaction. For bacteria having circular chromosomes, this often generates circular dimer chromosome, causing problems when the cell divides. Hence, when a pair of unresolved chromosome dimer junctions get trapped at the closing cell division septum, the pair of dif sites with XerC and XerD recombinases bound across the recombination junction encounter FtsK DNA translocation pump, a component of the closing septum complex, whose job is to clear trapped DNA out of the septum. This encounter triggers initiation of recombination by activating XerD to carry out the first strand exchange, generating a Holliday junction recombination intermediate, which is resolved by XerC-mediated second pair of strand exchange (8). XerC is an efficient resolver of the recombination intermediate but a poor recombination initiator. Without FtsK activation, Xer remains essentially silent, avoiding formation of chromosome dimer out of 2 separable replicated … [↵][1]1Email: bhabatosh\at\thsti.res.in. [1]: #xref-corresp-1-

HU is essential for CTXϕ replication.

<p><b>(A and B)</b> Relative colony-forming ability after conjugation with a replicative form of RS2 in the indicated strains. After 3 h of conjugation, serial dilutions were plated on chloramphenicol and incubated overnight at 42°C (A) and 37°C (B). Relative colony forming units (cfu) correspond to the ratio of the number of colonies obtained in the indicated strain over the mean number of colonies obtained in ∆<i>xerC</i> cells. Results are shown in a logarithmic scale and represent the mean and standard deviation of 3 independent experiments. The detection limit of the experiment is indicated by a dotted line. <b>(C and D)</b> Colonies obtained at 37°C were re-streaked on plate and incubated overnight at 42°C (C) and 37°C (D). <b>(E)</b> Complementation assay of Δ<i>hupAB</i> cells with a pUC18 vector carrying the <i>V</i>. <i>cholerae hupA</i> gene (pUC-<i>hupA</i>) <i>or hupB</i> gene (pUC-<i>hupB</i>). RS2 was conjugated into Δ<i>xerC</i> Δ<i>hupAB</i> + pUC18, Δ<i>xerC</i> Δ<i>hupAB</i> + pUC-<i>hupA</i> and Δ<i>xerC</i> Δ<i>hupAB</i> + pUC-<i>hupB</i>. The conjugants were then streaked on a plate supplemented with ampicillin and chloramphenicol. The plate was incubated overnight at 37°C.</p