Fitness Trade-Offs in Competence Differentiation of Bacillus subtilis.

In the stationary phase, Bacillus subtilis differentiates stochastically and transiently into the state of competence for transformation (K-state). The latter is associated with growth arrest, and it is unclear how the ability to develop competence is stably maintained, despite its cost. To quantify the effect differentiation has on the competitive fitness of B. subtilis, we characterized the competition dynamics between strains with different probabilities of entering the K-state. The relative fitness decreased with increasing differentiation probability both during the stationary phase and during outgrowth. When exposed to antibiotics inhibiting cell wall synthesis, transcription, and translation, cells that differentiated into the K-state showed a selective advantage compared to differentiation-deficient bacteria; this benefit did not require transformation. Although beneficial, the K-state was not induced by sub-MIC concentrations of antibiotics. Increasing the differentiation probability beyond the wt level did not significantly affect the competition dynamics with transient antibiotic exposure. We conclude that the competition dynamics are very sensitive to the fraction of competent cells under benign conditions but less sensitive during antibiotic exposure, supporting the picture of stochastic differentiation as a fitness trade-off.

Oxygen governs gonococcal microcolony stability by enhancing the interaction force between type IV pili.

The formation of small bacterial clusters, called microcolonies, is the first step towards the formation of bacterial biofilms. The human pathogen Neisseria gonorrhoeae requires type IV pili (T4P) for microcolony formation and for surface motility. Here, we investigated the effect of oxygen on the dynamics of microcolony formation. We found that an oxygen concentration exceeding 3 µM is required for formation and maintenance of microcolonies. Depletion of proton motive force triggers microcolony disassembly. Disassembly of microcolonies is actively driven by T4P retraction. Using laser tweezers we showed that under aerobic conditions T4P-T4P interaction forces exceed 50 pN. Under anaerobic conditions T4P-T4P interaction is severely inhibited. We conclude that oxygen is required for gonococcal microcolony formation by enhancing pilus-pilus interaction.

Monitoring of acute myeloid leukemia patients after allogeneic stem cell transplantation employing semi-automated CD34+ donor cell chimerism analysis.

Determination of donor chimerism profiles in blood or bone marrow from patients with allogeneic stem cell transplantation (SCT) is useful for monitoring engraftment or predicting relapse, when specific molecular markers are lacking. CD34+ donor cell chimerism (DCC) analysis in peripheral blood samples from CD34+ acute myeloid leukemia (AML) and myleodysplastic syndrome (MDS) patients proved to be a highly sensitive diagnostic tool that is useful to detect imminent relapse significantly earlier compared to total white blood cell donor cell chimerism monitoring. However, flow-cytometric enrichment of CD34+ cells requires high efforts to human resources and equipment. We present a novel semi-automated CD34+ DCC analysis procedure-employing a magnetic cell-enrichment device, DNA extraction, and short tandem repeat profiling-without the need for flow-cytometric cell sorting. Monitoring 85 patients with AML and MDS over a period of 4 years 24 relapses were detected. Semi-automated peripheral blood CD34+ DCC was diminished below 80 % in all cases of systemic relapse. Significant decrease of the CD34+ DCC value was detected 29-42 days before overt cytological relapse. Our method provides a rapid and sensitive tool for monitoring AML and MDS patients after allogeneic SCT with regard to engraftment and early detection of relapse. Here, we propose a novel semi-automated procedure for CD34+ DCC analysis after allogeneic SCT that is simple, reliable, and therefore applicable in all hematologic laboratories.

α4 integrin levels on mobilized peripheral blood stem cells predict rapidity of engraftment in patients receiving autologous stem cell transplantation.

Rapidness of leukocyte engraftment in patients receiving peripheral blood stem cell transplantation is clinically important because the risk of fatal opportunistic infections increases with time to engraftment. Adhesion receptor molecules on hematopoietic stem cells (HSCs) have been shown to modulate homing and engraftment of HSCs. Therefore, we correlated expression levels of α4 (CD49d) and α6 (CD49f) integrins in the CD34(+) HSC compartment with time to engraftment. Leukapheresis products from 103 patients were retrospectively analyzed for CD34, CD38, CD3, CD49f, and CD49d surface molecules by multiparameter flow cytometry. High expression levels of α4 integrin, but not α6 integrin on CD34(+) cells, were associated with regular engraftment of leukocytes (days 8-19), whereas low surface expression correlated with delayed recovery (> 19 days; P < .0005). We show that α4 integrin expression levels on HSCs in leukapheresis products predict the engraftment capacity of mobilized peripheral blood stem cells in peripheral blood stem cell transplantation patients.

Comparison of ATP-binding cassette transporter interactions with the tyrosine kinase inhibitors imatinib, nilotinib, and dasatinib.

Although the development of tyrosine kinase inhibitors (TKIs) to control the unregulated activity of BCR-ABL revolutionized the therapy of chronic myeloid leukemia, resistance to TKIs is a clinical reality. Among the postulated mechanisms of resistance is the overexpression of ATP-binding cassette (ABC) transporters, such as P-glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2), which mediate reduced intracellular drug accumulation. We compared the interactions of the TKIs imatinib, nilotinib, and dasatinib with ABCB1 and ABCG2 in ex vivo and in vitro systems. The TKIs inhibited rhodamine 123 and Hoechst 33342 efflux mediated by endogenous expression of the transporters in murine and human hematopoietic stem cells with potency order nilotinib >> imatinib >> dasatinib. Studies with ABCB1-, ABCG2-, and ABCC1-transfected human embryonic kidney 293 cells verified that nilotinib was the most potent inhibitor of ABCB1 and ABCG2. Cytotoxicity assays in stably transduced K562-ABCG2 and K562-ABCB1 cells confirmed that the TKIs were also substrates for the two transporters. Like imatinib, both nilotinib and dasatinib decreased ABCG2 surface expression in K562-ABCG2 cells. Finally, we found that all TKIs were able to compete labeling of ABCB1 and ABCG2 by the photo-cross-linkable prazosin analog [(125)I]iodoarylazidoprazosin, suggesting interaction at the prazosin-binding site of both proteins. Our experiments support the hypothesis that all three TKIs are substrates of ABC transporters and that, at higher concentrations, TKIs overcome transporter function. Taken together, the results suggest that therapeutic doses of imatinib and nilotinib may diminish the potential of ABCB1 and ABCG2 to limit oral absorption or confer resistance. Clinical data are required to definitively answer the latter question.

Overlapping functions of argonaute proteins in patterning and morphogenesis of Drosophila embryos.

Argonaute proteins are essential components of the molecular machinery that drives RNA silencing. In Drosophila, different members of the Argonaute family of proteins have been assigned to distinct RNA silencing pathways. While Ago1 is required for microRNA function, Ago2 is a crucial component of the RNA-induced silencing complex in siRNA-triggered RNA interference. Drosophila Ago2 contains an unusual amino-terminus with two types of imperfect glutamine-rich repeats (GRRs) of unknown function. Here we show that the GRRs of Ago2 are essential for the normal function of the protein. Alleles with reduced numbers of GRRs cause specific disruptions in two morphogenetic processes associated with the midblastula transition: membrane growth and microtubule-based organelle transport. These defects do not appear to result from disruption of siRNA-dependent processes but rather suggest an interference of the mutant Ago2 proteins in an Ago1-dependent pathway. Using loss-of-function alleles, we further demonstrate that Ago1 and Ago2 act in a partially redundant manner to control the expression of the segment-polarity gene wingless in the early embryo. Our findings argue against a strict separation of Ago1 and Ago2 functions and suggest that these proteins act in concert to control key steps of the midblastula transition and of segmental patterning.

Functional analysis of the glutathione S-transferase 3 from Onchocerca volvulus (Ov-GST-3): a parasite GST confers increased resistance to oxidative stress in Caenorhabditis elegans.

This study examined the genomic organisation of the coding region of the glutathione S-transferase 3 (Ov-GST-3) from the human parasitic nematode Onchocerca volvulus; alternative splicing leads to three different transcripts (Ov-GST-3/1; Ov-GST-3/2 and Ov-GST-3/3). Since the expression of Ov-GST-3 is inducible by oxidative stress, it is assumed that it is involved in the defense against reactive oxygen species (ROS) resulting from cellular metabolism. Furthermore, we suggest that Ov-GST-3 plays an important role in the protection of the parasite against ROS derived from the host's immune system. To experimentally investigate these speculations, we generated Caenorhabditis elegans lines transgenic for Ov-GST-3 (AK1) and examined their resistance to artificially generated ROS. The AK1 worms (extrachromosomal and integrated lines) were found to be much more resistant to internal (juglone) and external (hypoxanthine/xanthine oxidase) oxidative stress than wild-type C.elegans worms. RNA interference experiments targeted to the Ov-GST-3 transcripts resulted in decreased resistance, confirming that this effect is due to the transgenic expression of Ov-GST-3. These results clearly demonstrate that the Ov-GST-3 gene confers an increased resistance to oxidative stress. This study also shows the applicability of C.elegans as a model organism for the functional characterization of genes from (parasitic) nematode species which are not accessible to genetic manipulations.