Mycobacterium gordonae pulmonary disease associated with a continuous positive airway pressure device.

There are no formal recommendations on the proper handling and decontamination of respiratory devices for home use. We describe the case of a kidney transplant recipient who developed Mycobacterium gordonae pneumonia transmitted by his continuous positive airway pressure (CPAP) machine.

Donor-transmitted toxoplasmosis in liver transplant recipients: a case report and literature review.

Transmission of toxoplasmosis via liver transplantation is extremely uncommon. Here we report the case of a 52-year-old male liver transplant recipient who on day 32 post transplant developed pneumonia followed by respiratory failure. Donor-transmitted toxoplasmosis was confirmed as the etiology by both serologic and molecular testing. We also review all previously published cases of toxoplasmosis in the English-language adult liver transplant literature.

Intraflagellar transport balances continuous turnover of outer doublet microtubules: implications for flagellar length control.

A central question in cell biology is how cells determine the size of their organelles. Flagellar length control is a convenient system for studying organelle size regulation. Mechanistic models proposed for flagellar length regulation have been constrained by the assumption that flagella are static structures once they are assembled. However, recent work has shown that flagella are dynamic and are constantly turning over. We have determined that this turnover occurs at the flagellar tips, and that the assembly portion of the turnover is mediated by intraflagellar transport (IFT). Blocking IFT inhibits the incorporation of tubulin at the flagellar tips and causes the flagella to resorb. These results lead to a simple steady-state model for flagellar length regulation by which a balance of assembly and disassembly can effectively regulate flagellar length.

Centrioles take center stage.

Centrioles are among the most beautiful and mysterious of all cell organelles. Although the ultrastructure of centrioles has been studied in great detail ever since the advent of electron microscopy, these studies raised as many questions as they answered, and for a long time both the function and mode of duplication of centrioles remained controversial. It is now clear that centrioles play an important role in cell division, although cells have backup mechanisms for dividing if centrioles are missing. The recent identification of proteins comprising the different ultrastructural features of centrioles has proven that these are not just figments of the imagination but distinct components of a large and complex protein machine. Finally, genetic and biochemical studies have begun to identify the signals that regulate centriole duplication and coordinate the centriole cycle with the cell cycle.

Chromosome elasticity and mitotic polar ejection force measured in living Drosophila embryos by four-dimensional microscopy-based motion analysis.

BACKGROUND: Mitosis involves the interaction of many different components, including chromatin, microtubules, and motor proteins. Dissecting the mechanics of mitosis requires methods of studying not just each component in isolation, but also the entire ensemble of components in its full complexity in genetically tractable model organisms. RESULTS: We have developed a mathematical framework for analyzing motion in four-dimensional microscopy data sets that allows us to measure elasticity, viscosity, and forces by tracking the conformational movements of mitotic chromosomes. We have used this approach to measure, for the first time, the basic biophysical parameters of mitosis in wild-type Drosophila melanogaster embryos. We found that Drosophila embryo chromosomes are significantly less rigid than the much larger chromosomes of vertebrates. Anaphase kinetochore force and nucleoplasmic viscosity were comparable with previous estimates in other species. Motion analysis also allowed us to measure the magnitude of the polar ejection force exerted on chromosome arms during metaphase by individual microtubules. We find the magnitude of this force to be approximately 1 pN, a number consistent with force generation either by collision of growing microtubules with chromosomes or by single kinesin motors. CONCLUSIONS: Motion analysis allows noninvasive mechanical measurements to be made in complex systems. This approach should allow the functional effects of Drosophila mitotic mutants on chromosome condensation, kinetochore forces, and the polar ejection force to be determined.

Kinetics and regulation of de novo centriole assembly. Implications for the mechanism of centriole duplication.

BACKGROUND: Centriole duplication is a key step in the cell cycle whose mechanism is completely unknown. Why new centrioles always form next to preexisting ones is a fundamental question. The simplest model is that preexisting centrioles nucleate the assembly of new centrioles, and that although centrioles can in some cases form de novo without this nucleation, the de novo assembly mechanism should be too slow to compete with normal duplication in order to maintain fidelity of centriole duplication. RESULTS: We have measured the rate of de novo centriole assembly in vegetatively dividing cells that normally always contain centrioles. By using mutants of Chlamydomonas that are defective in centriole segregation, we obtained viable centrioleless cells that continue to divide, and find that within a single generation, 50% of these cells reacquire new centrioles by de novo assembly. This suggests that the rate of de novo assembly is approximately half the rate of templated duplication. A mutation in the VFL3 gene causes a complete loss of the templated assembly pathway without eliminating de novo assembly. A mutation in the centrin gene also reduced the rate of templated assembly. CONCLUSIONS: These results suggest that there are two pathways for centriole assembly, namely a templated pathway that requires preexisting centrioles to nucleate new centriole assembly, and a de novo assembly pathway that is normally turned off when centrioles are present.

How centrioles work: lessons from green yeast.

Centrioles are the organizing centers around which centrosomes assemble. Despite a century of study, the molecular details of centriole function and assembly remain largely unknown. Recent work has exploited the unique advantages of unicellular algae to reveal proteins that play central roles in centriole biology.

Cell division: The renaissance of the centriole.

Centrioles are located at the center of the cytoskeleton and duplicate exactly once per cell cycle. Recent studies suggest that centrioles are required for the organization of a functional centrosome and that centriole assembly requires both gamma- and delta-tubulin.

The cephalosporins.

The cephalosporins are a large group of related beta-lactam antimicrobial agents. Favorable attributes of the cephalosporins include low rates of toxicity, relatively broad spectrum of activity, and ease of administration. Various cephalosporins are effective for treatment of many conditions, including pneumonia, skin and soft tissue infections, bacteremia, and meningitis. Differences among the numerous cephalosporin antimicrobial agents are sometimes subtle; however, an understanding of these differences is essential for optimal use of these agents. As a result of widespread use of cephalosporins, bacterial resistance to these drugs is increasingly common. New, fourth-generation agents (such as cefepime) offer an alternative for the treatment of infections caused by some drug-resistant microorganisms.

Homologous chromosome pairing in Drosophila melanogaster proceeds through multiple independent initiations.

The dynamics by which homologous chromosomes pair is currently unknown. Here, we use fluorescence in situ hybridization in combination with three-dimensional optical microscopy to show that homologous pairing of the somatic chromosome arm 2L in Drosophila occurs by independent initiation of pairing at discrete loci rather than by a processive zippering of sites along the length of chromosome. By evaluating the pairing frequencies of 11 loci on chromosome arm 2L over several timepoints during Drosophila embryonic development, we show that all 11 loci are paired very early in Drosophila development, within 13 h after egg deposition. To elucidate whether such pairing occurs by directed or undirected motion, we analyzed the pairing kinetics of histone loci during nuclear cycle 14. By measuring changes of nuclear length and correlating these changes with progression of time during cycle 14, we were able to express the pairing frequency and distance between homologous loci as a function of time. Comparing the experimentally determined dynamics of pairing to simulations based on previously proposed models of pairing motion, we show that the observed pairing kinetics are most consistent with a constrained random walk model and not consistent with a directed motion model. Thus, we conclude that simple random contacts through diffusion could suffice to allow pairing of homologous sites.

Disseminated nocardiosis after allogeneic bone marrow transplantation.

Nocardia infarction is rare in bone marrow transplant recipients; only 10 cases have been reported. We describe a case of disseminated nocardiosis after allogeneic BMT with positive blood cultures and multiple cerebral and hepatosplenic abscesses.

Prophylaxis of cytomegalovirus infection in liver transplantation: a randomized trial comparing a combination of ganciclovir and acyclovir to acyclovir. NIDDK Liver Transplantation Database.

BACKGROUND: The optimal prophylactic regimen to prevent cytomegalovirus (CMV) infection and disease in orthotopic liver-transplant patients remains to be established. We tested whether a combination of intravenous ganciclovir (GCV) followed by high dosages of oral acyclovir (ACV) for 4 months provided a higher degree of protection from CMV than oral ACV alone. METHODS: One hundred sixty-seven liver-transplant recipients were randomized to receive 120 days of antiviral treatment starting at the time of transplantation consisting of either ACV 800 mg orally four times daily (n=84) or 14 days of GCV 5 mg/kg intravenously every 12 hr followed by oral ACV 800 mg four times daily (n=83). Prospective laboratory and clinical surveillance was performed to determine primary endpoints (onset of CMV infection and CMV disease) and secondary endpoints (rates of fungal and bacterial infection, allograft rejection, and survival after transplantation). One-year event rates are presented as cumulative percentages. RESULTS: During the first year after transplantation, CMV infection developed in 57% of patients treated with ACV and in 37% of patients treated with GCV + ACV (P=0.001). CMV disease developed in 23% of patients treated with ACV and in 11% of patients treated with GCV + ACV (P=0.03). In seronegative recipients of allografts from CMV-seropositive donors (D+/R-), CMV disease developed in 58% of patients treated with ACV and in 25% of patients treated with GCV + ACV (P=0.04). In the D+/R- group, 54% of patients treated with ACV and 17% of patients treated with GCV + ACV developed infection with Candida albicans (P=0.05). CONCLUSIONS: Prophylaxis of CMV infection in liver-transplant patients with 14 days of intravenous GCV followed by high-dosage oral ACV is more effective than high-dosage oral ACV alone at reducing CMV infection and disease, even for patients in the D+/R- CMV serological group.

Mitochondrial transmission during mating in Saccharomyces cerevisiae is determined by mitochondrial fusion and fission and the intramitochondrial segregation of mitochondrial DNA.

To gain insight into the process of mitochondrial transmission in yeast, we directly labeled mitochondrial proteins and mitochondrial DNA (mtDNA) and observed their fate after the fusion of two cells. To this end, mitochondrial proteins in haploid cells of opposite mating type were labeled with different fluorescent dyes and observed by fluorescence microscopy after mating of the cells. Parental mitochondrial protein markers rapidly redistributed and colocalized throughout zygotes, indicating that during mating, parental mitochondria fuse and their protein contents intermix, consistent with results previously obtained with a single parentally derived protein marker. Analysis of the three-dimensional structure and dynamics of mitochondria in living cells with wide-field fluorescence microscopy indicated that mitochondria form a single dynamic network, whose continuity is maintained by a balanced frequency of fission and fusion events. Thus, the complete mixing of mitochondrial proteins can be explained by the formation of one continuous mitochondrial compartment after mating. In marked contrast to the mixing of parental mitochondrial proteins after fusion, mtDNA (labeled with the thymidine analogue 5-bromodeoxyuridine) remained distinctly localized to one half of the zygotic cell. This observation provides a direct explanation for the genetically observed nonrandom patterns of mtDNA transmission. We propose that anchoring of mtDNA within the organelle is linked to an active segregation mechanism that ensures accurate inheritance of mtDNA along with the organelle.