Flagellated bacteria swim in circles near a rigid wall.

The rotation of bacterial flagella driven by rotary motors enables the cell to swim through fluid. Bacteria run and reorient by changing the rotational direction of the motor for survival. Fluid environmental conditions also change the course of swimming; for example, cells near a solid boundary draw circular trajectories rather than straight runs. We present a bacterium model with a single flagellum that is attached to the cell body and investigate the effect of the solid wall on bacterial locomotion. The cell body of the bacterium is considered to be a rigid body and is linked via a rotary motor to the elastic flagellum which is modeled by the Kirchhoff rod theory. The hydrodynamic interaction of the cell near a solid boundary is described using the regularized Stokes formulation combined with the image system. We show that the trajectories of the bacteria near a solid boundary are influenced by the rotation rate of the motor, the shape of the cell body, helical geometry, and elastic properties of the flagellum.

Instabilities of a rotating helical rod in a viscous fluid.

Bacteria such as Vibrio alginolyticus swim through a fluid by utilizing the rotational motion of their helical flagellum driven by a rotary motor. The flagellar motor is embedded in the cell body and turns either clockwise (CW) or counterclockwise (CCW), which may lead to straight forward or backward swimming, or reorientation of the cell. In this paper we investigate the dynamics of the helical flagellum by adopting the Kirchhoff rod theory in which the flagellum is described as a space curve associated with orthonormal triads that measure the degree of bending and twisting of the rod. The hydrodynamic interaction with the flagellum is described by the regularized Stokes formulation. We focus on two different types of instabilities: (1) whirling instability of a rotating helical filament in the absence of a hook and (2) buckling instability of a flagellum in the presence of a compliant hook that links the flagellar filament to the rotary motor. Our simulation results show that the helical filament without a hook displays three regimes of dynamical motions: stable twirling, unstable whirling, and stable overwhirling motions depending on the physical parameters, such as rotational frequency and elastic properties of the flagellum. The helical filament with a hook experiences buckling instability when the motor switches the direction of rotation and the elastic properties of the hook change. Variations of physical parameter values of the hook such as the bending modulus and the length make an impact on the buckling angle, which may subsequently affect the reorientation of the cell.

National trends for open and endovascular repair of aneurysms in Korea: 2004-2013.

The introduction of endovascular aneurysm repair has led to a dramatic decline in open aneurysm repair. The aim of this report was to evaluate Korean national trends for the treatment of aneurysms. A serial, cross-sectional study of time trends of patients who underwent aneurysm repair between 2004 and 2013 was conducted. Data from the Health Insurance Review and Assessment Service were used to evaluate the trends of aneurysm repair in the Korean population and to analyze the trends of open and endovascular aneurysm repair among Medicare beneficiaries. A linear-by-linear association was performed to determine alterations in the rates at which these aneurysm repair techniques were performed. A total of 32,130 patients underwent aneurysm repair between 2004 and 2013. The proportion of patients who underwent open repair decreased from 94.0% in 2004 to 54.9% in 2013; whereas the proportion of patients who underwent endovascular repair increased from 6.0% in 2004 to 45.1% in 2013. During the study period, the number of patients undergoing endovascular repair of aortic aneurysms significantly increased from 82 to 1,396 (relative risk, 16.17; 95% confidence interval: 12.94-20.21). Endovascular repair of abdominal aortic aneurysms (AAAs)overtook open repair between 2010 and 2011. The frequency of open aneurysm repair increased 1.2-fold, with an overall downward trend. The prevalence of endovascular repair markedly increased 15.3-fold. These findings indicated that, in Korea, the endovascular repair of AAAs overtook open repair as the most common technique between 2010 and 2011.

In silico analysis of genomic data for construction of nuclear receptor network.

Availability of genome-wide information in public database provides unprecedented opportunity for developing new strategy to uncover potential interactions of members in large functional family. Here we describe a systematic strategy for constructing and analyzing potential interaction map to uncover novel interaction between nuclear receptors that may play important roles in human disease. This in silico approach can prioritize candidate interactions for further functional validation and assess its clinical relevance.

The atypical orphan nuclear receptor DAX-1 interacts with orphan nuclear receptor Nur77 and represses its transactivation.

DAX-1 (dosage-sensitive sex reversal adrenal hypoplasia congenital critical region on the X chromosome, gene 1) (NROB1) is an atypical member of the nuclear receptor family, which lacks the classical zinc finger DNA binding domain and acts as a coregulator of a number of nuclear receptors. In this study, we have found that DAX-1 is a novel coregulator of the orphan nuclear receptor Nur77 (NR4A1). We demonstrate that DAX-1 represses the Nur77 transactivation by transient transfection assays. Specific interaction between Nur77 and DAX-1 was detected by coimmunoprecipitation, yeast two-hybrid, and glutathione-S-transferase pull-down assays. The ligand binding domain of DAX-1 and the activation function-2 domain of Nur77 were determined as the direct interaction domains between DAX-1 and Nur77. In vitro competition binding assay showed that DAX-1 repressed Nur77 transactivation through the competition with steroid receptor coactivator-1 for the binding of Nur77. Moreover, DAX-1 repressed Nur77- and LH-dependent increase of cytochrome P450 protein 17 promoter activity in transient transfection assays. Furthermore, Nur77-mediated transactivation was significantly increased by down-regulation of DAX-1 expression with DAX-1 small interfering RNA in testicular Leydig cell line, K28. LH treatment induced a transient increase in Nur77 mRNA, whereas LH repressed DAX-1 expression in a time- and dose-dependent manner in K28 cells. In addition, immunohistochemical analysis showed the expression of Nur77 in mouse testicular Leydig cells. These results suggest that DAX-1 acts as a novel coregulator of the orphan nuclear receptor Nur77, and that the DAX-1 may play a key role in the regulation of Nur77-mediated steroidogenesis in testicular Leydig cells.