A large number of mammals, including humans, have intricate outer ear shapes that diffract incoming sound in a direction-and frequency-specific manner. Through this physical process, the outer ear shapes encode sound-source information into the sensory signals from each ear. Our results show that horseshoe bats could dynamically control these diffraction processes through fast nonrigid ear deformations. The bats' ear shapes can alter between extreme configurations in about 100 ms and thereby change their acoustic properties in ways that would suit different acoustic sensing tasks.

Morphology of the nucleus is an important regulator of gene expression. Nuclear morphology is in turn a function of the forces acting on it and the mechanical properties of the nuclear envelope. Here, we present a two-parameter, nondimensional mechanical model of the nucleus that reveals a relationship among nuclear shape parameters, such as projected area, surface area, and volume. Our model fits the morphology of individual nuclei and predicts the ratio between forces and modulus in each nucleus. We analyzed the changes in nuclear morphology of liver cells due to hepatitis C virus (HCV) infection using this model. The model predicted a decrease in the elastic modulus of the nuclear envelope and an increase in the pre-tension in cortical actin as the causes for the change in nuclear morphology. These predictions were validated biomechanically by showing that liver cells expressing HCV proteins possessed enhanced cellular stiffness and reduced nuclear stiffness. Concomitantly, cells expressing HCV proteins showed downregulation of lamin-A,C and upregulation of b-actin, corroborating the predictions of the model. Our modeling assumptions are broadly applicable to adherent, monolayer cell cultures, making the model amenable to investigate changes in nuclear mechanics due to other stimuli by merely measuring nuclear morphology. Toward this, we present two techniques, graphical and numerical, to use our model for predicting physical changes in the nucleus.Huh7 and HCV replicon cells were seeded at 80% confluency in 35-mm dishes and allowed to grow for 24 h. Huh7 cells were treated with 6 mM Nondimensional Mechanical Nuclear Model

Coxsackievirus B3 is an enterovirus, with positive-sense single-stranded RNA genome containing 'Internal Ribosome Entry Site' (IRES) in the 5ʹUTR. Once sufficient viral proteins are synthesized in the cell from the input RNA, viral template switches from translation to replication to synthesize negativestrand RNA. Inhibition of translation is a key step in regulating this switch as the positive-strand RNA template should be free of ribosomes to enable polymerase movement. In this study, we show how a host protein hnRNP C1/C2 inhibits viral RNA translation. hnRNP C1/C2 interacts with stem-loop V in the IRES and displaces poly-pyrimidine tract binding protein, a positive regulator of translation. We further demonstrate that hnRNP C1/C2 induces translation to replication switch, independently from the already known role of the ternary complex (PCBP2-3CD-cloverleaf RNA). These results suggest a novel function of hnRNP C1/C2 in template switching of positive-strand from translation to replication by a new mechanism. Using mathematical modelling, we show that the differential affinity of hnRNP C1/C2 for positive and negative-strand RNAs guides the final ± RNA ratio, providing first insight in the regulation of the positive to negative-strand RNA ratio in enteroviruses.

We present a perfusion culture system with miniature bioreactors and peristaltic pumps. The bioreactors are designed for perfusion, live-cell imaging studies, easy incorporation of microfabricated scaffolds, and convenience of operation in standard cell culture techniques. By combining with miniature peristaltic pumps—one for each bioreactor to avoid cross-contamination and to maintain desired flow rate in each—we have made a culture system that facilitates perfusion culture inside standard incubators. This scalable system can support multiple parallel perfusion experiments. The major components are fabricated by three-dimensional printing using VeroWhite, which we show to be amenable to ex vivo cell culture. Furthermore, the components of the system can be reused, thus making it economical. We validate the system and illustrate its versatility by culturing primary rat hepatocytes, live imaging the growth of mouse fibroblasts (NIH 3T3) on microfabricated ring-scaffolds inserted into the bioreactor, performing perfusion culture of breast cancer cells (MCF7), and high-magnification imaging of hepatocarcinoma cells (HuH7).