Popular science articles: March 2013

Flies can be distinguished by their wing Spots

Some flies in the Drosophila melanogaster lineage exhibit wing spots, which vary among species. Examining the underlying genetics of spot determination, Arnoult et al. (p.1423) provide evidence for a two-step scenario for the origin and diversification of patterning novelty in these fly wings. The findings suggest that the two-step model may generally apply to the emergence and diversification of traits in plants and animals.

Bilayer Thickness Mismatch Controls Domain Size in Model Membranes

Frederick A. Heberle *†, Robin S. Petruzielo §,Jianjun Pan †, Paul Drazba

, Norbert Kučerka

□,Robert F. Standaert †‡#, Gerald W. Feigenson

, and John Katsaras *†

◊

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja3113615

Publication Date (Web): February 7, 2013

The observation of lateral phase separation in lipid bilayers has received considerable attention, especially in connection to lipid raft phenomena in cells. It is widely accepted that rafts play a central role in cellular processes, notably signal transduction. While micrometer-sized domains are observed with some model membrane mixtures, rafts much smaller than 100 nm—beyond the reach of optical microscopy—are now thought to exist, both in vitro and in vivo. We have used small-angle neutron scattering, a probe free technique, to measure the size of nanoscopic membrane domains in unilamellar vesicles with unprecedented accuracy. These experiments were performed using a four-component model system containing fixed proportions of cholesterol and the saturated phospholipid 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC), mixed with varying amounts of the unsaturated phospholipids 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). We find that liquid domain size increases with the extent of acyl chain unsaturation (DOPC:POPC ratio). Furthermore, we find a direct correlation between domain size and the mismatch in bilayer thickness of the coexisting liquid-ordered and liquid-disordered phases, suggesting a dominant role for line tension in controlling domain size. While this result is expected from line tension theories, we provide the first experimental verification in free-floating bilayers. Importantly, we also find that changes in bilayer thickness, which accompany changes in the degree of lipid chain unsaturation, are entirely confined to the disordered phase. Together, these results suggest how the size of functional domains in homeothermic cells may be regulated through changes in lipid composition.

Reversible Assembly of Stacked Membrane Nanodiscs with Reduced Dimensionality and Variable Periodicity

Paul A. Beales *†, Nienke Geerts ‡, Krishna K. Inampudi ‡, Hideki Shigematsu

, Corey J. Wilson‡, and T. Kyle Vanderlick *‡

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja311561d

Publication Date (Web): February 13, 2013

We demonstrate the self-organization of quasi-one-dimensional nanostructures with periodic features using nature’s primary three building blocks: lipids, DNA, and proteins. The periodicity of these “BioNanoStacks” is controllable through selection of the length of the DNA spacers. We show that BioNanoStacks can be reversibly assembled and disassembled through thermal melting of the DNA duplex, where the melting transition temperature is controllable not just by the DNA sequence and salt concentration, but also by the lipid composition within these superstructures. These novel materials may find applications in fields such as templated nanomaterial assembly, tissue-engineering scaffolds, or therapeutic delivery systems. Well-established techniques for chemical modification of biomolecules will also provide a broad platform for adaption and remodeling of these structures to provide optimal features for the required application.

Multifunctional, Ultra-Flyweight, Synergistically Assembled Carbon Aerogels

Haiyan Sun,
Zhen Xu,
Chao Gao^*

^{Article first published online: 18 FEB 2013

DOI: 10.1002/adma.201204576

All carbon aerogels (up to 1000 cm³) with ultralow density (down to 0.16 mg cm⁻³) and temperature-invariant (-190–900 °C) super-elasticity are fabricated by facile assembling of commercial carbon nanotubes (CNTs) and chemically-converted giant graphene sheets, on the basis of the synergistic effect between elastic CNTs ribs and giant graphene cell walls.}

Multifunctional Epidermal Electronics Printed Directly Onto the Skin

Woon-Hong Yeo , Yun-Soung Kim , Jongwoo Lee , Abid Ameen , Luke Shi , Ming Li ,
Shuodao Wang , Rui Ma , Sung Hun Jin , Zhan Kang , Yonggang Huang ,
and John A. Rogers *

Materials and designs are presented for electronics and sensors that can be conformally and robustly integrated onto the surface of the skin. A multifunctional device of this type can record various physiological signals relevant to health and wellness. This class of technology offers capabilities in biocompatible, non-invasive measurement that lie beyond those available with conventional, point-contact electrode interfaces to the skin.

Conclusions Regarding Cross-Group Differences in Happiness Depend on Difficulty of Reaching Respondents

Ori Heffetz

Cornell University - S.C. Johnson Graduate School of Management

Matthew Rabin

University of California, Berkeley - Department of Economics
January 25, 2013

American Economic Review, Forthcoming
Abstract:
A growing literature explores differences in subjective well-being across demographic groups, often relying on surveys with high nonresponse rates. By using the reported number of call attempts made to participants in the University of Michigan’s Surveys of Consumers, we show that comparisons among easy-to-reach respondents differ from comparisons among hard-to-reach ones. Notably, easy-to-reach women are happier than easy-to-reach men, but hard-to-reach men are happier than hard-to-reach women, and conclusions of a survey could reverse with more attempted calls. Better alternatives to comparing group sample averages might include putting greater weight on hard-to-reach respondents or even extrapolating trends in responses.