Medical research: Cell division

A thought provoking discussion

In 1962, Leonard Hayflick created a cell strain from an aborted fetus. More than 50 years later, WI-38 remains a crucial, but controversial, source of cells.

The woman was four months pregnant, but she didn't want another child. In 1962, at a hospital in Sweden, she had a legal abortion.

The fetus — female, 20 centimetres long and wrapped in a sterile green cloth — was delivered to the Karolinska Institute in northwest Stockholm. There, the lungs were dissected, packed on ice and dispatched to the airport, where they were loaded onto a transatlantic flight. A few days later, Leonard Hayflick, an ambitious young microbiologist at the Wistar Institute for Anatomy and Biology in Philadelphia, Pennsylvania, unpacked that box.

Working with a pair of surgical scalpels, Hayflick minced the lungs — each about the size of an adult fingertip — then placed them in a flask with a mix of enzymes that fragmented them into individual cells. These he transferred into several flat-sided glass bottles, to which he added a nutrient broth. He laid the bottles on their sides in a 37 °C incubation room. The cells began to divide.

http://www.nature.com/news/medical-research-cell-division-1.13273

Patterning droplets with durotaxis

Robert W. Stylea,b, Yonglu Cheb, Su Ji Parkc, Byung Mook Weond, Jung Ho Jec, Callen Hylande, Guy K. Germanb, Michael P. Powerf, Larry A. Wileng, John S. Wettlaufera,h,i,j, and Eric R. Dufresneb,i,k,l,m,1

Numerous cell types have shown a remarkable ability to detect and move along gradients in stiffness of an underlying substrate—a pro- cess known as durotaxis. The mechanisms underlying durotaxis are still unresolved, but generally believed to involve active sensing and locomotion. Here, we show that simple liquid droplets also undergo durotaxis. By modulating substrate stiffness, we obtain fine control of droplet position on soft, flat substrates. Unlike other control mech- anisms, droplet durotaxis works without imposing chemical, thermal, electrical, or topographical gradients. We show that droplet durotaxis can be used to create large-scale droplet patterns and is potentially useful for many applications, such as microfluidics, thermal control, and microfabrication. 

Light-Controlled Graphene-Elastin Composite Hydrogel Actuators

Eddie Wang, Malav S. Desai, and Seung-Wuk Lee*
Department of Bioengineering, University of California, Berkeley, Berkeley, California 94720, United States
Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States 

 
ABSTRACT: Hydrogels actuators (HAs) that can reversibly respond to stimuli have applications in diverse fields. However, faster response rates and improved control over actuation timing and location are required to fulfill their potential. To address these criteria, we synthesized near-infrared light-driven HAs by interfacing genetically engineered elastin-like polypeptides with reduced-graphene oxide sheets. The resulting nanocomposites exhibited rapid and tunable motions controlled by light position, intensity, and path, including finger-like flexing and crawling. This work demonstrates the ability of rationally designed proteins to be combined with synthetic nanoparticles for the creation of macroscale functional materials.
 

 

 

Electronic Measurements of Single-Molecule Processing by DNA Polymerase I (Klenow Fragment)

Tivoli J. Olsen †, Yongki Choi §, Patrick C. Sims §, O. Tolga Gul §, Brad L. Corso §, Chengjun Dong §, William A. Brown †, Philip G. Collins *§, and Gregory A. Weiss *†
Departments of †Chemistry, §Physics and Astronomy, and Molecular Biology, University of California, Irvine, California 92697, United States
J. Am. Chem. Soc., 2013, 135 (21), pp 7855–7860
DOI: 10.1021/ja311603r
Publication Date (Web): April 30, 2013
Copyright © 2013 American Chemical Society

Bioconjugating single molecules of the Klenow fragment of DNA polymerase I into electronic nanocircuits allowed electrical recordings of enzymatic function and dynamic variability with the resolution of individual nucleotide incorporation events. Continuous recordings of DNA polymerase processing multiple homopolymeric DNA templates extended over 600 s and through >10 000 bond-forming events. An enzymatic processivity of 42 nucleotides for a template of the same length was directly observed. Statistical analysis determined key kinetic parameters for the enzyme’s open and closed conformations. Consistent with these nanocircuit-based observations, the enzyme’s closed complex forms a phosphodiester bond in a highly efficient process >99.8% of the time, with a mean duration of only 0.3 ms for all four dNTPs. The rate-limiting step for catalysis occurs during the enzyme’s open state, but with a nearly 2-fold longer duration for dATP or dTTP incorporation than for dCTP or dGTP into complementary, homopolymeric DNA templates. Taken together, the results provide a wealth of new information complementing prior work on the mechanism and dynamics of DNA polymerase I.

Effect of Lipid and Fatty Acid Composition of Phospholipid Vesicles on Long-Term Stability and Their Response to Staphylococcus aureus and Pseudomonas aeruginosa Supernatants

Serena E. Marshall †‡, Sung-Ha Hong ‡, N. T. Thet ‡, and A. Toby A. Jenkins *‡
†Centre for Sustainable Chemical Technologies, and ‡Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom
Langmuir, Article ASAP
DOI: 10.1021/la401679u
Publication Date (Web): May 13, 2013
Copyright © 2013 American Chemical Society

Phospholipid vesicles have been the focus of attention as potential vehicles for drug delivery, as they are biomimetic, easy to produce, and contain an aqueous compartment which can be used to carry hydrophilic material, such as drugs or dyes. Lipid vesicles used for this purpose present a particular challenge, as they are not especially stable and can rapidly break down and release their contents away from the target area, especially at physiological temperatures/environments. This study aims to investigate optimum methods for vesicle stabilization where the vesicles are employed as part of a system or technology that signals the presence of pathogenic bacteria via the effect of secreted cytolytic virulence factors on a sensor interface.(1) A number of approaches have been investigated and are presented here as a systematic study of the long-term (14 day) stability at 37 °C, and at various pHs. The response of vesicles, both in suspension and within hydrogels, to Staphylococcus aureus (RN 4282) and Pseudomonas aeruginosa (PAO1) whole bacteria, and supernatants from overnight cultures of both (containing secreted proteins but free of cells), was measured via a sensitive encapsulated carboxyfluorescein release assay. The results showed that lipid chain length, cholesterol concentration, and stabilization via photopolymer stable components were critical in achieving stability. Finally, dispersion of the optimum vesicle formulation in hydrogel matrixes was investigated, culminating in the in vivo demonstration of a simple prototype wound dressing.

How Far Can We Push Polymer Architectures?

PatrickJ.M.Stals,†,#YuanchaoLi,‡,#JoannaBurdynśka,§,#RenaudNicolay,̈†,⊥AlperNese,§ Anja R. A. Palmans,† E. W. Meijer,†,* Krzysztof Matyjaszewski,§,* and Sergei S. Sheiko‡,* 

 
ABSTRACT: We here report the synthesis and character- ization of a complex polymeric architecture based on a block copolymer with a cylindrical brush block and a single-chain polymeric nanoparticle block folded due to strong intramolecular hydrogen-bonds. The self-assembly of these constructs on mica surfaces was studied with atomic force microscopy, corroborating the distinct presence of block copolymer architectures.

Nucleation-Controlled Polymerization of Nanoparticles into Supramolecular Structures

Jing Wang †, Hongwei Xia §, Yanfeng Zhang ‡, Hua Lu ‡, Ranjan Kamat †, Andrey V. Dobrynin †, Jianjun Cheng ‡, and Yao Lin *†§

J. Am. Chem. Soc., Article ASAP
DOI: 10.1021/ja402757e
Publication Date (Web): May 22, 2013
Copyright © 2013 American Chemical Society

Controlled assembly of inorganic nanoparticles (NPs) into structurally defined supramolecular polymers will create nanomaterials with new collective properties. However, supramolecular polymerization of isotropic NPs remains a challenge because of the lack of anisotropic interactions in these monomers to undergo directional associations for the cooperative growth of supramolecular chains. Herein we report self-assembly behavior of poly(l-glutamic acid)-grafted gold NPs in solution and describe how combined attractive and repulsive interactions influence the shape and size of the resulting supramolecular assemblies. The study shows that the chain growth of supramolecular polymers can be achieved from the NP monomers and the process occurs in two distinct stages, with a slow nucleation step followed by a faster chain propagation step. The resulting supramolecular structures depend on both the grafting density of the poly(l-glutamic acid) on the NPs and the size of the NPs.