The composite of the actin cytoskeleton and plasma membrane plays important roles in many biological events. Here, we employed the emulsion method to synthesize artificial cells with biomimetic actin cortex in vesicles and characterized their mechanical properties. We demonstrated that the emulsion method provides the flexibiligy to adjust the lipid composition and protein concentrations in artificial cells to achieve the desired size distribution, internal microstructure and mechanical properties. Moreover, comparison of the cortical elasticity measured for reconstituted artificial cells to that of real cells, including those manipulated useing genetic depletion and pharmacological inhibition, strongly supports that actin cytoskeletal proteins are dominant over lipid molecules in cortical mechanics. Our study indicates that the assembly of biological systems in artificial cells with purified cellular components provides a powerful way to anwer biological quesitions.

Our new results have been published in Applied Physics Letters 104, 153701 (2014). We hope that this piece of work will inspire more effort in biomimetic studies.

http://dx.doi.org/10.1063/1.4871861

or

scitation.aip.org/content/aip/journal/apl/104/15/10.1063/1.4871861

Mechanical forces direct a host of cellular and tissue processes. Although much emphasis has been places on cell-adhesion complexes as force sensors, the forces must nevertheless be transmitted through the cortical cytoskeleton. Yet how the actin cortex senses and transmits forces and how cytoskeletal proteins interact in response to the forces is poorly understood. Here, by combining molecular and mechanical experimental perturbations with theoretical multiscale modeling, we decipher cortical mechanosensing from molecular to cellular scales. We show that forces are shared between myosin II and different actin crosslinkers, with myosin having potentiating or inhibitory effects on certain crosslinkers. Different types of cell deformation elicit distinct responses, with myosin and α-actinin responding to dilation, and filamin mainly reacting to shear. Our observations show that the accumulation kinetics of each protein may be explained by its molecular mechanisms, and the protein accumulation and the cell's viscoelastic state can explain cell contraction against mechanical load.

This paper is available at Nature Materials website: www.nature.com/nmat/journal/v12/n11/full/nmat3772.html

There are six distinguished biophysicist in cell mechanics field (their research interests cover much broader areas) and the abbreviations of their first names are either C or D. They are Dr. David Weitz (Harvard U.), Dr. Christopher Chen (U. Penn.), Dr. Dennis Discher (U. Penn.), Dr. Denis Wirtz (JHU), Dr. Douglas Robinson (JHU), and Dr. Daniel Fletcher (U.C. Berkeley). These six scientists use both experimental and theoretical approaches to investigate the biological responses of proteins and cells to mechanical stimuli, such as forces and geometrical constraints. Their research extends from molecular scale to cellular level to tissue level.

Dr. David Weitz made significant contributions to the understanding of mechanical properties of biopolymers, such actin, microtubule, and intermediate filaments. His group performed most of the measurements of the microrheology of actin gel in last two decays. He invented the technique of combining the emulsion method and microfluidic device to synthesize vesicles being used for drug delivery as well as the reconstitution of artificial cells.

Dr. Christopher Chen is mostly known for his innovation of measuring the cell-substrate interaction using micropillars fabricated by soft lithography. He has also made many contributions to nanobiotechnology over the years.

Dr. Dennis Discher is famous for his outstanding contributions to the studies of cell responses (for example, change of gene expression and stem cell differentiation) to substrates with different rigidity. Meanwhile, he is known for his deep understanding of cell mechanics and polymer physics.

Dr. Denis Wirtz made important discovery about how cells sense 3D environment. He has also been active in the fields of cell mechanics, single molecule mechanics, cell division, and microrheology of biopolymer gel.

Dr. Douglas Robinson's research mainly focuses on the dynamics of cell shape changes, especially during cell division. He is known for his work on actin cytoskeleton proteins (for example, the mechanosensitivity of non-muscle myosin II).

Dr. Daniel Fletcher investigates cell motility and the remodeling of actin cytoskeleton. He is famous for using AFM to study the properties of actin network.

These six scientists are the most active leaders in cell mechanics field. Although there are other very productive scientists in this field, their research is either lack of the combination of experimental and theoretical/computational approaches or more limited to just cell level (not multiscaled).

Myosin II is a central mechanoenzyme in a wide range of cellular morphogenic processes. Its cellular localization is dependent not only on signal transduction pathways, but also on mechanical stress. We suggest that this stress-dependent distribution is the result of both the force-dependent binding to actin filaments and cooperativie interactions between bound myosin heads. By assuming that the binding of myosin heads induces and/or stabilizes local conformational changes in the actin filaments which enhances myosin II binding locally, we successfullly simulate the cooperative binding of myosin to actin observed experimentally. In addition, we can interpret the cooperative interactions between myosin and actin-crosslinking protein observed in cellular mechanosensation, provided that a similar mechanism operates among different proteins. Finally, we present a model that couples cooperative interactions to the assembly dynamics of myosin bipolar thick filaments and that accounts for the transient behaviors of the myosin II accumulation during mechanosensation. This mechanism is likely to be general for a range of myosin II-dependent cellular mechanosensory processes.

The attachement includes the manuscript and 3 gif files obstained from simulations (use "windows picture and fax viewer" or other gif players to view the gif files).

The annual International Dictyostelium Conference will be held in Baltimore, MD USA from August 14 to 18. Dictyostelium has been extensively used as a model organism for the study of cell mechanics, motility, chemotaxis, cell division and other biological events that involve cell shape change and the mechanical behaviors of cells. In this coming meeting, there will be 70 oral presentations and 100 posters covering above topics.

http://dicty11.dictybase.org

We wrote a book chapter about the role of the actin cytoskeleton in mechanosensation. The book title is Mechanosensitivity and Mechanotransduction, edited by A, Kamkin and I. Kiseleva and published by Springer-Verlag, New York.".

In this chapter, we try to integrate mechanics, materials science, biophysics and biology together to give a most updated view of this field. We also want to introduce the feedback loop concept to mechanicians who are interested in studying biological systems.

I attached the pdf version and the follwoing is the subtitles of the chapter.

Chapter 1 The Role of the Actin Cytoskeleton in Mechanosensation

Tianzhi Luo and Douglas N. Robinson

1.1. Introduction

1.2. Microstructures and deformations of the actin cytoskeleton
1.2.1 Intermolecular and intramolecular deformations
1.2.1.1 Force generation associated with actin polymerization
1.2.1.2 Force-dependent behaviors of actin-myosin binding
1.2.1.3 Force-dependent binding between actin crosslinkers and actin filaments
1.2.1.4 Force-dependent intramolecular deformation of ACLPs
1.2.2 Mechanical properties of an actin network
1.2.2.1 Mechanical properties of pure actin gels
1.2.2.2 Effects of crosslinking proteins on the microstructures and mechanical properties of pure actin networks
1.2.2.3 Effects of myosin II on the mechanical properties of the actin network
1.2.3 In vivo measurements of cell mechanics
1.3. Functions of the actin cytoskeleton in mechanosensation
1.3.1 Mechanosensing through myosin II and actin crosslinking proteins
1.3.1.1 How force might modulate myosin II bipolar thick filament assembly
1.3.1.2 Cooperativity between myosin II and cortexillin
1.3.2 Mechanosensation through focal adhesion complexes
1.3.3 The actin cytoskeleton works as a force-transmission highway
1.4. Remodeling of the actin cytoskeleton during mechanosensation
1.4.1 How mechanically activated kinases regulate the actin cytoskeleton
1.4.2 Crosstalk between microtubules and actin cytoskeleton
1.5. Experimental techniques for measuring mechanosensation-- in vitro and in vivo methods
1.6. Conclusion and perspectives

Please visit www.jove.com

You'll find tons of video about biological experiments you might be interested in. It is very useful for most of mechanicians who lack this kind of knowledge and experience. Enjoy yourself!