Internal Motility in Stiffening Actin-Myosin Networks

We present a study on filamentous actin solutions containing heavy meromyosin subfragments of myosin II motor molecules. We focus on the viscoelastic phase behavior and internal dynamics of such networks during ATP depletion. Upon simultaneously using micro-rheology and fluorescence microscopy as complementary experimental tools, we find a sol-gel transition accompanied by a sudden onset of directed filament motion. We interpret the sol-gel transition in terms of myosin II enzymology, and suggest a "zipping" mechanism to explain the filament motion in the vicinity of the sol-gel transition.Comment: 4 pages, 3 figure

Ambiguity in a Real Option Game

In this paper we study a two-player investment game with a first mover advantage in continuous time with stochastic payoffs, driven by a geometric Brownian motion. One of the players is assumed to be ambiguous with maxmin preferences over a strongly rectangular set of priors. We develop a strategy and equilibrium concept allowing for ambiguity and show that equilibira can be preemptive (a player invests at a point where investment is Pareto dominated by waiting) or sequential (one player invests as if she were the exogenously appointed leader). Following the standard literature, the worst case prior for the ambiguous player if she is the second mover is obtained by setting the lowest possible trend in the set of priors. However, if the ambiguous player is the first mover, then the worst case prior can be given by either the lowest or the highest trend in the set of priors. This novel result shows that "worst case prior" in a setting with geometric Brownian motion and kappa-ambiguity does not equate to "lowest trend"

Rivalry and uncertainty in complementary investments with dynamic market sharing

We study the effects of revenue and investment cost uncertainty, as well non- preemption duopoly competition, on the timing of investments in two complementary inputs, where either spillover-knowledge is allowed or proprietary-knowledge holds. We find that the ex-ante and ex-post revenue market shares play a very important role in firms’ behavior. When competition is considered, the leader’s behavior departs from that of the monopolist firm of Smith (Ind Corp Change 14:639–650, 2005). The leader is justified in following the conventional wisdom (i.e., synchronous investments are more likely), whereas, the follower’s behavior departs from that of the conventional wisdom (i.e., asynchronous investments are more likely)

Immunological Responses and Actin Dynamics in Macrophages Are Controlled by N-Cofilin but Are Independent from ADF

Dynamic changes in the actin cytoskeleton are essential for immune cell function and a number of immune deficiencies have been linked to mutations, which disturb the actin cytoskeleton. In macrophages and dendritic cells, actin remodelling is critical for motility, phagocytosis and antigen presentation, however the actin binding proteins, which control antigen presentation have been poorly characterized. Here we dissect the specific roles of the family of ADF/cofilin F-actin depolymerizing factors in macrophages and in local immune responses

Relationship among fibre type, myosin ATPase activity and contractile properties

At least two types of skeletal muscle myosin have been described which differ in ATPase activity and stability in alkaline or acidic media. Differences in ATPase characteristics distinguish Type I and Type II fibres histochemically. In this study, ATPase activity of myosin from muscles of several species with known histochemical and contractile properties has been determined to test the hypothesis that (1) myosin ATPase activity, (2) histochemical determination of fibre types and (3) maximum shortening velocity, all provide equivalent estimates of contractile properties in muscles of mixed fibre types. Maximum shortening velocity appears to be proportional to ATPase activity as expected from previous reports by Barany. However, both myosin ATPase and the maximum shortening velocity exhibit curvilinear relationships to the fraction of cross-sectional area occupied by Type II fibres. Therefore, we reject the hypothesis and conclude that histochemically determined myofibrillar ATPase does not accurately reflect the intrinsic ATPase activity or shortening velocity in muscles of mixed fibre types. Our data are consistent with the presence of more than two myosin isozymes or with a mixture of isozymes within single muscle fibres.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42851/1/10735_2005_Article_BF01005238.pd