28 research outputs found
Patterns of the Ferrocyanide-Iodate-Sulfite Reaction Revisited: The Role of Immobilized Carboxylic Functions
4 pagesInternational audienceWe experimentally demonstrate that the standing lamella reaction-diffusion patterns initially observed 17 years ago in a gel-filled open spatial reactor operated with the ferrocyanide-iodate-sulfite bistable reaction requires an upper critical concentration of low-mobility species with weak acid functional groups, a parameter that was overlooked at the time and had made observations difficult to reproduce. The present approach enables the control of the space scale separation between activatory and inhibitory processes. It makes the wealth of exotic pattern dynamics observed earlier easier to reproduce and understand. This contribution should considerably revive the interest in this reaction and boost the search for the control of reaction-diffusion patterns in other bistable systems.Wave and pattern--
A New Antigen Recognized by Cytolytic T Lymphocytes on a Human Kidney Tumor Results from Reverse Strand Transcription
By stimulating blood lymphocytes from a renal cell carcinoma patient in vitro with the autologous tumor cells, we obtained cytolytic T lymphocyte (CTL) clones that killed several autologous and allogeneic histocompatibility leukocyte antigen (HLA)-B7 renal carcinoma cell lines. We identified the target antigen of these CTLs by screening COS cells transfected with the HLA-B7 cDNA and with a cDNA library prepared with RNA from the tumor cells. The antigenic peptide recognized by the CTLs has the sequence LPRWPPPQL and is encoded by a new gene, which we named RU2. This gene is transcribed in both directions. The antigenic peptide is not encoded by the sense transcript, RU2S, which is expressed ubiquitously. It is encoded by an antisense transcript, RU2AS, which starts from a cryptic promoter located on the reverse strand of the first intron and ends up on the reverse strand of the RU2S promoter, which contains a polyadenylation signal. This mechanism of antigen expression is unprecedented and further illustrates the notion that many peptides recognized by T cells cannot be predicted from the primary structure of the major product of the encoding gene. Antisense transcript RU2AS is expressed in a high proportion of tumors of various histological types. It is absent in most normal tissues, but is expressed in testis and kidney, and, at lower levels, in urinary bladder and liver. Short-term cultures of normal epithelial cells from the renal proximal tubule expressed significant levels of RU2AS message and were recognized by the CTLs. Therefore, this antigen is not tumor specific, but corresponds to a self-antigen with restricted tissue distribution
Structures de non-équilibre et bistabilité spatiale dans des systèmes de réaction-diffusion
BORDEAUX1-BU Sciences-Talence (335222101) / SudocSudocFranceF
Pattern formation in the ferrocyanide-iodate-sulfite reaction: The control of space scale separation
We revisit the conditions for the development of reaction-diffusion patterns in the ferrocyanide-iodate-sulfite bistable and oscillatory reaction. This hydrogen ion autoactivated reaction is the only example known to produce sustained stationary lamellar patterns and a wealth of other spatio-temporal phenomena including self-replication and localized oscillatory domain of spots, due to repulsive front interactions and to a parity-breaking front bifurcation (nonequilibrium Ising-Bloch bifurcation). We show experimentally that the space scale separation necessary for the observation of stationary patterns is mediated by the presence of low mobility weak acid functional groups. The presence of such groups was overlooked in the original observations made with hydrolyzable polyacrylamide gels. This missing information made the original observations difficult to reproduce and frustrated further experimental exploitation of the fantastic potentialities of this system. Using one-side-fed spatial reactors filled with agarose gel, we can reproduce all the previous pattern observations, in particular the stationary labyrinthine patterns, by introducing, above a critical concentration, well controlled amounts of polyacrylate chains in the gel network. We use two different geometries of spatial reactors (annular and disk shapes) to provide complementary information on the actual three-dimensional character of spatial patterns. We also reinvestigate the role of other feed parameters and show that the system exhibits both a domain of spatial bistability and of large-amplitude pH oscillations associated in a typical cross-shape diagram. The experimental method presented here can be adapted to produce patterns in the large number of oscillatory and bistable reactions, since the iodate-sulfite-ferrocynide reaction is a prototype of these systems
Patterns of the Ferrocyanide-Iodate-Sulfite Reaction Revisited: The Role of Immobilized Carboxylic Functions
We experimentally demonstrate that the standing lamella reaction-diffusion patterns initially observed 17 years ago in a gel-filled open spatial reactor operated with the ferrocyanide-iodate-sulfite bistable reaction requires an upper critical concentration of low-mobility species with weak acid functional groups, a parameter that was overlooked at the time and had made observations difficult to reproduce. The present approach enables the control of the space scale separation between activatory and inhibitory processes. It makes the wealth of exotic pattern dynamics observed earlier easier to reproduce and understand. This contribution should considerably revive the interest in this reaction and boost the search for the control of reaction-diffusion patterns in other bistable systems.Wave and pattern--
AN EFFECTIVE DESIGN METHOD TO PRODUCE STATIONARY CHEMICAL REACTION-DIFFUSION PATTERNS
We present a semi-empirical experimental design method to produce nontrivial chemical reaction-di usion patterns in open reactors. We specially focus on the development of stationary patterns. The method is based on autoactivated reactions that produces spatial bistability, the addition of an independent antagonist reaction to produce spatio-temporal oscillations, and the introduction of a low mobility complexing agent that rapidly and reversibly binds the main autoactivatory species. The method is presented in formal way. Actual experimental results are used for illustration. We point out the open problems of the mathematical description: they relate to the boundary conditions, to the dimensionality of the system, and to the coupled time- and space-scale changes induced by the complexing agent
Turing Patterns and Waves in Closed Two-Layer Gel Reactors
Reaction–diffusion
waves and stationary Turing patterns
are observed in closed two-layer gel reactors, where the two compartments
are initially filled with complementary sets of reactants of the chlorine
dioxide–iodine–malonic acid–poly(vinyl alcohol)
reaction. The asymmetrical loading generates concentration gradients
and the patterns form at the interface between the two parts. These
easy-to-perform experiments allow us to study a wide range of dynamical
phenomena without requiring a specific reactor design or the use of
sophisticated equipment. To get complementary information on pattern
formation in parallel and perpendicular to the direction of the concentration
gradients, two geometrically different configurations of compartments
are presented. We demonstrate that three variants of the initial distribution
of the chemicals can be equally applied, and this flexibility provides
a way to introduce additional reagents to perturb the dynamics of
the systems. A noticeable increase in the wavelength of Turing patterns
and in the period of waves has been induced by adding bromide ions.
The interaction of Turing and Hopf modes has been observed as a result
of not only the variation of the initial poly(vinyl alcohol) concentration
but that of the gradients as well
An Experimental Design Method Leading to Chemical Turing Patterns
Chemical reaction-diffusion patterns often serve as prototypes for pattern formation in living systems, but only two isothermal single-phase reaction systems have produced sustained stationary reaction-diffusion patterns so far. We designed an experimental method to search for additional systems on the basis of three steps: (i) generate spatial bistability by operating autoactivated reactions in open spatial reactors; (ii) use an independent negative-feedback species to produce spatiotemporal oscillations; and (iii) induce a space-scale separation of the activatory and inhibitory processes with a low-mobility complexing agent. We successfully applied this method to a hydrogen-ion autoactivated reaction, the thiourea-iodate-sulfite (TuIS) reaction, and noticeably produced stationary hexagonal arrays of spots and parallel stripes of pH patterns attributed to a Turing bifurcation. This method could be extended to biochemical reactions