Contraction Mechanisms in Composite Active Actin Networks

Simplified in vitro systems are ideally suited for studying the principle mechanisms of the contraction of cytoskeletal actin systems. To shed light on the dependence of the contraction mechanism on the nature of the crosslinking proteins, we study reconstituted in vitro active actin networks on different length scales ranging from the molecular organization to the macroscopic contraction. Distinct contraction mechanisms are observed in polar and apolar crosslinked active gels whereas composite active gels crosslinked in a polar and apolar fashion at the same time exhibit both mechanisms simultaneously. In polar active actin/fascin networks initially bundles are formed which are then rearranged. In contrast, apolar cortexillin-I crosslinked active gels are bundled only after reorganization of actin filaments by myosin-II motor filaments

Modern radiation therapy and potential fertility preservation strategies in patients with cervical cancer undergoing chemoradiation

Young patients with cervical cancer who undergo chemoradiation might be interested in fertility preservation, not only dependent upon the use of a gestational carrier as maybe achieved by the use of ovarian transposition and cryo-conservation of oocytes or ovarian tissue, but may prefer to carry pregnancy to term after cancer treatment. The latter approach is a non- established concept needing both modern radiation therapy approaches as well as modifications -if at all possible- in current recommendations for target volume delineation to spare dose to the unaffected uterus. Future strategies to serve selected patients in this respect should only be conducted in prospective clinical evaluations and are critically discussed in this article

Rectum separation in patients with cervical cancer for treatment planning in primary chemo-radiation

PURPOSE: To proof feasibility of hydrogel application in patients with advanced cervical cancer undergoing chemo-radiation in order to reduce rectal toxicity from external beam radiation as well as brachytherapy. MATERIAL AND METHODS: Under transrectal sonographic guidance five patients with proven cervical cancer underwent hydro gel (20 cc) instillation into the tip of rectovaginal septum adherent to posterior part of the visible cervical tumor. Five days after this procedure all patients underwent T2 weighted transversal and sagittal MRI for brachytherapy planning. MRI protocol included T2 weighted fast spin echo (FSE) imaging in sagittal, coronal and para-axial orientation using an 1.5 Tesla MRI. Separation of anterior rectal wall and cervix was documented. RESULTS: Hydrogel application was uneventful in all patients and no toxicity was reported. Separation ranged from 7 to 26 mm in width (median 10 mm). The length of the separation varied between 18 and 38 mm (median 32 mm). In all patients displacement was seen in the posterior vaginal fornix, and/or at the deepest part of uterine cervix depending on the extension of the cul-de-sac in correlation to the posterior wall of the uterus. In patients with bulky tumor and/or deep (vaginal) extend of peritoneal cavity tumour was seen mainly cranial from the rectovaginal space and therefore above the hydrogeI application. Only in the extra-peritoneal (lower) part of the cervix a good separation could be achieved between the rectum and cervix. CONCLUSION: Hydrgel instillation in patients with cervial cancer undergoing chemoradiation is safe and feasible. Because of the loose tissue of the cul-de-sac and its intra- and extraperitoneal part, hydrogel instillation of 20 cc did not result in a sufficient separation of the cervix from anterior wall

UTILIZAÇÃO DO PARASITOIDE Habrobracon hebetor (HYMENOPTERA: BRACONIDAE) COMO ESTRATÉGIA DE MANEJO NA PÓS-COLHEITA

A implantação de políticas públicas que visam diminuir o uso de agrotóxicos e a valorização de alimentos produzidos sem a aplicação dos mesmos, tem levado pesquisadores e agricultores a buscarem formas alternativas para o manejo de pragas agrícolas. Dentre as técnicas, o controle biológico é uma ferramenta de manejo que utiliza meios naturais para diminuir populações de organismos que são considerados pragas, sem haver a necessidade de utilizar agrotóxicos. Entre os insetos que são utilizados como agentes de controle biológico, estão os parasitoides. Na pós-colheita, o ectoparasitoide Habrobracon hebetor (Say, 1857) (Hymenoptera: Braconidae) se destaca como um promissor agente controlador de traças, as quais acometem uma infinidade de produtos, como farinha, milho, tabaco, cacau, cereais e seus derivados. Quando liberados nos galpões/armazéns, as fêmeas do parasitoide localizam as larvas dos seus hospedeiros que estão consumindo o produto e depositam seus ovos sobre estas, interrompendo o desenvolvimento da praga. Portanto, com a liberação de forma aumentativa desse parasitoide ocorre a supressão no desenvolvimento da praga reduzindo a sua população e evitando assim, danos econômicos ao produtor. No entanto, fatores como fotoperíodo, temperatura, hospedeiro de origem e dieta de criação, podem afetar os processos de interação entre parasitoide e hospedeiro, interferindo no controle biológico em ambientes de armazenamento.

Efeito do fotoperíodo sobre parâmetros de esperança de vida e fertilidade de Habrobracon hebetor (Hymenoptera, Braconidae) em larvas de Ephestia kuehniella (Lepidoptera, Pyralidae)

Fatores abióticos como fotoperíodo podem afetar os processos de interação entre o ectoparasitoide Habrobracon hebetor e seu hospedeiro Ephestia kuehniella. Sendo assim, objetivou-se avaliar o desenvolvimento e os parâmetros de esperança de vida e de fertilidade de H. hebetor, parasitando E. kuehniella sob diferentes fotoperíodos. Os parasitoides desenvolveram-se durante a fase pré-imaginal em três diferentes fotoperíodos (claro/escuro) 24:0, 12:12 e 0:24, e os adultos oriundos de cada um dos tratamentos ficaram expostos a 0, 12 e 24 horas de fotofase, perfazendo nove tratamentos. Um casal de parasitoides foi inserido por placa de Petri contendo 10 larvas de quinto instar de E. kuehniella, e a cada 24 horas eram retirados e transferidos para uma nova placa com 10 larvas, até a morte da fêmea. A duração do período pré-imaginal em escotofase foi significativamente maior que os períodos com fotofases de 12 e 24 horas. A longevidade das fêmeas e dos machos não diferiu entre os tratamentos. A esperança de vida das fêmeas variou de 7,7 a 10,2 dias. As taxas líquidas de reprodução dos parasitoides criados em fotofase de 12 e 24 horas foram em média de 52,7 a 63,7, maiores que em escotofase (22,9 a 27,9)

Constructive approach to limiting periodic orbits with exponential and power law dynamics

In dynamical systems limit cycles arise as a result of a Hopf bifurcation, after a control parameter has crossed its critical value. In this study we present a constructive method to produce dissipative dynamics which lead to stable periodic orbits as time grows, with predesigned transient dynamics. Depending on the construction method a) the limiting orbit can be a regular circle, an ellipse or a more complex closed orbit and b) the approach to the limiting orbit can follow an exponential law or a power law. This technique allows to design nonlinear models of dynamical systems with desired (exponential or power law) relaxation properties.Comment: 17 pages, 6 figure

Structure formation in active networks

Structure formation and constant reorganization of the actin cytoskeleton are key requirements for the function of living cells. Here we show that a minimal reconstituted system consisting of actin filaments, crosslinking molecules and molecular-motor filaments exhibits a generic mechanism of structure formation, characterized by a broad distribution of cluster sizes. We demonstrate that the growth of the structures depends on the intricate balance between crosslinker-induced stabilization and simultaneous destabilization by molecular motors, a mechanism analogous to nucleation and growth in passive systems. We also show that the intricate interplay between force generation, coarsening and connectivity is responsible for the highly dynamic process of structure formation in this heterogeneous active gel, and that these competing mechanisms result in anomalous transport, reminiscent of intracellular dynamics