RESUMO
We have recorded the swarming-like collective migration of a large number of keratocytes (tissue cells obtained from the scales of goldfish) using long-term videomicroscopy. By increasing the overall density of the migrating cells, we have been able to demonstrate experimentally a kinetic phase transition from a disordered into an ordered state. Near the critical density a complex picture emerges with interacting clusters of cells moving in groups. Motivated by these experiments we have constructed a flocking model that exhibits a continuous transition to the ordered phase, while assuming only short-range interactions and no explicit information about the knowledge of the directions of motion of neighbors. Placing cells in microfabricated arenas we found spectacular whirling behavior which we could also reproduce in simulations.
Assuntos
Agregação Celular/fisiologia , Comunicação Celular/fisiologia , Carpa Dourada/fisiologia , Queratinócitos/citologia , Queratinócitos/fisiologia , Modelos Biológicos , Animais , Células Cultivadas , Simulação por Computador , Transição de FaseRESUMO
A novel assay based on micropatterning and time-lapse microscopy has been developed for the study of nuclear migration dynamics in cultured mammalian cells. When cultured on 10-20-microm wide adhesive stripes, the motility of C6 glioma and primary mouse fibroblast cells is diminished. Nevertheless, nuclei perform an unexpected auto-reverse motion: when a migrating nucleus approaches the leading edge, it decelerates, changes the direction of motion, and accelerates to move toward the other end of the elongated cell. During this process, cells show signs of polarization closely following the direction of nuclear movement. The observed nuclear movement requires a functioning microtubular system, as revealed by experiments disrupting the main cytoskeletal components with specific drugs. On the basis of our results, we argue that auto-reverse nuclear migration is due to forces determined by the interplay of microtubule dynamics and the changing position of the microtubule organizing center as the nucleus reaches the leading edge. Our assay recapitulates specific features of nuclear migration (cell polarization, oscillatory nuclear movement), while it allows the systematic study of a large number of individual cells. In particular, our experiments yielded the first direct evidence of reversive nuclear motion in mammalian cells, induced by attachment constraints.
Assuntos
Núcleo Celular/fisiologia , Proteínas do Citoesqueleto/fisiologia , Células 3T3 , Animais , Camundongos , Microscopia de Contraste de Fase , Microtúbulos/fisiologia , Fatores de TempoRESUMO
Radon exposure was shown to be carcinogenic and suggested as a possible causative factor for lung cancer in man. A hypothesis is introduced that medium high radon (between 110 and 165 Bq/m3) causes lower cancer risk among women younger than 61 years, independent of the type of cancer. The presented results verify this statement with a probability of not less than 98%.