Proliferation and differentiation of Xenopus A6 cells under hypergravity as revealed by time-lapse imaging.

Xenopus laevis A6 cells, which are cloned epithelial cells from the Xenopus kidney, differentiate into a dome structure when the cells reach confluence. We investigated the gravitational responses of A6 cellular motility during normal differentiation and differentiation under hypergravity conditions using centrifugation (1-100 x g). Progression to dome formation was analyzed by time-lapse micrography. Dome formation and increased expression of Na(+)/K(+)-adenosine triphosphatase were used as markers of differentiation. Interestingly, a high rate of cellular proliferation was observed at a low level of hypergravity (5 x g). Despite this, there was no difference in the time to dome formation between the control cells at primary cell density and those that differentiated under hyper- or hypogravity conditions. In conclusion, this experiment on amphibian cells revealed that the proliferation of A6 cells was strongly affected by gravity conditions, but the differentiation step appears to be controlled by an intra- or intercellular clock.