Real and simulated microgravity can activate signals stimulating cells to enter the S phase during lens regeneration in urodelean amphibians

Abstract

The model of Wolffian lens regeneration was used to study the effect of microgravity on the proliferative activity of cell giving rise to the regenerating lens. In vivo experiments were performed aboard Russian biosatellites and under laboratory conditions, using clinorotation to simulate microgravity. The data of autoradiographic analysis and BrdU assay showed that exposure to micro- g resulted in a 1.2- to 2-fold increase in the number of cells entering the S phase, compared to that in the on-ground control (1 g). This increase was observed both in the zone of regeneration (the dorsal iris) and in the eye growth zone (the pars ciliaris–ora serrata complex). In the regenerating lens proper, the number of cells entering the S phase was also greater under experimental conditions. This often resulted in an increased size of the lens (compared to the control) and disturbances in its morphogenesis. Along with in vivo experiments, we developed a quasi-in vivo system of iris/lens culturing in vitro in a high-speed miniroller, which allows us now to compare the direct effects of low g and the effects mediated by various body systems on proliferation in the same eye tissues. Probable mechanisms of the influence of newt body systems on lens regeneration upon exposure to microgravity are discussed. A hypothesis is proposed that the key role in this influence may belong to early events in the responses of blood circulatory and immune systems to microgravity.