The behaviour and function of bottle cells during gastrulation of Xenopus laevis

The behaviour of bottle cells in normal and microsurgically altered gastrulae and in cultured explants of Xenopus laevis was analysed, using time-lapse micrography, scanning electron microscopy (SEM) and cell tracing with fluorescein dextran amine (FDA). The results shed new light on the function of bottle cells. Bottle cells forming in vivo show a predominantly animal-vegetal apical contraction and a concurrent apical-basal elongation, whereas those forming in cultured explants show uniform apical contraction and remain rotund. Bottle cells forming in embryos with fewer subblastoporal cells contract more uniformly than those in normal embryos and release of normal bottle cells from supra- and subblastoporal cells results in immediate loss of the bottle shape. These results, and an analysis of the effects of bottle cell formation on the shapes and movements of surrounding tissues, show that unique shape of bottle cells and their probable function in development are not intrinsic properties but result from a modulation of the effect of a uniform and intrinsic apical contraction by the geometric and mechanical properties of the surrounding tissue. Mechanical simulations of bottle cell formation, using the finite element method, suggest how the site of bottle cell formation and the thickness and stiffness of adjacent tissues might change the effects of their formation. These results and FDA marking of prospective bottle cells and the adjacent deep mesodermal cells suggest that bottle cells function during their formation to initiate the involution of the prospective mesodermal mantle. Later they respread to deepen the archenteron and to form its peripheral wall.