Bottle cell formation in relation to mesodermal patterning in the Xenopus embryo

The appearance of bottle cells at the dorsal vegetal/marginal boundary of X enopus embryos marks the onset of blastopore formation. The conditions lead ing to this epithelial activity were investigated by inducing bottle cells ectopically in the animal region with VegT or different members of the tran sforming growth factor (TGF)-beta family. Morphological studies on the ecto pic bottle cells indicate their close similarity to the endogenous bottle c ells at the dorsal blastopore lip. The subepithelial cells of the induced a nimal region express mesodermal genes in a pattern reminiscent to that obse rved on the dorsal lip. Relating this expression pattern to the position of the ectopic bottle cells leads to the conclusion that bottle cells form in regions of high TGF-beta signalling. The specific inhibitory effects of ce rberus on ectopically induced bottle cells revealed that nodal related grow th factors are the intrinsic signals that elicit bottle cell formation in t he normal embryo. In addition, fibroblast growth factor signalling is an es sential precondition for this epithelial response as it is for mesoderm For mation. We conclude that bottle cell formation in the epithelial layer of t he gastrula is closely linked to mesodermal patterning in the subepithelial tissues. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.