Isolated Dorsal Animal Blastomeres of Xenopus laevis Are Capable to Form Mesodermal Derivatives, while the Ventral Animal Blastomeres Differentiate into Ciliated Epidermis Only

Abstract

Isolated two dorsal animal blastomeres of 8-cell-stage Xenopus embryos differentiated in about 24% of the cases into mesodermal structures, while the two ventral animal ones formed exclusively atypical epidermis. Of special interest is the fact that most of the dorsal animal blastomeres without mesodermal structures, differentiated into atypical epidermis with large parts of cement gland. Cement glands could not be detected in the derivatives of the ventral animal blastomeres. In earlier concepts it has been suggested that the animal hemisphere of the amphibian egg is an uncommitted area, which receives its instructions for further determination and differentiation from the vegetal part of the embryo. However, the results, shown in this paper, support the view that the developmental determinants are distributed in distinct gradients already in the early cleavage stages. Although the highest concentrations of these putative determinants are located in the dorsal vegetal area (Melton, 1995) and the dorsal marginal zone, lower concentrations of these substances are thought to be present in the animal part, especially in the dorsal animal hemisphere of the egg and the early embryo. Our results indicate that dorsal animal blastomeres of early cleavage stage embryos possess the capacity to form mesodermal derivatives after their separation from the vegetal hemisphere.