Differentiation during Cleavage in Xenopus laevis. I

Abstract

1) The dorsal marginal zone of Xenopus laevis embryos at st. 6, 61/2, 7, 8 and 9 was dissected out and cultured in vitro.2) At st. 6, only one explant, presumably taken from an unusually premature embryo, developed into axial organs, some other specimens forming sucker.3) The capacity for self-differentiation of the zone into mesodermal axial organs becomes conspicuous at st. 61/2. Embryos with this capacity increases at st. 7 and come to the full at st. 8.4) It is concluded that, as in Triturus, the capacity for self-differentiation of the dorsal marginal zone is not preexistent in Xenopus embryos but is aquired during cleavage; i.e. at st. 61/2 to st. 8, a little earlier than in Triturus.5) The first appearance of this capacity precedes the rapid synthesis of “heterogeneous” RNA recently reported, while the rapid increase in the percentage of embryos with this capacity during st. 7 and st. 8 is parallel with the latter.