Anteroposterior Patterning in Xenopus Embryos: Egg Fragment Assay System Reveals a Synergy of Dorsalizing and Posteriorizing Embryonic Domains
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文摘
Two distinct types of axis lacking embryos resulted from partial deletion of the vegetal part of early one-cell-stage embryos. When the deleted volume was 20–40 % (relative surface area), the embryos underwent ventral-type gastrulation and formed ventral mesodermal tissues. When the deleted volume was more than 60 % , the embryo did not gastrulate nor make mesodermal structures (M. Sakai, 1996, Development 122, 2207–2214). We have designated these two types of embryos as “gastrulating nonaxial embryos (GNEs)” and “permanent blastula-type embryos (PBEs),” respectively. Using these embryos as recipients, a series of Einsteck transplantation experiments were carried out to investigate mechanisms controlling anteroposterior patterning during early Xenopus development. GNEs receiving dorsal marginal zone (DMZ) transplants (GNE/DMZs) elongated and formed posteriorized phenotypes, which had muscle cells, melanocytes, and tail fins. In contrast, PBE/DMZs did not elongate but formed cement glands and brain-like structures showing strong anteriorization. Simultaneous transplantation of the cells from various regions of normal embryos with the DMZ into PBEs revealed that the entire vegetal half of normal embryos, except for the DMZ, showed posteriorizing activity. These results strongly suggest that anteroposterior patterning in Xenopus is not achieved solely by the dorsal marginal zone (the Spemann organizer), but instead by a synergistic mechanism of the dorsalizing domain (DMZ) and the posteriorizing domain (the entire vegetal half except for the DMZ).