The inducing capacity of the presumptive endoderm of Xenopus laevis studied by transfilter experiments

Abstract

The inducing capacity of the vegetal hemisphere of early amphibian blastulae was studied by placing a Nucleopore filter (pore size 0.4 μm) between isolated presumptive endoderm and animal (ectodermal) caps. The inducing effect was shown to traverse the Nucleopore membrane. The reacting ectoderm differentiated into mainly ventral mesodermal derivatives. Expiants consisting of five animal caps also formed dorsal mesodermal and neural structures. Those results together with data published elsewhere suggest that, in addition to a vegetalizing factor, different mesodermal factors must be taken into consideration for the induction of either the ventral or the dorsal mesodermal derivatives. The neural structures are thought to be induced by the primarily induced dorsal mesodermal tissue. Electron microscopic (TEM) examination did not reveal any cell processes in the pores of the filter. The results indicate that transmissible factors rather than signals via cytoplasmic contacts or gap junctions are responsible for the mesodermal induction of ectodermal cells. The data support the view that in normogenesis the mesoderm is determined by the transfer of inducing factors from vegetal blastomeres to cells of the marginal zone (presumptive mesodermal cells).

The Dorsalization of Spermann's Organizer Takes Place during Gastrulation in Xenopus laevis Embryos

“…That means that the caudalization of the chordamesoderm takes place after the early mid gastrula stage, perhaps by reciprocal interactions of the neural plate towards the chordamesoderm (14). Our hypothesis that the dorsalization of the dorsal marginal zone takes place during gastrulation is supported by our earlier transfilter experiments (16). When the vegetal part of a middle blastula including the dorsal vegetal part (Nieuwkoop center) is separated from isolated competent ectoderm (animal caps) by a nucleopore filter, the presumptive endoderm will trigger the ectoderm to form ventral mesoderm structures as coelomic epithelium and blood like structures only.…”

Lithium-Sensitive Production of Inositol Phosphates During Amphibian Embryonic Mesoderm Induction

“…Changes in cell shape and rapid increases in actin polymerization are early cellular responses to stimulation by chemoattractants or growth factors (1,2). Although the signaling pathway is unclear, it may include phospholipid metabolism, especially phosphatidylinositide (PI) turnover.…”

Short-Range Signaling by Candidate Morphogens of the TGFβ Family and Evidence for a Relay Mechanism of Induction

“…cess over levels necessary for mesoderm induction (data not shown). Therefore, although the mesoderm inducers are soluble and can diffuse through filters (Grunz and Tacke, 1986; When activin-FLAG (actFLAG) and AVgFLAG were compared (Figures 1A and 1B), no significant difference Slack, 1991), they may be inhibited from diffusing in the intact embryo by specific interactions with the extracel-was observed. Likewise, no significant difference was observed between different parts of the embryo (Figure lular matrix.…”