![]() In this way, an embryo goes from a single cell type to multiple distinct cell layers. Other outer layer cells epibolize to cover these internalizing cells. In general, gastrulation involves the involution and invagination of outer-layer cells to become internalized. An editable svg file of this figure can be downloaded at ![]() The donor tissue primarily forms the notochord. Most of this second body is made of host tissue. Transplantation of the dorsal lip of the blastopore from a donor to a host of a closely related species gave a second body axis. Figure 6: The Spemann-Mangold experiment. 2) The notochord patterns the tissue around it to make the primary body axis 15. This meant two important things: 1) The dorsal lip of the blastopore develops into the notochord. They found that only a tiny portion of the twinned tadpole tissue was unpigmented - the notochord (plus some additional cells here and there - the technique was not completely perfect). In this way she was able to see which tadpole tissues came from the donor (the unpigmented newt) and which from the host (the pigmented newt). Mangold took the blastopore lip from an unpigmented newt species and transplanted under the ventral ectoderm of an early gastrula pigmented newt from the same genus. Soon Spemann revised his hypothesis, largely based on careful observation of gastrulating embryos and on the cross-species transplantation work by Mangold. When he transplanted the dorsal lip from one newt to another, he got conjoined twin newts - suggesting that some signal from the dorsal lip was indeed patterning the main body axis 12,13. Spemann thought he had support for this hypothesis when he did transplantation experiments in newts. Without this signal, cells wouldn't differentiate. One possibility was that a morphogenic signal emanated from the dorsal lip that caused cellular differentiation in a time gradient, such that the closest cells to the dorsal lip differentiate first. He knew it was important because if he sliced an embryo in two, the half that got the dorsal blastopore lip developed into an tadpole, while the other half developed into a "belly piece." He also knew that if he carefully divided the embryo down the middle of the dorsal lip of the blastopore, both halves would develop into a tadpole. Spemann had wondered for years what exactly the dorsal lip of the blastopore did. Hans Spemann and his graduate student Hilde Mangold perfected a technique to do cross species transplantations of the dorsal blastopore lip to new locations in the host's body. The movie ends as the neural plate and neural folds become visible.\) This movie was morphed by Steven Black from the original drawings of Xenopus laevis gastrulation made in Downloaded from Hardin'sīased on drawings of Nieuwkoop and colleagues Note the elongation of the spinal cord and brain. This movie is a continuation of the movie above, showing the process of neurulation. Xenopus gastrulation and neurulation (external view) ![]() Movie was downloaded from Hardin's Amphibian Development The blastopore constricts, note the rotation of the embryo so that the dorsal midline comes to lie on top. ![]() The blastopore then quickly expands to its full circumference. The future lateral and ventral lips of the blastopore are visible asĪ ring of pigment at the start of the movie. Involution site at the start of the movie. Note the ring-shaped blastopore through which cell layers involute. This movie views a gastrulating Xenopus laevis embryo, looking at the blastopore from a dorsal and posterior Note the anterior extension of the involuting mesodermal cells. Note the diminishing blastocoel and expanding archenteronĪs cells flow into the interior of the embryo. Lip of the blastopore can be seen forming at ~4 O'clock. This movie is of an internal view (mid-sagital section) of a gastrulating Xenopus laevis embryo. Frog gastrulation movies Movies of Frog Gastrulation Click on one of the movies listed in the left column to launch a movie Notes: 1) If you get a dialog box indicating a possible security hazard, choose "open it"Īnd continue 2) Use the "Back" button on your browser to return to this page after viewing a movie. ![]()
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