A developmental biologist at Penn's School of Veterinary Medicine, Jean-Pierre Saint-Jeannet, along with a colleague, Young-Hoon Lee of South Korea's Chonbuk National University, has mapped the embryonic region that becomes the part of the heart that separates the outgoing blood in Xenopus , a genus of frog.
Xenopus is a commonly used model organism for developmental studies, and is a particularly interesting for this kind of research because amphibians have a single ventricle and the outflow tract septum is incomplete.
In higher vertebrates, chickens and mice, the cardiac neural crest provides the needed separation for both circulations at the level of the outflow tract, remodeling one vessel into two. In fish, where there is no separation at all between the two circulations, the cardiac neural crest contributes to all regions of the heart.
The blood separation comes from an entirely different part of the embryo, known as the 'second heart field. To determine where the neural crest cells migrated during development, the researchers labeled the embryonic cells with a fluorescent dye, then followed the path those marked cells took under a microscope.
We let the embryo develop normally and look where those cells end up in the developing heart," said Saint-Jeannet. Advanced Search. ISBN s. Customer Review Publication Date. Best sellers in Books See more Previous page. Board book. Next page. There's a problem loading this menu right now.
Learn more about Amazon Prime. Get free delivery with Amazon Prime. Back to top. Get to Know Us. Amazon Payment Products. These classic experiments, for which Spemann received the Noble prize in , focused the attention of a generation of developmental biologists on the "organizer".
Mangold died in a freak accident in , as a graduate student, before her experimental results were published. What cells have "organizer" properties?
How do these cells acquire these amazing "organizing" abilities? What are the molecular signals from the organizer cells that induce the axial patterns of cell fate restrictions? The search was on for the molecules responsible for organizer identity and function. Slowly but surely a molecular model of organizer specification and function has emerged. Maternal mRNA have been found localized to the vegetal pole.
Further, beta-catenin was found to be enriched in the dorsal blastomeres. The experiments below by Spemann and Mangold further illustrate this by testing the inductive abilities of archenteron roof tissure endoderm and mesoderm taken from various anterior to posterior positions in an embryo just after the end of gastrulation. The archenteron tissue is again transplanted into the blastocoel of an early gastrula. Note that the "extra" structures that are induced correlate with the anterior posterior position of the donor archenteron tissue.
Amphibian Axis Formation. Historically, animal development has been thought to be either mainly mosaic and lineage dependent or regulative and dependent on position. Animals like Drosophila and C. If you ablate a C. In contrast, if you ablate a cell in the early embryo of an animal like the frog you often see no effect on development. The remaining cells can alter their fate based on their new neighbor relationships position within the embryo and compensate for the missing cell's progeny.
However, as we begin to understand the molecular mechanisms underlying a cells potency and progressive cell fate restrictions we see that there is no fundamental difference between mosaic and regulative development.
All animals use a spectrum of molecular mechanisms to regulate different stages of cell specification and differentiation. In the figure at right showing the first cleavage of a frog embryo you see the results of isolating the blastomeres. Normally, the first cleavage bisects the "gray crescent". Isolated blastomeres give rise to perfectly normal duplicated embryos.
However, if you experimentally alter the first cleavage so that one blastomere gets all the gray crescent cytoplasm and the other gets none, then the isolated blastomeres behave very differently.
The one receiving the gray crescent material develops into a normal embryo, but the other forms a disorganized mass of tissue called a "belly piece" because it contains mainly ventral tissues. This suggests that some important cytoplasmic determinants are localized in the early vertebrate embryo. We are interested in the same questions that we addressed in Fly development. Where do the first asymmetries arise in vertebrate development? How are the anterior-posterior and dorsal-ventral axis established?
How does embryonic patterning arise? When you look at a frog egg you can clearly see one maternally derived asymmetry. The animal-vegetal axis is obvious due to the pigmentation and yolk differences that are determined during oogenesis. Except for the isolation experiment described above, most experiments on frog blastula and early gastrula stage embryos suggested that cell fate was not determined until the mid gastrula stage.
The transplantation experiments shown at right illustrate this. Heterotopic transplantations of early gastrula tissue resulted in a normal embryo. The transplanted tissue "depended" on its new host neighbors to tell it how to develop Dependent "conditional" development. The embryo's hatching glands are on its snout, so it can direct this concentrated jet of chemicals at a single target, quickly opening an escape hatch and making a swift getaway.
How swift? During actual attacks from predators, the researchers saw embryos hatch in less than 6 seconds, Warkentin said in a statement.
It wasn't just snakes that the embryos could sense — Cohen explained that they observed similar evasive maneuvers in response to wasps, pathogenic fungus and flooding. Their discovery casts embryos in a whole new light, Cohen noted, revealing them to be capable of far more complex behavior than once thought.Strucure in frog embryos that forms accross from the site of sperm entry. color is because the cytoplams of the embryo rotates after fertilization, resulting in a mix of color between the dark animal and light vegetal. Do frog embryos have a primitive streak?