User:Afagan4/sandbox

Article Evaluation
I looked at the article about Embryogenesis. The first thing I noticed when reading through the article was that there was a lack of citations. There were a lot of things listed and facts that lack citations. Additionally, there are only 4 sources listed at the end of the article. Also, the author listed that there is no significant growth during cleavage. We were taught that there is no cell growth, significant or not, during cleavage.

Life Cycle
The life cycle of Xenopus laevis takes roughly twelve months from start to finish. That is, from fertilization to adulthood. It is important to note that the earliest stages of the frogs’ life cycle only take about 24 hours to complete, it is the unique process of metamorphosis that takes the longest. The first stage of the life cycle is fertilization.

Fertilization
Fertilization is the event that sets the entire process of development into motion. In Xenopus it occurs externally, meaning that the male frog disperses his sperm across the eggs in the environment. A single sperm enters the egg and triggers it to revolve so that the animal pole is in its proper position. Without this rotation the gray crescent would not be properly set up and the next step, which is cleavage, would not occur correctly.

Cleavage
Cleavage is the second step of development and is important because it establishes the different poles and makes sure that the organizers are being put in place. Cleavage is what its name implies, separations of the egg without growth of the cells.

Gastrulation is the next step of development and is where the cells in the embryo are moved into their designated locations. The three germ layers are also set apart during this time and the organizer is set up on the dorsal side of the embryo, this is vital to neurulation.

Neurulation follows gastrulation and utilizes the germ layers and organizer set up that occurred during that stage. The early form of the nervous system is set up during this time, it is called the neural plate.

Organogenesis
Organogenesis benefits from the earlier stages because it requires the organizer and nervous system. The three germ layers, which were established during gastrulation, now respond to signaling and set up the organ systems.

Research shows that there are cells that support the germ layers in forming the organs during this time. These cells come from the immune system assist in creating organs such as kidneys.

Metamorphosis
Metamorphosis is the last stage of the developmental process and is a defining moment for Xenopus. The defining characteristics of the tadpole, such as the tail and gills, shrink and are replaced by arms, legs, and useful lungs.

TR hormones have been found to play an active role in the changes that occur during metamorphosis. They are found in the head, middle, and tail regions of the changing tadpole both before and after the change.

Axis Formation
All axis formation is centered around the organizer, which is located on the dorsal side of the developing embryo. The organizer is set up in this location because of the Nieuwkoop center. Axis formation is important to the development of Xenopus because without it the frog would lack proper body formation and more than likely would not survive.

Dorsal/Ventral
The dorsal and ventral body axis are the product of mainly two organizers. The first is Wnt, which signals on the dorsal side of the embryo. The other organizer responsible for setting up this axis is BMP, which is found on the ventral side of the embryo.

Research has been done on the specific forms of Wnt within the embryo and during the setup of the axis. It has been found that Wnt11 work in conjunction with one another to establish the dorsal side of the embryo. It has also been found that Dkk1 assists the two forms of Wnt in influencing only where they are supposed to go. This is achieved by it repressing and initiating the function of Wnt.

Anterior/Poster
Wnt and BMP not only influence the development of the dorsal and ventral axis, they are also the key players in the establishing of the anterior posterior axis. BMP is credited with congregating in the anterior side of the embryo. Wnt, on the other hand is found in the posterior.

Left/Right
The final axis that is present in the developing embryo is the left and right axis. This axis is unique from the others because it is regulated primarily by rotating cilia, whereas the others are set up by repression/expression of organizers. Pitx2 is a left signaling organizer, and as mentioned, it is set up on the left side because of the rotating of the cilia. The cilia are in the node and as it receives the Pitx2 from the organizer is carries it over.

Research has been done on the importance of the placement of the cilia for the equal spreading of the organizer, and therefore the proper setup of the axis. The cilia traditionally develop on the posterior side of the embryo, and carry out their function from there. They receive the signals that they need to develop in this area from Vangl2. It was discovered that if the Vangl2 levels were not held at steady amounts, the cilia grew in a more central location. This completely upsets the spread of Pitx2 and therefore causes the left and right axis to form incorrectly, or not at all.

Life Cycle
The life cycle of Xenopus laevis takes roughly twelve months from start to finish. That is, from fertilization to adulthood. It is important to note that the earliest stages of the frogs’ life cycle only take about 24 hours to complete, it is the unique process of metamorphosis that takes the longest. The first stage of the life cycle is fertilization.

Fertilization
Fertilization is the event that sets the entire process of development into motion. In Xenopus it occurs externally, meaning that the male frog disperses his sperm across the eggs in the environment. A single sperm enters the egg and triggers it to revolve so that the animal pole is in its proper position. Without this rotation the gray crescent would not be properly set up and the next step, which is cleavage, would not occur correctly.

Cleavage
Cleavage is the second step of development and is important because it establishes the different poles and makes sure that the organizers are being put in place. Cleavage is what its name implies, separations of the egg without growth of the cells.

Gastrulation
Gastrulation is the next step of development and is where the cells in the embryo are moved into their designated locations. The three germ layers are also set apart during this time and the organizer is set up on the dorsal side of the embryo, this is vital to neurulation.

Neurulation
Neurulation follows gastrulation and utilizes the germ layers and organizer set up that occurred during that stage. The early form of the nervous system is set up during this time, it is called the neural plate.

Organogenesis
Organogenesis benefits from the earlier stages because it requires the organizer and nervous system. The three germ layers, which were established during gastrulation, now respond to signaling and set up the organ systems.

Research shows that there are cells that support the germ layers in forming the organs during this time. These cells come from the immune system assist in creating organs such as kidneys.

Metamorphosis
Metamorphosis is the last stage of the developmental process and is a defining moment for Xenopus. The defining characteristics of the tadpole, such as the tail and gills, shrink and are replaced by arms, legs, and useful lungs.

TR hormones have been found to play an active role in the changes that occur during metamorphosis. They are found in the head, middle, and tail regions of the changing tadpole both before and after the change.

Axis Formation
All axis formation is centered around the organizer, which is located on the dorsal side of the developing embryo. The organizer is set up in this location because of the Nieuwkoop center. Axis formation is important to the development of Xenopus because without it the frog would lack proper body formation and more than likely would not survive.

Dorsal/Ventral
The dorsal and ventral body axis are the product of mainly two organizers. The first is Wnt, which signals on the dorsal side of the embryo. The other organizer responsible for setting up this axis is BMP, which is found on the ventral side of the embryo.

Research has been done on the specific forms of Wnt within the embryo and during the setup of the axis. It has been found that Wnt11 work in conjunction with one another to establish the dorsal side of the embryo. It has also been found that Dkk1 assists the two forms of Wnt in influencing only where they are supposed to go. This is achieved by it repressing and initiating the function of Wnt.

Anterior/Poster
Wnt and BMP not only influence the development of the dorsal and ventral axis, they are also the key players in the establishing of the anterior posterior axis. BMP is credited with congregating in the anterior side of the embryo. Wnt, on the other hand is found in the posterior.

Left/Right
The final axis that is present in the developing embryo is the left and right axis. This axis is unique from the others because it is regulated primarily by rotating cilia, whereas the others are set up by repression/expression of organizers. Pitx2 is a left signaling organizer, and as mentioned, it is set up on the left side because of the rotating of the cilia. The cilia are in the node and as it receives the Pitx2 from the organizer is carries it over.

Research has been done on the importance of the placement of the cilia for the equal spreading of the organizer, and therefore the proper setup of the axis. The cilia traditionally develop on the posterior side of the embryo, and carry out their function from there. They receive the signals that they need to develop in this area from Vangl2. It was discovered that if the Vangl2 levels were not held at steady amounts, the cilia grew in a more central location. This completely upsets the spread of Pitx2 and therefore causes the left and right axis to form incorrectly, or not at all.