So, How DID that Salamander Grow His Leg Back?

There are three stages to the limb regeneration. Week 1 is De-differentiation. As we know de-differentiation is the un-specialization of the cells. This happens after a trauma has occurred to the salamander. During this cells such as muscle cells and nerve cells lose the characteristics that make them special.

Week 3 is the Blastema Formation. At this point the de-differentiated cells move to the wounded area and form a blastema, a growing mass of undifferentiated cells. At this point the salamanders body is mimicking what happens at the embryo stage of birth.

Week 5 is the Re-differentiation of the cells. Cells in the blastema then re-differentiate and the cells start creating the tissues needed for the new limb to grow. the cells go through several rounds of Interphase and Mitosis to create more and more cells. The cells continue to go through re-differentiation and in no time the salamander has a fully functioning new leg!!

 Check out this video of a salamander growing it's leg back!

 Google images provided pictures and information is credited to Biology by Joesph  Levine and Kenneth Miller.(ch10)

The Internal and External Factors that Influence the Cell Control System

Cyclins are the proteins that regulate the cell cycle. These proteins are used for Internal and External Regulators.
Internal Regulators are a group of proteins that respond to things happening inside the cell. These regulators allow the cell cycle to proceed but only when each stage has been competed. For example, one regulatory protein prevents the cell from entering Anaphase until the spindle fibers have attached the chromosome.

External Regulators are proteins that respond to events outside the cell. These regulators decide whether the cell cycle needs to speed up or slow down. One group of external regulatory proteins are called Growth Factors which stimulate the growth and division of the cell.

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The Process of Cell Specialization and De-Specialization .

Cell specialization is also called Differentiation, which is the process of a cell becoming more specialized. Remember our friend the stem cell and how he could become any cell he wanted if her received the proper signal? Well once a stem cell becomes a red blood cell or a bone cell it's become differentiated. This means that bone cell can only divide to make more bone cells. Stem cells can become bone cells, red blood cells, skin cells, nerve cells and skeletal muscle cells.

De-specialization is when a cell becomes less specialized.  So when a salamander loses his leg that bone cell goes through De-Differentiation. That means it can go back to being a stem cell. A stem cell can even go through Re-Differentiation, meaning that a stem cell can return to only being a multipotent cell.

Before a cell goes through differentiation it's Pluripotent. That means it can develop into most any cell. After the stem cell differentiates it's multipotent.

 Credits of picture to Scientific American

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The Process That Occurs During Mitotic Cellular Division

The first phase is called Interphase, which is a stage of growing that contains G1, S, and G2 phases. G1 is growth, S is DNA replicating, and G2 is the preperation for division. 


 After Interphase we enter the stage called Mitosis.

 The first stage in Mitosis is Prophase which is only entered once the cell decides it's ready to divide, it is the longest of the 4 stages. First the nucleus condenses and the duplicated chromosomes, or DNA, become visible. Meanwhile spindle fibers form outside the nucleus, these fibers segregate the chromosomes.

Our next phase is Metaphase which is generally the shortest of the 4 phases. The centromeres of the duplicated chromosomes line up across the cell center. Spindle fibers then connect the centromere of each chromosome to the 2 'poles' of the spindle.
Here is a diagram of the metaphase, displaying the centromere and spindle fibers.

Then we have Anaphase. The sister chromatids, copies of the original chromosome, move apart and separate. Each sister cell now contains a chromosome. The chromosomes then separate. Each sister cell now contains a chromosome. The chromosomes then seperate and move along the spindle fibers to opposite ends of the cell. Anaphase can only end when the chromosomes are in 2 separate groups. 

Finally we reach the last stage of mitosis, Telophase. The chromosomes, where were distinct and condensed, begin to spread out into a tangle of chromatin. Nuclear envelops re-form around each cluster of chromosome. The spindle fibers the begin to break apart and a nucleus becomes visible in each daughter cell.

Now, mitosis is done however we still have one more step to complete cell division. That last step is called Cytokinesis. Cytokinesis is the finally split of the two daughter cells. This stage occurs at the same time as telophase.

We now have two fully functioning cells from our original cell.


Here is a diagram of the entire process to help you get a visual image. Image provided by Living Science Mater Experiment.

 Google images provided pictures and information is credited to Biology by Joesph  Levine and Kenneth Miller.(ch10)

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Cellular Division in Reproduction, Growth and Repair

When your in your embryo stage of development you contain only one kind of cell, a stem cell. A stem cell has the potential to become any kind of cell because it has the genes required to do so. But first we need to understand how we get these stem cells.
When a sperm cell first reaches the female's egg the pronuclei of both cells are replicated and joined together after the pronuclear envelops dissolve. The cells then enter Mitosis as the inner DNA or Chromosomes are separated to opposite sides of the embryo, forming the nuclei of two new cells. These new cells are called Topipotent Stem Cells and they still hold the potential to become anything. These stem cells remain topipotent through several rounds of division. Once the blastocyst, a hallow ball of cells, forms the potency of these stem cells changes. Through differentiation, a stage of cell specialization, you get ICM cells and the placenta. ICM cells make up the fetus while the trophoblast cells form the placenta.
Now that these cells have gone through differentiation they have different potency levels. The cells are now Pluripotent Stem Cells. Through more differentiation and divisions we get Multipotent Stem Cells, and again the potential of these cells is even more limited. Then, finally, we get Unipotent Cells. Reaching the unipotent stage means these cells can only divide to give more cells of the same type.

Cells differ in their potential ability and as these cells differentiate they become more and more limited in what they can do.

*the blue you see in the meter under the words represents how much potential the cells have at that stage. The purple is what they can't do.

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