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Thursday, March 17, 2011

"stretchy pants" and hemidesmosomes

In the movie Nacho Libre',  Nacho is a wrestler (luchador) and likes to wear the "stretchy" pants the luchadors wear.  Living things made out of cells can be very firm like plant structures, but in animals,  cells are very stretchy and can participate in making structures like human skin and other tissues which are very malleable.  In our next topic in class we will discuss how eukaryotic tissue cells communicate with the outside world. Certain outside stimuli involving the extracellular matrix can promote shape change in cells and it can cause them to stretch and contort in ways that seem extreme.  Some cells must be stretched and shaped in order to form the shape of internal organs and for wound healing.  How do you stretch a cell and not break it?  Answer:  very carefully.


In a recent paper in Nature, a mechanism for stretching cells is proposed.  The mechanism centers around fascinating membrane protein complexes called hemidesmosomes.  Hemidesmosomes have been known for quite some time to be attachment structures which attach cells to other cells or the extracellular matrix.  Hemidesmosomes also attach to cytoskeleton components inside cells.  But new studies suggest that hemidesmosomes are also mechanosensors able to detect outside forces which squeeze and stretch cells. Hemidesmosomes communicate with intracellular cell signaling components such as kinases and other proteins.  Here again we have another case where a protein is involved in multiple functions.  The end result of the squeezing and stretching is elongated cells that contribute to the final shape of an internal organ for example during embryogenesis.


1 Review hemidesmosome structure and suggest a mechanism for how they could be involved in cell stretching? 


2 What would be the overal mechanism that would drive the cells to take on shapes which would contribute to the final morphology of an internal organ?


3 How do cells know how much force they can take before they rip apart?

39 comments:

  1. This comment has been removed by the author.

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  2. 1. The hemidesmosomes are composed of two subunits. One part is attached by anchoring fibrils and filaments to the cytoskeleton on the intracellular side. And the other part is attached by anchoring fibrils and filaments to components of the extracellular matrix. Perhaps when the hemidesmosomes sense stretching or pulling, they respond by moving in the same direction as the pulling or stretching force. The hemidesmosomes that are located farther away from the stretching/pulling force will respond differently than the hemidesmosomes that are located closer to the stretching/pulling force. This will result in a greater stretching of the section of the cell membrane that is closer to the stretching force. The hemidesmosomes that are farther away from the stretching force will move very little or remain stationary thereby causing the cell membrane to stretch and change shape.

    3. The more hemidesmosomes that are present, the more stretching or pulling force a cell can take before it rips.

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  3. Elizabeth. Good work. I like your hypothesis.

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  4. For question 2, I once heard of a really important protein called Laminin. Laminin is also found in the basal membrane and "are an important and biologically active part of the basal lamina, influencing cell differentiation, migration, adhesion as well as phenotype and survival" (wikipedia). Laminin is important Could laminin be part of a possible mechanism that establishes where the hemidesmosomes are located?

    According to http://askville.amazon.com/Laminin/AnswerViewer.do?requestId=4925085, "Laminin is extremely important to making sure that your overall body structures hold together. If laminin isn't produced correctly, your muscles may form improperly, giving you a form of muscular dystrophy."

    I do not know how Laminin helps to form tissues and organs but it seems that if the Laminin protein is dysfunctional, then the shape of the organ is also deformed thus Laminin has to have some kind of mechanism that shapes cells, tissues, and organs.

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  5. 1.
    Hemidesmosomes are important structures in connecting the epidermis to the dermis. They link the extracellular matrix and the intermediate filament cytoskeleton. Hemidesmosomes are made of five components: α6β4 integrin, plectin, the bullous pemphigoid antigens BPAG1e and BP180, and the tetraspanin CD151. The α6β4 integrin is made up of two subunits that bind laminin in the extracellular matrix. The β4 subunit passes from the extracellular matrix into the cytoplasm of the cell where it binds to plectin. This plectin molecule is a link between the integrin and the cytoskeleton.
    2.
    One way I think hemidesmosomes may aid in cell stretching is by communicating to the cell via cell signal pathways to increase production of important cell components. The membrane of a cell can only stretch from a folded state to a completely single layer state, therefore there is a limit to the distance it can stretch. Signals from a hemidesmosome may tell the cell to create more phospholipids or membrane proteins so that the cell is able to stretch farther.
    Another possibility is that hemidesmosomes tell the cell to reconstruct their internal cytoskeleton matrix, thus changing the shape of the cell. As the cell is stretched, the hemidesmosome is pulled toward the stretching force, as this happens a signal might be sent to the cell to move cytoskeleton filaments from other areas of the cell and add them to the cytoskeleton filaments attached to the affected hemidesmosomes. For example, if there is a round cell that has hemidesmosomes on its right side being stretched the cell will respond by moving cytoskeleton filaments from the top and bottom of the cell and to the right side. This would cause the cell to increase in length and decrease in height, therefore becoming more oval in shape. This mechanism would keep the hemidesmosomes attached to the cytoskeleton as they are pulled away from it as well as allow for cell morphology (such as columnar cells in the intestines).
    3.
    I’m a little confused about this question, but I think you mean what determines whether a cell rips or stretches (I don’t think the cells “know” how much force they can take). I think it depends on the cells ability to grow, obviously some cells are larger than others which is a big determinant in how far it can stretch. This could also be a reason why some cells are larger than others. The more they are stretched the more they are signaled to increase production of phospholipids, proteins, cytoplasm, etc. and therefore they continue to grow. The time it takes to build and receive these cell items would act as a limit to the stretching of the cell. If the cell can’t keep up with the demand for these products then it will rip.
    Also, it depends on the ability of the cell to reconstruct its cytoskeleton. If the cytoskeleton filaments cannot be moved or built quickly enough the cell will probably rip. The more hemidesmosomes the stronger the signal so a higher number of hemidesmosomes may help increase the speed of the reconstruction process.

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  6. 1. Hemidesmosomes attach one cell to the extracellular matrix and have been linked to forming the skin, cornea, parts of the gastrointestinal and respiratory tract. These complexes are multiprotein and provide cells with cues for their polarization, spatial organization, and tissue organization. They seem to play a big part in cell specialization by stimuli. It has been proposed that hemidesmosomes also send signals out to the cell to modulate the organization of their cytoskeleton and many other organelles. They seem to be a signaling agent as well as a connecting agent. Since it is made up of several proteins, it is plausible. Each protein could have a different function. It has been said that 64 integrin protein is responsible for signaling the cell to change shape.

    2. I’m not quite sure I fully understand this question but we have talked a little about cell specialization and I think that is what you are asking about. These hemidesmosomes seem to be working toward cell specialization themselves. As for an overall mechanism maybe there are other protein groups, similar to hemidesmosomes, that signaling the cell to morph and change into what the body needs.

    3. My hypothesis would be based on the signals it receives. In and of itself the cell would not know but maybe when it is beginning to stretch to much, the integrin protein mentioned above sends out a signal telling it to stop stretching. It’s all in the signaling.

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  7. 1. "Hemidesmosomes are evolutionarily conserved attachment complexes linked to intermediate filaments that connect epithelial cells to the extracellular matrix. They provide tissue integrity and resistance to mechanical forces." I think the cell could grow by making the hemidesmosomes longer. Imagine a blown up balloon with straws inside that make the structure of the balloon. If you had a way to make the straws longer, then you could stretch the balloon.

    2. I think cell signaling, homeostasis, and DNA coding that affects cell specialization would be the key to making the cell change shapes.

    3. I think the cell might be programed to only grow a certain amount and then stop, or else it commits suicide. Also, maybe it could signal for molecules that would make it grow, and then when it has grown enough, it could signal that it was done and to stop sending molecules to make it grow. Just a thought!

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  8. 1. "Hemidesmosomes are a major cell surface attachment site for intermediate filaments at cell-cell and cell-substrate contacts, respectively." They "contribute to the attachment of epithelial cells to the underlying basement membrane in stratified and other complex epithelia, such as the skin, the cornea, parts of the gastrointestinal and respiratory tract, and the amnion." They are beginning to find more evidence that the extracellular matrix affects the function of the hemidesmosome. At the top of the hemidesmosome, there are keratins which link the hemidesmosome to the intracellular space and the anchoring fibrils at the bottom link the hemidesmosome to the extracellular matrix and basement membrane. The hemidesmosome is composed of plectin, a6, b4, BP230, BP 180, CD 151. "The a6 b4 integrin appears to act as a regulatory component by transducing signals that profoundly affect the entire cellular machinery. Hence, hemidesmosome may not only represent structural adhesion complexes, but it may also serve through the a6 b4 integrin as "signaling devices" affecting the cell composition." So through the alpha 6 and beta 4, the hemidesmosome would signal the cell to change shape and stretch itself.
    2. The cytoskeleton is what makes cells take on a certain shape and stay that way to be made into organs. It moves the cells around when things are growing and makes sure that cells maintain the shape they should be. "There are a great number of proteins associated with the cytoskeleton, each controlling a cell’s structure by directing, bundling, and aligning filaments."
    3. I would think that something in the cell would know the cell's own bounds. There must be some kind of signaling process that would be able to tell how much force it would take to rip the cell apart. Perhaps the hemidesmosome will know where the boundary is as to how much it can stretch the cell before the cell is taken apart.

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  9. 1. A hemidesmosome consists of dense plaque on the inside of the plasma membrane with filaments projecting through the cytoplasm. The filaments are made of a dense protein called keratin. The keratin filaments are attached to the extracellular matrix by membrane proteins called integrins. If multiple hemidesmosomes are attached to cell, this could cause the cell to be stretched along parts of the extracellular matrix.
    2. Several parts of the extracellular matrix are responsible for the process of tissue development, which in turn derives organs. In making a functional organ during development, both fibronectins and laminins, which are proteins found in the EMC, are involved. Fibronectins cause pathways to move around during embryonic development, and the cells moving to their respective positions form tissues and organs later in development. Laminin influences both cell migration and differentiation which are vital to organ development. Since both laminins and fibronectins must be connected to both extracellular components and cell receptor proteins, it is possible that they interact with hemidesmosomes.
    3. It has been observed that mechanical stress can be converted by integrins to cytoplasmic signals. If the cell is stretched far enough, the tension on the integrin of the hemidesmosome could start a cytoplasmic signal chain reaction that results in the cell not being stretched any further.

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  10. First, I would like to commend Dr. Francis for linking “Nacho Libre” to cellular biology. That is truly remarkable.
    However, as for the topic at hand:
    1. There are two different parts to the hemidesmosomes, as Elizabeth pointed out. The cell may send out a “help” messenger to the hemidesmosomes to alert them that they need to stretch. The stress that is put upon the cells causes the cells to go into panic mode, and the hemidesmosomes then allow the cell to reach its stretching limit.

    2. I agree with Sean on this. We talked about it in class today. The Laminin is vital in the stretching of skin. Also, could collagen play a part in this? It has a lot to do with helping skin to move and stretch. As people age, so does the collagen and it doesn’t work as well, therefore, older people have wrinkles. Both the collagen and the laminin must play a role in the mechanism of the cells to morph to what they are being pulled to.

    3. We live in a finite world. Nothing goes on forever. My hypothesis would be that the cell will stretch thinly, like gum. If you take gum, you can stretch it out very far, however, there is a point where it does break. Even cells, at their microscopic size, can reach a point where they can no longer stretch any more without breaking. Where this point is, I am not totally sure. It would have to differ between cells. I’m sure different cells are unique, some with stronger membranes than others. There are only so many phospholipids, and they can only be pulled so far apart. Because we live in a world in which a Creator made everything different and unique, therefore no cell could be an exact copy, and they must differ in “stretchyness” am I totally out there for thinking that? Obviously the limit can be exceeded because we get cuts, women in childbirth rip their skin, and if pulled very hard to a point of much discomfort the skin will just rip off.

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  11. 1: Hemidesosomes are asymmetrical and are found in epithelial cells connecting the basal face to other cells. They also have an inner and outer plaque, which serve as an anchoring filament complex. This complex forms a continuous structural link between the basal keratin intermediate filaments and the underlying basement membrane zone, and dermal components. Because the hemidesmosome doesn’t move, the cell membrane will have to move and stretch in order to bind to the HD.
    2: There are cross banded microfilaments in the plasma membrane have loops and collagen fibers which causes them to be stretchy and to change shape and to be able to move. The collagen protein that is in the filaments could definitely contribute to the morphology of the internal organ because of how stretchy it is.
    3: Considering that cells don’t have brains, they obviously can’t ‘know’ per say how much force they can take before they can rip apart, but I think that the cell stretches and the signaling of the cell contributes to tell the cell how much to stretch so that it doesn’t tear.

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  12. After talking in class today, it seems that laminin would be the mechanism that would stretch the cell, in response to question 2. Possibly for some cells it could be collagen, depending on the type of cell that is being stretched. I never really thought about how cells must stretch to do their function until this blog and today's lecture. Interesting stuff!

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  13. 1. Hemidesmosomes have two rivet-like plaques with the anchoring fibrils and anchoring filaments called the Hemidesmosome anchoring complex. It links the filaments and the basement membbrane, also the dermal components.
    3.I think cells will be notified by the signal released by nerve cells since we should feel pain before the cells rip

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  14. going along with what brittney said for question 3, so if the cell only stretches so much and there is a point at which the hemidesmosomes "tell" the cell to stop stretching, is that the point where the cell just rips? There obviously where there is a point where there is too much stress on the cells, therefore they rip? or does the skin just rip between cells?

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  15. 1) It appears that hemidesmosomes are composed of integrins, an alpha subunit, a beta subunit, and an antigen. They also have terminal carboxyl groups for binding. The hemidesmosomes bond to intermediate filaments within a cell, allowing the cell to be stretched when the hemidesmosomes move.

    2) In and of themselves, cells do not necessarily "know" what form to assume. The extracellular matrix (laminin, fibronectin, collagen, etc) can influence the cell to change shape. However, something had to influence the extracellular matrix to shift. Stimulation begets stimulation. Ultimately, something outside of the first living beings (which are places of disequilibrium) had to have started the process.

    3) The issue of how much stretching a cell can take is an issue of the strength of the bonds that hold the different components of the cell together. For example, a cell with many covalently-bonded structures will be stronger than one with many hydrogen-bonded structures.

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  16. 1.) Hemidesmosomes have a plaque anchor on the inside of the plasma membrane which is anchored to transmembrane proteins and the extending keratin filaments by collagen fibers. The keratin filaments adhere integrin in the extracellular matrix. If hemidesmosomes are strategically placed on the cell membrane, they could stretch the cell several different ways.

    2. We just learned in class that a2B3 integrin protein can be turned "on" and "off" so could it be possible that the integrin that the hemidesmosomes bind to can do the same? If this is the case then perhaps hormones can activate the integrin in certain places to allow the hemidesmosomes to bind to them which would stretch the cell in a desired way. It could possibly go the other way too, with the hemidesmosomes being activated or dectiated. Laminin is also important in moving cells to their positions in organ development.

    3. Over stretching causes stress on the cell and stress causes signals to be released. If my guess in my second answer is correct, then stress on the cell could trigger a chemical message that would shut down some hemidesmosomes and prevent further stretching.

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  17. 1. Hemidesomes have two plaque rivets. These it anchor to proteins in the membrane. When the Hemidsomes move, the cell will stretch along with them.

    2. Stimulation must come from the information encoded in the DNA. This leads to a release of a stimulator, probably from the brain. This stimulation produces Hemidsomes which adhere to the extracellular matrix at specific points.

    3. Stress from excessive stretching would cause a release of material. This material could release signals that would stop the Hemidsomes from preforming their function.
    The body could have a track or a external signal that tells the Hemidsomes to stop preforming their function.

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  18. 1 Review hemidesmosome structure and suggest a mechanism for how they could be involved in cell stretching? According the medical dictionary,Hemidesmosome is a specialized structure that attaches an epithelial cell to the basement membrane beneath it. are it there are two plague rivets that are anchored and attached to the proteins within the membrane. when it makes a sudden movement the cell itself will actually move and stretch with it.


    2 What would be the overal mechanism that would drive the cells to take on shapes which would contribute to the final morphology of an internal organ? the motivation and stimulation with come only from the signaling from the DNA, this then would soon lead to sending the brain signals to react to.


    3 How do cells know how much force they can take before they rip apart? Anxiety and nervous stressful situations can cause the release of the material.

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  19. 1.According to "structure and assembly of hemidesmosomes", published by pubmed.gov, states "the hemidesmosome is a complex junction containing many proteins. The keratin cytoskeleton attaches to its cytoplasmic plaque, while its transmembrane elements interact with components of the extracellular matrix. Hemidesmosome assembly involves recruitment of alpha 6 beta 4 integrin heterodimers, as well as cytoskeletal elements and cytoskeleton-associated proteins to the cell surface." Also, the hemidesmosomes interact with laminin-5 to promote the phosphorylation and dephosphorlation of alpha 6 beta 4 integrin. Then, it triggers cystoskeleton andhorage and the hemidesmosome plaque to maintain a firm epitheliah adhesion to the basement membrane.

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  20. 1 Hemidesmosomes are adhesive structures that bind cells to the basement membrane. These structures contain plaque on the plasma membrane with keratin filaments going outward. These filaments link to the ECM by using integrins. These structures are probably involved with cell stretching in that they are attached to the ECM and the cell. This property would allow them to stretch the cell by sending signals via integrins to the ECM to either move the collagen fibers outward stretching the cell, or by disconnecting to the ECM filaments that it is attached to and reattaching to filaments in the ECM that are further away from the cell causing the cell to stretch.

    2 The way that organs are formed is largely due to cell communication and cell specialization. Cells are able to communicate as to which cell will create what and be which part of the organ. These cells then specify their shape by changing into what their role consists of. These Hemidesmosomes are probably a vital role into changing the cell into what its specification requires. Using integrins, these cells would receive signals corresponding to its requirements for the cell in the organ which go to the Hemidesmosomes to shape the cell into its most beneficial structure since structure equals function. All together these cells would form an organ.

    3 The cell is able to communicate with others and itself very efficiently and there is most likely a receptor that the cell is able to release when there is too much stress on a specific entity of the cell which would go to a part of the cell that would react to that receptor so as to release that stress. Most likely there is some part on the plasma membrane that realizes when the cell is overly stressed and sends a signal to the Hemidesmosomes to relax and avoid lysis and cell death.

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  21. 1) Hemidesmosomes are involved in promoting the adhesion of epithelial cells to the underlying basement membrane. They are made of an alpha6-beta4 integrin that is able to transduce signals from the ectracellular matrix to the interior of the cell. This can help modulate the organization of the cytoskeleton. The integrin is made up of two subunits that bind laminin to the extracellular matrix which aids in cell growth.

    3) Too much stressing could cause a signal to be sent to the cell. There would be some type of way to keep the cell balanced and avoid lysis.

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  22. 1. looks like I found the same website as Susan... "hemidesmosomes are the major cell surface attachment sites for intermediate filaments at cell-cell and cell-substrate contacts, respectively. The transmembrane molecules... in the hemidesmosome include the integrin class of cell matrix receptors." I looked up more on the integrin and found that..."The connection between the cell and the ECM may help the cell to endure pulling forces without being ripped out of the ECM."

    2."The laminins are a family of glycoproteins that are an integral part of the structural scaffolding in almost every tissue of an organism. They are secreted and incorporated into cell-associated extracellular matrices. Laminin is vital for the maintenance and survival of tissues. Defective laminins can cause muscles to form improperly.."

    3. I'm going to jump the boat and make assumption that once the cell membrane has reached it's limit in stretching...it would have a system like the human nervous system. It would have something like nerves that make signals to the brain when something is hurting us or whatever...just a thought.

    -Sarah Gonzales

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  23. the movie by far was hilarious. but thats just a side note haha. Ok back to business
    1 Hemidesmosomes are generally have two plaque rivets theses will anchor to some proteins in the membrane acting as a last chance kind of resort in case the lose there grasp on the things around them this anchor is not like the one you per-say would use for your boat it is a sort of slinky because it gives to the plaque allowing it to move around the membrane
    2 what makes the cells take there shape
    It is the DNA which give them the genetic code that is like a steroid that tells the cells what shape to become or what not to become. plus it also tell the body to release the Hemidesomes

    3 cell can tell if your stressing due to the fact that when you stressing out you body release something similar to that of when you get cut the injured part of your body releases that message so that is kinda of what you body does when you are stressing out. then this signal would help your cells to stay even keeled. until you mellow out

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  24. 1. Hemidesmosomes are differentiated sites at the basal surfaces of epithelial cells where the cells are attached to the underlying basement membrane. They contain intermediate filaments projecting into the cytoplasm. A mechanism for how they could be involved in cell stretching, I think is that the protein plectin which is anchored to the integrins in the basement membrane could all work together with the collagen fibers to stretch the basement membrane of the cell. This would take many hemidesmosomes working together but could increase the size of the cell.

    2. I think the overall mechanism of these cells taking shapes is the signaling from the nucleus into the cytoplasm to these filaments in the cells and as well to the proteins in the membrane which can send signals to the extracellular matrix, such as laminin, collagen, etc. which can they morph the cell into the shape it is supposed to take.

    3. I think it depends on how many hemidesmosomes or bonds that hold together the cell for it to know its "breaking point" so to say. I think it also depends on the signaling of a cell to stretch as well to know how much it needs to, to properly carry out its duty.And if too much stress is applied to the cell, there has to be a mechanism or signaling for the cell to stop sending signals to stretch itself.

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  25. The cell adhesion proteins of hemidesmosomes are from the cadherin family and since they can connect to the cytoskeleton of cells the hemidesmosomes could pull and shape cells ito different shapes in this way.
    Ultimately the DNA of cells determines the shape they will end up in. Also, the amount of force a cell can have on it could also be contained in the DNA. That way the cell would “know” how much it could take and would be structured for that amount of pulling and stretching.

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  26. 1. For this one, I think the proteins that connect the extracellular matrix and the intermediate filament cytoskeleton have to do with how the hemidesmosomes stretch the cell...The proteins are what hold the layers together, so if those proteins allow the layers to be squished together or stetched, then that would answer the question on how the hemidesmosomes allow the "stretching" of a cell. Most likely the fibers that stretch have something to do with the proteins that hold it together..not sure though.
    2. I definitely would agree with Kaylynn and Shannon on what the overall mechanism would be. The DNA from the nucleus probably uses signals and receptors to tell the cell what to do when it comes to stretching and becoming smaller. Once it becomes too stressful for the cell, most likely signals are released (like Jordan said) and these signals are then sent back to the nucleus where then new signals are sent to tell it to stop.

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  27. 1. Hemidesmisomes connect the cell to the ECM. They however use integral protiens to do this. Hemidesmisomes use keratin to bond to an intecgrin. This integrin can then attach to laminin, which forms a bond between the cell and matrix. It can however bond to many different types of proteins. It could be possible that the hemidesmisomes are constantly attached to the ECM, but what they are attached to changes regularly. This means that the stretching could take place, but it is still intact. What also happens is that hemidesmisomes contain two plaques, connected using anchoring fibrils and filaments. This could cause the filaments to be "stretchy" allowing for the cell to expand and thus increase the stretchiness of the epidermis.
    2. The ECM basically controls the shape of the organs. This means that the cells are specialized to do what they were designed to do and consequently the ECM changes its hold to meet the needs.
    3. The more hemidesmisomes connecting the cells to the basal surface, the more it will take before the cells disconnect from it. It is likely that a cell signal controls the stretchability of the hemidesmisomes, so when too stressed, it can release it

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  28. 1
    Hemidesmosomes are made up of three classes of proteins: 1) the cytoplasmic plaques, which are bullous pemphigoid antigen 230 or bp 230, plectin, as well as HD 1, IFAP 300, and the protein P2000 2) The second class is the transmembrane constituents of HD, which include the alpha6beta4, integrin, and BP180. 3) The ECM protein laminin 5. The alpha6beta4 is involved in signaling for cell adhesion, which would make sense as to why it is streatchy.
    2
    The alpha6beta4 component would have the impact of the cell shape out of all these units because it is involved with in the signaling for cell adhesion and it would be responsible for where the cell attaches to the ECM.
    3
    I really like Trent's idea, at least it makes the most sense to me. Id there are more adhesion sites to the ECM the cell sin't going to be able to stretch as much and they probably signal to some kind of control center that will send out signals to disconnect.

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  29. I think the mechanism for the hemidesmosome structures that can help them be involved in cell stretching would be part of the five components they consist of. I think the can detect the stretching of the cell by communicating this movement to the cell, which will cause the cell signaling pathways to increase in the production of cell components. They have the cytoskeleton which helps the cell to take on a particular shape which then will be transformed into organs. This cytoskeleton is controlled by proteins that help control this characteristic. I think the cells determine on the force needed before they can rip apart is possibly by how they may be bound or how the hemidesmosome is being pulled. They have signals being sent to the cell to determine this point where they can’t stretch anymore

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  30. Hemidesmosomes are attachment complexes linked to intermediate filaments that connect epithelial cells to the extracellular matrix. http://www.ncbi.nlm.nih.gov/pubmed/20205195 Maybe the “stretchiness” is found in that linking between the cell and the ECM. On either end of the hemidesmosome that attaches to the cells and the ECM there could be sensory proteins or parts that detect signals or sense when the cell is being pulled on. Once it senses the pulling, it can shift itself in a way that allows the cell to be stretched out rather then ripped, kind of like a ball on the end of a rubber band. The ball (cell) is being bulled on, but the rubber band (hemidesmosome) is responding so it allows a certain level of stretch before the cell would burst. I’m guessing the hemidesmosome knows how far it can stretch by way of signaling, possibly in those same sensors I proposed earlier. Just like in a rubber band you can tell when its being stretched too thin because its starts to crack and stretch more slowly, maybe the hemidesmosome can tell how far it can stretch based on rate at which it stretches, or physical resistance .

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  31. 1 Hemidesmosome are specialized junctional complexes that contribute to the attachment of epithelial cells to the underlying basement membrane in stratified and other complex epithelia. These multiprotein complexes determine cell–stromal coherence and provide cells with cues critical for their polarization, their spatial organization, and for tissue architecture. A mechanism for cell stretching may be due to the spatial organization. It has space to move around and stretch.
    2 Although these structures appear relatively stable, which would counteract cell migration and displacement, their functional activity can be modulated. The regulation of the adhesive interactions of hemidesmosome with the underlying basement membrane is essential in various normal biologic processes, such as wound healing and tissue morphogenesis. This is why the shape is so crucial so the internal organ can heal.
    3 The cells will know how much force they can take based on what was already mentioned the cells are very organized and spaced out. The structure is also very precise so it makes it very easy for the cell to dictate when it’s going to rip.

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  32. As the first question has been quite thoroughly answered...
    2. I agree with Erik on how cell stretching is controlled by DNA. The laminin is coded in such a way that it will either signal the cell to stop growing or could it possibly detach from the hemidesmosome?
    3. I think how far a cell stretches is determined by the function of laminin which binds to the hemisdesmosome. The point at which a cell no longer receives signals to increase its size is probably predetermined in the DNA. One thing I wonder about is how the laminin would feel enough stress to stop signalling the cell if the cell is growing, and so relieving the stress. Perhaps another set of signaling is involved as well, like interactions between neighboring cells.

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  33. 1. Hemidesmosomes are rivet-like structures that connect the cell to the EM. If they moved, or sensed movement, they could stretch the cell along EM. Because the HD-anchoring filament complex forms a continuous structural link between the basal keratinocyte keratin intermediate filaments and the underlying basement membrane zone, communication and synchronized movement is possible.
    2. From what I remember, the extracellular matrix is what guides and directs most cell activities. The cytoskeleton also plays a large roll in cell morphology.
    3. I know that desmosomes help cells not rip apart, and it specializes in cell-cell adhesion. In addition to that, when a cell overexerts itself it can send signals in ECM that stops the stretching.

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  34. Hemidesmosomes are small structures that contain integrin that underlies the basement membrane serving s an anchor. Hemidesmosomes work with integral proteins and the extracellular membrane to stretch such as laminin, which gives the cell potential for migration, growth, and differation but uses the proteoglycans to keep its strength and resistance to not burst. The extracellular membrane (collagen, proteoglycans, ficronectin, and laminin) are the main determining factors of what the cell’s shape is, such as in red blood cells mutation will cause sickle cell anemia. To prevent from growing to large, the cell would most likely send a signal to either get larger or try and maintin things being taken in. Cell division could also prevent this.

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  35. 1. Attaching cells to the extracellular space, Hemidesmosomes link in a way to form certain structures and parts. These have multiple proteins and signal cells when they are to do stuff such as polarization, spatial organization, and organization of tissue. This seems to be a major player in the specialization of cells by stimuli. These same signals tell the cell to modulte the organization of their cytoskeleton and other things such as organelles. Somehow a both a signaling agent and connecting agent are involved..

    Will try to come back if research goes well on the other two questions, otherwise, I'll just answer number 1 for now. :)

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  36. the attachement of the cells of the etracellular matrix is of crucial importance in the maintenance of tissue structure and integrity.hemidesmosomes are involved in promoting the adhesion of epithelial cells in the underlying basement membrane.

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  37. After looking at the structure of the hemidesmosomes, the integrin that link the keratin filaments of the hemidesmosomes and the extracellular matrix, transmit signals from the ECM that affect the shape of the hemisdesmosome.

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  38. 1) hemidesmosomes anchor cells to their underlying basement. They contain a plaque on the inner-plasma membrane with filaments that stick out into the cytoplasm. These filaments are comprised of keratin. These intermediate-filaments serve a supportive function primarily. These filaments are attached to the basement membrane by integrins which can transmit signals from the Extracellular Matrix to the cell that inform the cell on how to form its shape and its activities. I imagine that when the cell receives signals from the ECM via the integrins/intermediate-fillaments (keratin) and the cell reacts by stretching itself.

    2)I think it would start with the DNA in the individual cells. After a cell has been differentiated, the DNA would encode all of the details necessary for a cell to develop and shape into the necessary form for the tissue. The cell is connected to the basement membrane via hemidesmosomes, which can accept signals from the EMC. The EMC might contain messages encoding cells to form a certain way or stretch a certain way to get into the necessary form. The variety of EMC proteins (including selectins which bind to the oligosachharides from other cells, IgSFs which act in cell-cell adhesions, and adherins which are Ca+ dependent cell-cell adhesions and transmit signals) provide a vast network of encoding information that tells the cell how to shape itself.

    3)Because of the vast internetworking of the EMC and the ability for the hemidesmosomes to receive cell signals via keratin and integrin, the cells probably receives a signal from tension-dependent sensor that signals the EMC that it can no longer receive stress without ripping.

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