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Transcript of Stem Cells
- They are unspecialized cells.
- They can develop into many different cell types.
-They are capable of dividing, long-term self renewal and poliferating.
-when stem cell divides, each new cell has the potential either to remain a stem cell or become another type of cell with more specialized function. Stem cells Stem cells can use it's special properties to help the body in many ways :
- They serve as a sort of internal repair system in many tissues as they divide to replenish other cells
- Stem cells can be induced to become tissues or organ-specific cells with special functions. Types of stem cells Intoducing Stem Cells Nerve cell Stem Cell Blood Cells Skin Cells Overview Stem cells and their unique properties History of stem cells Embryonic stem cells
a. How are they grown in laboratory
b. laboratory tests used to identify embryonic stem cells
c. How embryonic stem cells stimulated to differentiate Adult stem cells
a. Where are adult stem cells found
b. Tests used to identify adult stem cells
c. What is known about adult stem cell differentiation Induced pluripotent stem
a. what techniques used to produce induced pluripotent stem line
b. why they are the most important discovery in stem cell researches Differences and similarities between embryonic , adult and induced pluripotent stem cells Regulations on stem cells researches Importance of stem cells Embryonic stem cells Adult stem cells Induced pluripotent stem cells History of stem cells 1908
Alexander Maksimow first introduced the term " Stem Cell " 1963
McCulloch and Till discovered presence of self renewing cells in mouse bone marrow 1968
Robert Alan Good transplanted a bone marrow between two siblings and it successfully treated immunodeficiency 1978
Dr. Gregor Prindull and colleagues reported finding haematopoietic stems cells in human cord blood. 1979
Martin Evans and Matthew Kaufman intoduced the term "Embryonic stem cells " 1998
Dr. James Thomson derived the first human embryonic stem cells 2005
Researchers discovered third category of stem cells called "cord-blood-derived embryonic-like stem cells" or CBEs. 2007
Three separate groups of medical researchers showed that normal skin cells can be reprogrammed to an embryonic state, producing what are now called induced pluripotent stem (iPS) cells Embryonic Stem Cells - Embryonic stem cells (ES cells) are pluripotent stem cells derived from the inner cell mass of a blastocyst, an early-stage embryo. Human embryos reach the blastocyst stage 4–5 days post fertilization, at which time they consist of 50–150 cells. - Most Embryonic stem cells are derived from embryos that develop from eggs that have been fertilized in a vitro. Growing Embryonic stem cells in the lab - The process of growing embryonic stem cells is known as cell culture .
- Growing Embryonic stem cells in lab is not easy because it is a fine process and it needs alot of time to poliferate. In addition, the process faces some problems that might kill the growing cells. - Human embryonic stem cells (hESCs) are generated by transferring cells from a preimplantation-stage embryo into a plastic laboratory culture dish that contains a nutrient Steps of growing human ESCs : - The inner surface of the culture dish is typically coated with mouse embryonic skin cells called feeder layer. These cells in the bottom of the culture dish provide the cells a sticky surface to which they can attach. Also, the feeder cells release nutrients into the culture medium if the plated cells survive, divide and multiply enough to crowd the dish, they are removed gently and plated into several fresh culture dishes The process of re-plating or subculturing the cells is repeated many times and for many months. Each cycle of subculturing the cells is referred to as a passage Embryonic stem cells that have proliferated in cell culture for for a prolonged period of time without differentiating, are pluripotent, and have not developed genetic abnormalities are referred to as an embryonic stem cell line. At any stage in the process, batches of cells can be frozen and shipped to other laboratories for further culture and experimentation. Problems faces growing human ESCs : - Viruses and other macromolecules in the mouse cells which cover the inner layer of the dish may be transmitted to the human cells which could ruin the whole embryonic stem cell line.
- It takes a long time to create a Embryonic stem cell line. Laboratory tests used to identify Embryonic stem cells - Scientists test the cells to see whether they match the basic properties that make them embryonic stem cells. This process is called characterization.
- Scientists who study human embryonic stem cells have not yet agreed on a standard specific tests that measure the cells' fundamental properties. However, laboratories that grow human ESCs use several kinds of tests including : - Growing and subculturing the stem cells for many months. This ensures that the cells are capable of long-term growth and self-renewal. Scientists inspect the cultures through a microscope to see that the cells look healthy and remain undifferentiated.
- Using specific techniques to determine the presence of transcription factors that are typically produced by undifferentiated cells.
- Using specific techniques to determine the presence of paricular cell surface markers that are typically produced by undifferentiated cells.
- Determining whether the cells can be re-grown, or subcultured, after freezing, thawing, and re-plating. How are EBCs stimulated to differentiate - EBCs remain undifferentiated as long as they are grown under appropriate conditions.
- There are two kind of differentiation : Natural Differentiation Controlled Differentiation - Researchers have devised ways to grow embryonic stem cells without mouse feeder cells. Solutions : - Natural differentiation occurs when cells are allowed to clump together to form *embryoid bodies then they begin to differentiate spontaneously to form muscle cells, nerve cells, and many other cell types *Embryoid bodies : Rounded collections of cells that arise when embryonic stem cells are cultured in suspension. They contain cell types derived from all 3 germ layers. - Scientists are trying to control differentiation to be able to create cultures of specific types of specialized (differentiated) cells
- Some control mechanisms :
- Alter the surface of the culture dish
- Modify the cells by inserting specific genes Adult Stem Cells - Adult stem cells are undifferentiated cells found amoung differentiated cells in a tissue or organ.
- Adult stem cells roles in a living organism are to maintain and repair the tissue in which they are found, they act as internal repair system.
- Adult stem cells can be called somatic stem cell. Types of adult stem cells Hematopoietic adult stem cells Bone marrow stromal adult stem cells Hematopoietic adult stem cells - They form all the types of blood cells in the body. - Hematopoietic adult stem cells not only give rise to red blood cells, They also give rise to white blood cells and platelets. Bone marrow stromal adult stem cells - This type of adult stem cells make up a small proportion of stromal cell ( Non-blood cells derived from blood organs which are capable of supporting growth of blood cells in vitro ) and can generate bone, cartilage, fat, cells that support the formation of blood, and fibrous connective tissue. Where are adult stem cells found - Adult stem cells have been found in many organs and tissues, including brain, bone marrow, peripheral blood, blood vessels, skeletal muscle, skin, teeth, heart, gut, liver, ovarian epithelium, and testis.
- Adult stem cells found in a specific area of each tissue called "stem cell niche"
- One type of adult stem cells are pericytes which are cells that compose the outermost layer of small blood vessels. Tests used to identify adult stem cells - Adult stem cells are identified by many methods, Scientists usually use one or more of these methods to confirm that the cell is adult stem cells, these methods are :
- label the cells in a living tissue with molecular markers and then determine the specialized cell types they generate.
- remove the cells from a living animal, label them in cell culture, and transplant them back into another animal to determine whether the cells replace their tissue of origin.
- It must be proved that a single adult stem cell can generate a line of genetically identical cells that then gives rise to all the appropriate differentiated cell types of the tissue. Adult stem cell Differentiation pathways - Adult stem cells occur in many tissues and that they enter normal differentiation pathways to form the specialized cell types of the tissue in which they reside.
- Differentiation pathways :
Hematopoietic stem cells give rise to all the types of blood cells such as red blood cells, B lymphocytes, T lymphocytes, natural killer cells, neutrophils, basophils, eosinophils, monocytes, and macrophages.
Bone marrow stromal stem cells give rise to a variety of cell types such as bone cells, cartilage cells, fat cells and other kinds of connective tissue cells such as those in tendons.
Neural stem cells in the brain give rise to its three major cell types: nerve cells (neurons) and two categories of non-neuronal cells.
Epithelial stem cells in the lining of the digestive tract occur in deep crypts and give rise to several cell types: absorptive cells, goblet cells, paneth cells, and enteroendocrine cells. Induced pluripotent stem cells (iPSCs) - Induced pluripotent stem cells (iPSCs) are adult cells that have been genetically reprogrammed to an embryonic stem cell–like state by adding particular genes to cells from the body ( adult cells ) to make them behave like embryonic stem cells.
- Viruses are currently used to introduce the reprogramming factors into adult cells, and this process must be carefully controlled Why is Induced pluripotent stem cells important ? - Its so important because scientists might be able to use them to treat diseases such as heart diseases or Alzheimer. - It will solve the problem of rejection of the transplanted cells because it will be a cell from the same body Differences between embryonic and adult stem cells Embryonic stem cells Adult stem cells - Embryonic stem cells can become all cell types of the body because they are pluripotent.
- Embryonic stem cells can be grown relatively easily in culture.
- Scientists believe that tissues derived from embryonic stem cells are more likely to be rejected after transplantation. - Adult stem cells are limited to differentiating into different cell types of their tissue of origin ( multipotent )
- Adult stem cells are rare in mature tissues, so isolating these cells from an adult tissue is very hard.
- Adult stem cells, and tissues derived from them, are less likely to initiate rejection after transplantation. Stem Cell Niche - It is the place where adult stem cell population are found.
- Understanding the microenvironment around stem cells is as important as understanding stem cells themselves, because The microenvironment regulates the behavior of stem cells and thus can teach us how to control stem cells in culture.
- The niche can act on a stem cell by various mechanisms:
- Direct contact between the stem cell and the niche cells
- Soluble factors released by the niche that travel to the stem cell
- Intermediate cells that ‘communicate’ between the niche and the stem cell.
- Scientists believe that the microenvironment around the stem cells has a great impact on stem cell differentiation to a specific cell type, One of the major factors that stimulates stem cells to differentiate. Embryonic Stem Cells Adult Stem Cells Sources - http://www.labgrab.com/timeline/stem-cell-research-then-and-now - http://stemcells.nih.gov/info/basics/defaultpage.asp Stem Cells Laws - Stem cell laws are the law, rules, and policy governance concerning the sources, research, and uses in treatment of stem cells in humans. These laws have been the source of much controversy and vary significantly by country
- stem cell research using the human embryo is permitted in some countries such as Britain and illegal in some countries such as Germany Canada laws on stem cells researches :
- In 2006, Canada enacted a law permitting research on discarded embryos from in vitro fertilization procedures. However, it prohibits the creation of human embryos for research.
- On June 30, 2010, The Updated Guidelines for Human Pluripotent Stem Cell Research outline that:
- The embryos used must originally have been created for reproductive purposes
- The persons for whom the embryos were created must provide free and informed consent for the unrestricted research use of any embryos created, which are no longer required for reproductive purposes
- The ova, sperm, nor embryo must not have been obtained through commercial transactions Induced pluripotent stem cells (iPSCs) Other uses of Stem Cells - Human stem cells could also be used to test new drugs, new medications could be tested for safety on differentiated cells generated from human pluripotent cell lines. Stem cells future in medical field : - Stem cells will introduce a huge difference in medical field, If only scientists find a reliable way to transplant stem cells into the body without being rejected. Important terms Type of stem cells that can get specialized to all types pf body cells. Ex. : Embryonic stem cells , Induced pluripotent stem cells. Pluripotent : Multipotent : Type of stem cells that can get specialized to many but not all types of body cells. Ex. : Adult stem cells Vitro : Laboratory