Stem Cells and Cellular Differentiation PDF

Stem Cells and Cellular Differentiation 3.2 In previous studies, you learned that all multicellular organisms start as a single cell. This single cell is sometimes called a zygote. A long process of development is nee...

Stem Cells and Cellular Differentiation 3.2 In previous studies, you learned that all multicellular organisms start as a single cell. This single cell is sometimes called a zygote. A long process of development is needed to transform the zygote into a fully formed plant or animal. First, it goes through a series of divisions that generates many cells. As the cells of this early-stage organism, known as an embryo, continue to divide, the cells begin to show differences in their shapes, contents, and functions. In other words, the cells become specialized. The process that produces specialized cells is cellular differentiation. cellular differentiation the process Cellular differentiation is directed by the genetic information inside the by which a cell becomes specialized to perform a specific function cell. This genetic information is encoded in the cell’s DNA. It is passed from parent to offspring in the eggs and sperm cells. Stem Cells In animals, a cell that can differentiate into many different cell types is called a stem cell. A stem cell divides into two daughter cells through the processes of stem cell an undifferentiated cell that mitosis and cytokinesis (Section 2.5). Each resulting daughter cell can develop can divide to form specialized cells into a different type of cell, based on which parts of its DNA are switched on (Figure 1). Stem cells generally occur in clumps that differentiate into different tissue layers, such as epithelial, muscle, and nerve tissues. expression of genes specific to skin cells skin cell two daughter cell cells with the division same genes stem cell nerve cell Figure 1 In this example, each expression daughter cell differentiates into two of genes specific different types of specialized cells: to nerve cells a nerve cell and a skin cell. There are two types of stem cells. Embryonic C03-F08-UAOS10SB.ai stem cells can differentiate into any kind of cell. Tissue stem cells (sometimes called “adult stem cells”) exist within specialized tissue. They are only able to differentiate into certain types of cells. For Illustrator Joel and example, tissue stem cells foundSharon Harrismarrow can in bone differentiate into white blood cells, red blood cells, or platelets (Figure 2). This is why bone marrow transplants are often a successful way to treat cancers Figure 2 This cross section of bone shows the spongy bone tissue. that affect blood cells. The spaces are filled with bone marrow. NEL 3.2 Stem Cells and Cellular Differentiation 77  RESEARCH THIS STEM CELL RESEARCH In CAnADA SKILLS: Researching, Analyzing the Issue, Communicating, Evaluating SKILLS HANDBOOK 4.A., 4.C. Many medical experts believe that stem cells can be used to treat 3. Research the ethical arguments for and against stem cell a variety of injuries and illnesses. This field of medicine is called research. “stem cell research.” Researchers are considering the use of stem GO TO NELSON SCIENCE cells in the treatment of spinal cord injuries, Parkinson’s disease, Alzheimer’s disease, diabetes, multiple sclerosis, and heart A. Summarize Canada’s current guidelines for stem cell disease. There are many practical challenges in this line of work. research. T/I Human stem cell research is also full of legal, ethical, and B. Write a short report on one possible application of stem cell social concerns. Many nations have developed ethical and legal research. T/I C A guidelines for research that involves human stem cells. C. Summarize the ethical arguments relating to this application 1. Investigate Canada’s current guidelines on stem cell research. of stem cell research. Present your position in an appropriate format, supporting your opinion with reasons. T/I C A 2. Identify and research one possible future medical advance that could result from stem cell research. Cord Blood Cell Banking The blood found in the umbilical cord immediately following birth is a rich source of stem cells. These are not embryonic stem cells; they are more similar to tissue stem cells. They can develop into any of the various kinds of blood cells. Umbilical cord blood has a high concentration of these tissue stem cells and is relatively easy to obtain (Figure 3). This collected blood could be “banked” (stored) in case it is needed later in the child’s life. Current uses for such cord blood stem cells include treatment for childhood cancers such as leukemia. DID YOU KNOW? Canadians and Stem Cell Research Research in the stem cell field grew out of findings by Canadian scientists Ernest A. McCulloch and James E. Till in the 1960s. GO TO NELSON SCIENCE Figure 3 Umbilical cord blood collection Some commercial companies sell the service of cord blood banking. They promote the idea that the child, or a sibling, may benefit from a future treatment using these tissue stem cells. Many new parents are asked whether they want to bank their new baby’s cord blood. 78 Chapter 3 Animal Systems NEL Tissue Stem Cell Transplantation Both cord blood and bone marrow stem cells are relatively easy to isolate. Both have been used to treat diseases such as leukemia. Leukemia is a cancer that occurs in the bone marrow. The stem cells that differentiate into blood cells divide too quickly, resulting in non-functioning blood cells. In leukemia treatment, all of the diseased white blood cells must first be removed and the bone marrow must be killed. Chemotherapy can target and kill bone marrow cells and white blood cells. Healthy bone marrow cells (or stem cells collected from the blood) are obtained from a carefully matched donor. The healthy stem cells are then injected into the patient’s blood. In a successful stem cell transplant, the donor blood stem cells grow in the patient’s own bone marrow. Eventually, they produce healthy, cancer-free blood cells. Regeneration and Tissue Engineering In complex animals, such as mammals, the term “regeneration” refers to the ability of a tissue to repair itself. Skin, muscle, and bone can regrow and heal after an injury. Not all cells regenerate, however. Nerve cells, for example, do not naturally regenerate completely. In animals such as salamanders, sea stars (starfish), and flatworms, regeneration can sometimes replace lost limbs and even large portions of the body (Figure 4). Scientists are researching ways to regenerate human body Figure 4 Some species of starfish have tissues and parts that do not normally regenerate. This field of research is an extraordinary ability to regenerate. called tissue engineering. This is useful in treating spinal cord injuries and A single severed “arm” can grow into a in different types of tissue grafting, which involves providing replacement whole new starfish. tissues for patients. Tissue engineering could also provide a source of To find out more about advances biological models for testing drugs and other potentially dangerous in tissue engineering, substances. GO TO NELSON SCIENCE In SUMMARY Cellular differentiation is the process by which a Stem cell research is discovering medical less specialized cell becomes a more specialized treatments for injuries and diseases. cell type. Regeneration results in the repair or replacement The two types of stem cells are embryonic stem of tissues or body parts. cells and tissue stem cells. CHECK YOUR LEARnIng 1. What is the meaning of the term “cellular 4. What is the significance of being able to harvest stem differentiation”? K/U cells that can specialize into any type of cell? K/U 2. What is the difference between tissue stem cells and 5. Briefly describe the process of a bone marrow transplant embryonic stem cells? K/U to treat leukemia. K/U 3. Why are stem cells from a newborn baby’s umbilical cord 6. How is regeneration beneficial to an animal? K/U blood considered to be tissue stem cells? K/U 7. Can all animals regenerate? Explain. K/U NEL 3.2 Stem Cells and Cellular Differentiation 79