As plants cannot escape from danger by running or taking flight, they need a special mechanism to withstand environmental stress. What empowers them to withstand harsh attacks and preserve life is the stem cell. According to Wikipedia, “plant stem cells never undergo the aging process but constantly create new specialized and unspecialized cells, and they have the potential to grow into any organ, tissue, or cell in the body.” The everlasting life is due to the hormones auxin and gibberellin. British scientists found that plant stem cells were much more sensitive to DNA damage than other cells. And once they sense damage, they trigger death of these cells.
Embryonic stem cells could be grown into more specialized cells for screening potential drugs. Cultures of cancer cells are already used for screening cancer drugs, and growing embryonic stem cells into heart, liver or nerve cells could be useful for testing drugs that affect those organs. Ideally, the human cells could be custom-made to represent the genetic diversity and traits typical of people who suffer from the disease being studied. Right now, potential drug molecules are tested first in mice and rats, but results of these animal tests do not always correlate with what happens in humans. Drugs that poison a human liver, for example, might do no harm to a rat's.
Doctors and scientists are excited about stem cells because they could help in many different areas of health and medical research. Studying stem cells may help explain how serious conditions such as birth defects and cancer come about. Stem cells may one day be used to make cells and tissues for therapy of many diseases. Examples include Parkinson's disease, Alzheimer's disease, spinal cord injury, heart disease, diabetes, and arthritis.
Cicatricial alopecia is hair loss resulting from a condition that damages the scalp and hair follicle7 (Figure 5). In addition to a bald spot, the scalp usually has an abnormal appearance. Plaques of erythema with or without scaling or pustules may be present. Conditions that can be associated with cicatricial alopecia include infections (e.g., syphilis, tuberculosis, acquired immunodeficiency syndrome, herpes zoster), autoimmune disease (discoid lupus erythematosus), sarcoidosis, scalp trauma (e.g., injuries, burns), and radiation therapy.7
Alopecia areata, also known as spot baldness, is a condition in which hair is lost from some or all areas of the body. Often it results in a few bald spots on the scalp, each about the size of a coin. Psychological stress may result. People are generally otherwise healthy. In a few, all the hair on the scalp or all body hair is lost and loss can be permanent.
The derivation of mouse ES cells was first reported in 1981,1,2 but it was not until 1998 that derivation of human ES cell lines was first reported.3 Why did it take such a long time to extend the mouse results to humans? Human ES cell lines are derived from embryos produced by in vitro fertilization (IVF), a process in which oocytes and sperm are placed together to allow fertilization to take place in a culture dish. Clinics use this method to treat certain types of infertility, and sometimes, during the course of these treatments, IVF embryos are produced that are no longer needed by the couples for producing children. Currently, there are nearly 400,000 IVF-produced embryos in frozen storage in the United States alone,4 most of which will be used to treat infertility, but some of which (~2.8%) are destined to be discarded. IVF-produced embryos that would otherwise have been discarded were the sources of the human ES cell lines derived prior to President Bush's policy decision of August 2001. These human ES cell lines are now currently eligible for federal funding. Although attempts to derive human ES cells were made as early as the 1980s, culture media for human embryos produced by IVF were suboptimal. Thus, it was difficult to culture single-cell fertilized embryos long enough to obtain healthy blastocysts for the derivation of ES cell lines. Also, species-specific differences between mice and humans meant that experience with mouse ES cells was not completely applicable to the derivation of human ES cells. In the 1990s, ES cell lines from two non-human primates, the rhesus monkey5 and the common marmoset,6 were derived, and these offered closer models for the derivation of human ES cells. Experience with non-human primate ES cell lines and improvements in culture medium for human IVF-produced embryos led rapidly to the derivation of human ES cell lines in 1998.3