BIO AEM BLOG :D

2008-06-04T11:49:00.000+08:00

Totipotent stem cells are produced from the fusion of an egg and sperm cell. Cells produced by the first few divisions of the fertilized egg are also totipotent. These cells can differentiate into embryonic and extraembryonic cell types.
Pluripotent stem cells are the descendants of totipotent cells and can differentiate into cells derived from any of the three germ layers.
Multipotent stem cells can produce only cells of a closely related family of cells (e.g. hematopoietic stem cells differentiate into red blood cells, white blood cells, platelets, etc.).
Unipotent cells can produce only one cell type, but have the property of self-renewal which distinguishes them from non-stem cells (e.g. muscle stem cells).
Identifying stem cells
The practical definition of a stem cell is the functional definition - the ability to regenerate tissue over a lifetime. For example, the gold standard test for a bone marrow or hematopoietic stem cell (HSC) is the ability to transplant one cell and save an individual without HSCs. In this case, a stem cell must be able to produce new blood cells and immune cells over a long term, demonstrating potency. It should also be possible to isolate stem cells from the transplanted individual, which can themselves be transplanted into another individual without HSCs, demonstrating that the stem cell was able to self-renew.
Properties of stem cells can be illustrated in vitro, using methods such as clonogenic assays, where single cells are characterized by their ability to differentiate and self-renew.[4][5] As well, stem cells can be isolated based on a distinctive set of cell surface markers. However, in vitro culture conditions can alter the behavior of cells, making it unclear whether the cells will behave in a similar manner in vivo. Considerable debate exists whether some proposed adult cell populations are truly stem cells.
The term adult stem cell refers to any cell which is found in a developed organism that has two properties: the ability to divide and create another cell like itself and also divide and create a cell more differentiated than itself. Also known as somatic (from Greek Σωματικóς, "of the body") stem cells and germline (giving rise to gametes) stem cells, they can be found in children, as well as adults.[13] Pluripotent adult stem cells are rare and generally small in number but can be found in a number of tissues including umbilical cord blood.[14] Most adult stem cells are lineage-restricted (multipotent) and are generally referred to by their tissue origin (mesenchymal stem cell, adipose-derived stem cell, endothelial stem cell, etc.).[15][16]
A great deal of adult stem cell research has focused on clarifying their capacity to divide or self-renew indefinitely and their differentiation potential.[17] In mice, pluripotent stem cells are directly generated from adult fibroblast cultures.[18]
While embryonic stem cell potential remains untested, adult stem cell treatments have been used for many years to treat successfully leukemia and related bone/blood cancers through bone marrow transplants.[19] The use of adult stem cells in research and therapy is not as controversial as embryonic stem cells, because the production of adult stem cells does not require the destruction of an embryo. Consequently, more US government funding is being provided for adult stem cell research.[20]
Pluripotent-> van give ris eto any specialized cell in the human body
- relatively abundant
- easy to identify

Multipotent- can be isolated from adult patients
- no chance of immune rejection[if the stem cells were originally taken from the same patient]

Some stem cells self renew while others form into cells with specialized function to replace the damaged cells such as skin
Hematopoietic stem cells (adult stem cells) from the bone marrow that give rise to red blood cells, white blood cells, and platelets
Mesenchymal stem cells (adult stem cells) from the bone marrow that give rise to stromal cells, fat cells, and types of bone cells
Epithelial stem cells (progenitor cells) that give rise to the various types of skin cells
Muscle satellite cells (progenitor cells) that contribute to differentiated muscle tissue

2008-06-03T09:36:00.001+08:00

Cerebral palsy is a motor disorder that typically appears in children before the age of three. The condition is generally believed to be caused by damage or trauma to the brain before it is has fully developed. “Cerebral” refers to the two halves or hemispheres of the brain. “Palsy” describes any disorder that impairs control of body movement. In cerebral palsy, the areas of the brain affected are those associated with the motor systems, which control movement. The motor areas of the brain have either been damaged or there has been a flaw in their development that disrupts the brain’s ability to control movement and posture, producing poor coordination, poor balance, or abnormal movement patterns. The difficulties of a child with cerebral palsy are not caused by problems with the muscles or nerves.

2008-06-02T19:23:00.001+08:00

Defination :
antigen that determines acceptance or rejection of a tissue graft by the immune system.

histocompatibility antigen
<immunology> A set of plasmalemmal glycoproteins on the surface of all nucleated cells that are crucial for T-cell recognition of antigens. Particularly the HLA system in humans and the H2 system in mice. They are the major antigens responsible for tissue recognition. For this reason, they are of prime importance in determining compatible organ donors for a specific transplantation procedure. Each person has unique HLA antigens. Some HLA antigens have been identified to be correlated with the presence of certain autoimmune diseases. One of these is the HLA-B27 site. Approximately 85% of patients with ankylosing spondylitis and Reiter's syndrome will have the HLA-B27 antigen present on the leukocytes.
There are two classes of histocompatibility antigens:
1. Class I, histocompatibility antigens composed of two glycosylated subunits, a heavy chain of 44 kD and beta2 microglobulin (12 kD). The heavy chain may be coded by K, D or L genes of mouse H2 and A, B or C genes of human HLA complex. Class I antigens are important in T-cell killing and are recognised in conjunction with the foreign cell surface antigens MHC restriction).
2. Class II antigens, heterodimeric histocompatibility antigens composed of alpha (32 kD) and beta (28 kD) chains. Found mostly on B lymphocytes, macrophages and accessory cells. The response of T helper cells requires that the foreign antigen is presented in conjunction with the appropriate Class II antigens. (Murine H2 Ia antigens and human HLA DR antigens are Class II).
(14 Oct 1997)