Stem cells

What does a “stem cell” mean? Can you use it in a sentence?

Do you know how stem cell is used in treatment of different diseases?

Are stem cells used nowadays? How?

1. Read this text and compare your idea of stem cells and the one given below.

Our future hope?

Stem cells are cells found in most, if not all, multicellular organisms. They are characterized by the ability to renew themselves through mitotic cell division and differentiating into a range of specialized cell types. Research in the stem cell field grew out of findings by Canadian scientists Ernest McCulloch and James Till in the 1960s.

The two types of mammalian stem cells are: embryonic stem cells that are found in blastocysts, and adult stem cells that are found in adult tissues. In a developing embryo, stem cells can differentiate into all of the specialized embryonic tissues. In adult organisms, stem cells and progenitor cells act as a repair system for the body, replenishing specialized cells, but also maintain the normal turnover of regenerative organs, such as blood, skin or intestinal tissues. To ensure self-renewal, stem cells undergo two types of cell division. Symmetric division gives rise to two identical daughter cells both endowed with stem cell properties. Asymmetric division, on the other hand, produces only one stem cell and a progenitor cell with limited self-renewal potential. Progenitors can go through several rounds of cell division before terminally differentiating into a mature cell. It is possible that the molecular distinction between symmetric and asymmetric divisions lies in differential segregation of cell membrane proteins (such as receptors) between the daughter cells.

Stem cells can now be grown and transformed into specialized cells with characteristics consistent with cells of various tissues such as muscles or nerves through cell culture. However, their use in medical therapies has been proposed.

The classical definition of a stem cell requires that it possess two properties: Self-renewal - the ability to go through numerous cycles of cell division while maintaining the undifferentiated state.

Potency - the capacity to differentiate into specialized cell types. 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. 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.

Medical researchers believe that stem cell therapy has the potential to dramatically change the treatment of human disease. A number of adult stem cell therapies already exist, particularly bone marrow transplants that are used to treat leukemia. In the future, medical researchers anticipate being able to use technologies derived from stem cell research to treat a wider variety of diseases including cancer, Parkinson's disease, Alzheimer’s disease, spinal cord injuries, Amyotrophic lateral sclerosis and muscle damage, amongst a number of other impairments and conditions. However, there still exists a great deal of social and scientific uncertainty surrounding stem cell research, which could possibly be overcome through public debate and future research, and further educa tion of the public.

Notes

* Cancer - a disease in which cells in the body grow without control, or a serious medical condition caused by this disease.

* Alzheimer's (disease) - a disease that results in the gradual loss of memory, speech, movement, and the ability to think clearly, and that is common esp. among older people.

* Parkinson's disease - is a degenerative disorder of the central nervous system that often impairs the sufferer's motor skills, speech, and other functions.

* Amyotrophic lateral sclerosis - a progressive, usually fatal, neurodegenerative disease caused by the degeneration of motor neurons, the nerve cells in the central nervous system that control voluntary muscle movement.