Transcript Stem Cells
Stem Cells The Stem Cell Concept A stem cell is an undifferentiated, dividing cell that gives rise to a daughter cell like itself and a daughter cell that becomes a specialized cell type. What Is a Stem Cell? Unspecialized cells Give rise to more than 225 specialized cells in the body Serve as the body’s repair system – Renew itself – Replenish other cells In Summary: Two Major Types of SC Mature Stem Cells Early Stem Cells a.k.a. Adult (includes umbilical cord & placenta) a.k.a. Embryonic; blastocystic Cells obtained from specific mature body tissues, umbilical cord, placenta Cells obtained from inner cell mass of a blastocyst Multipotent — Pluripotent — Give rise to multiple but limited cell types Flexible, give rise to any cell type in the body What Are the Sources of Mature Stem Cells? Mature Body Tissues Stem Cells are Found in the Adult, but the Most Promising Types of Stem Cells for Therapy are Embryonic Stem Cells Where Are Early Stem Cells Found? Who did it first? In 1998, U. Wisconsin research team isolates stem cells from IVF-blastocysts 5 days of development The Inner Cell Mass is the Source of Embryonic Stem Cells The embryo is destroyed by separating it into individual cells for the collection of ICM cells. How Big Is a Blastocyst? What Are the Characteristics? Early stem cells are pluripotent Retain the special ability to develop into nearly any cell type teratoma Teratoma Additional Potential Dilemmas – Therapeutic Cloning to Obtain Matched Embryonic Stem Cells Cultured mouse embryonic stem cells. Cells from any source other than you or an identical twin present the problem of rejection. If so, how can matched embryonic stem cells be obtained? A cloned embryo of a person can be made, and embryonic stem cells harvested from these clones. Some Thorny Ethical Questions Are these masses of cells a human? Is it ethical to harvest embryonic stem cells from the “extra” embryos created during in vitro fertilization? Somatic Cell Nuclear Transfer (SCNT) Sometimes referred to as “therapeutic cloning” SCNT: Asexual Reproduction No sperm involved Transfers nucleus from a mature cell into a donor egg Requires electric or chemical stimulus to begin dividing Functionally different from regular fertilized egg What Should You Know About SCNT? Purpose: – Find cures and therapies for diseases – Awaken the natural capacity for self-repair that resides in our genes Potential Results: – Patients will receive own stem cells to treat disease – No need for donor match Like transplantation, but without rejection How Would SCNT Treat Disease? What Should You Know About SCNT? No reputable scientist wants to clone human beings SCNT stem cells are alive in a Petri dish Unless implanted in uterus, you can not generate a fetus Evidence suggests that SCNT stem cells may never develop into a human even when implanted The Biotechnology of Reproductive Cloning Even under the best of circumstances, the current technology of cloning is very inefficient. Cloning provides the most direct demonstration that all cells of an individual share a common genetic blueprint. Therapeutic Cloning Is there any ethical difference between therapeutic and reproductive cloning? The Next Step? Highly unlikely. Attempts at human cloning are viewed very unfavorably in the scientific community. http://learn.genetics.utah.edu/units/clonin g/clickandclone/ Both Kinds of SCR are Needed Mature Stem Cells Early Stem Cells First isolated in 1960s First isolated in 1998 50+ years of research 9 years of research Federal Funding = >$2.7 Billion (FY02-06) Federal Funding = $132 Million (FY02-06) Results: 50+ human therapies Results: Only in animal trials; No human trials What Are the Current State Restrictions? Which States Currently Support ESCR? http://www.pbs.org/wgbh/nova/scienceno w/3209/04.html