Outline:I. Introduction A. Definition of Stem Cell B. History and Discovery of SCsII. Therapeutic Applications of SCs A. Methods for studying Stem Cells B. Problems with cloning C. Alternatives to cloningIII. PolicyIV. Nuclear Reprogramming
Properties of Stem Cells• Self-renewal• Potency ･Totipotent: Includes fertilized zygote and first few divisions of the fertilized egg. These cells can differentiate into embryonic and extraembryonic cell types. ･Pluripotent: SC’s are the descendants of totipotent cells and can differentiate into cells derived from any of the three germ layers. ･Multipotent: SC’s 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: SC’s 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).
Where do SC come from? EmbryonicFetal Stem Cells Berashis Adult
When do SC arise?
Major Types of Stem Cells Embryonic Stem Adult Stem Cells Cells • Multipotent: cell can• Totipotent : cell can develop into a few develop into all cell cell types but not all types • Located in few• “Immortal”: can self- organs or may be renew indefinitely unidentified• Plentiful • Hard to find
Embryonic Stem cells Embryos areformed in labs thathelp couples getpregnant. An eggand sperm fertilizea zygote and areinserted into awoman’s uterus todevelop into anembryo and then http://biodidac.bio.uottawa.ca/thumbnails/filedet.htm?File_name=HUMN150B&File_ty fetus. Life Sciences-HHMI pe=GIF Outreach. Copyright 2006 President and Fellows of Harvard College.
Embryonic Stem Cells This process creates multiple embryos that will not be used to make a baby. Many donors wish to donate these unused embryos to scientific researchFirst stages of segmentation of a mammalian ovum. Semidiagrammatic. z.p. Zonastriata. p.gl. Polar bodies. a. Two-cell stage. b. Four-cell stage. c. Eight-cell stage. instead of havingd, e. Morula stage. the lab throw them away. http://en.wikipedia.org/wiki/Polar_bodies
Embryonic Stem CellsThe embryo used inresearch is 4-5 days oldand is a microscopicball of about 150 cells.The ball as thick as ahair is called aBlastocyst and hasthree layers calledgerm layers. Eachlayer has special stemcells that makes a partof the body. Life Sciences-HHMI Outreach. Copyright 2006 President and http://en.wikipedia.org/wiki/Image:Blastocyst.svg Fellows of Harvard College.
Blastocyst:Source of Embryonic Stem Cells Blastocyst under the microscope Life Sciences-HHMI Outreach.
Germ Layers The embryo develops threegerm layers of cells called the ectoderm, mesoderm and endoderm
Embryonic Stem Cell These embryos not used in IVF will not grow into a fetus or baby because an embryo like the one in the picture needs to be implanted inside a woman’s uterus to develop into a human fetus. Fetuses and babies are not aborted for stem cell research.AuthorPhotograph by Ed Uthman, MD.PermissionPD Public domainhttp://en.wikipedia.org/wiki/Image:Tubal_Pregnancy_with_embryo.jpg. Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.
Embryonic Stem Cells Embryos can also be usedfor cloning research. Theprocess called SomaticNuclear Transfer (SNT)removes an embryo’snucleus and replaces it withanother person’s adult cellnucleus. The embryo wouldthen have the ability todevelop into a clone orgenetic copy of the nucleusdonor if the embryo wereimplanted into a woman’suterus. http://en.wikipedia.org/wiki/Image:Icsi.JPG
Dolly the Sheep was first cloned using SNT. An adult sheep body cell nucleus wasimplanted into an embryo and then implanted in a mother sheep’s uterus. http://en.wikipedia.org/wiki/Image:Dollyscotland.JPG Life Sciences-HHMI Outreach.
Adult Stem CellsAdult stem cells arecalled somatic or bodystem cells. Somepeople call these adultbecause they are foundafter an embryodevelops into a fetusand are no longer anembryonic stem cell.Not only adults haveadult stem cells! Someorgans are believed tolack stem cells andthese cells grow andreplace dead cells withmitosis. http://en.wikipedia.org/wiki/Image:Mitosis-flourescent.jp
Adult Stem Cells Adult stem cells develop into a few cell types. These multipotent cells are used in bone-marrow transplants and will develop into all the blood cells. These cells are important, but somehttp://www.ulb.ac.be/sciences/biodic/homepage2.htm red corpuscles figurel organs may not have adult stem cells and these cells can be difficult to find.
All Stem Cells Are Important• All stem cells can help scientists learn how cells regenerate or repair injured cells, tissues and organs.• Scientists need both types of stem cells for their research.• Each cell type can help inform scientists on how we develop and how some diseases affect our cells. Life Sciences-HHMI Outreach.
Stem Cell Debate Some people oppose stem cell researchbecause they believe that the 4-5 day old ballof cells is a living human being. What somedo not understand is that unused embryosare trashed regardless. Many people,religious and non-religious, believe it is betterto use these embryos for research on how tocure human diseases rather than to just trashthem without purpose. The underlying issueis the personal belief when life actuallybegins.
Misconceptions• Pregnancy, fetuses or babies are aborted or harmed in stem cell research.Fact: Fertilized Blastocysts donated from IVF labs are used and no pregnancy is aborted.• The fertilized embryos are removed from women’s bodies and used for research.Fact: The embryos are left over from IVF and are frozen and are not implanted for pregnancy.
Misconceptions • A clone is grown in a lab without an embryo or born from a mother and is the same age and personality as you, and has no belly button. Fact: a clone would need a fertilized embryo and would have to be implanted in a woman’s uterus. If you were cloned at 14, the clone would be 14 years younger than you (a baby you) and would have to have a mother to be born, so yes, it would have a belly button. Life Sciences-HHMI Outreach.http://en.wikipedia.org/wiki/Image:Femnavel.jpg
Misconceptions• If the embryos were not used in stem cell research they would have been used to make children.Fact: The embryos left over from IVF are discarded.• Men and women who donate their embryos do not know that their embryos are used for research.Fact: The embryos used in scientific research are donated with written and informed Life Sciences-HHMI Outreach.
Stem Cell ResearchSome scientists want to identify thegenes and processes used in embryodevelopment to figure out how to makenew cells in damaged or diseased cellsand organs or fix old cells byreprogramming them to be young cellsagain. Life Sciences-HHMI Outreach.
Cell-Based TherapiesScience has known for a long time that certainorganisms and organs can regenerate or re-grow themselves after being damaged or injured.For example, planaria can regenerate after beingcut up into small pieces and certain lizards canregenerate limbs and tails. Scientists want toknow “How do they do it?” and study theseanimals in the lab. Using cells to medicallyregenerate or replace dead or injured cells is anexample of a cell-based therapy.
Cell-Based Therapy• If your skin was burned in an accident, there would be layers of skin cells that die. Using stem cell techniques, scientists could take a skin cell from another area on your body or stem cell and grow new plates of skin tissue in a lab tissue culture dish to regenerate new skin cells for you. http://biodidac.bio.uottawa.ca/thumbnails/filedet.htm?File_name=HUMN164B&File_type=GIF
Future ApplicationsStem Cells may one day help scientists toregenerate cells lost in diseases like:• Repair heart muscle after a heart attack• Pancreas cells lost in diabetes• Neurons lost in Alzheimer’s• Retinal cells causing blindness• Understand the cell growths of cancers• Help organ transplantation
Therapeutic Cloning• Nuclear Transfer: Method is the same as was used to clone Dolly the sheep in February 1997
Problems with Therapeutic Cloning• Cost• Destruction of embryos• Inefficiency – 277 cells taken from Dolly’s “mother,” but only 30 became blastocysts. (13.21%)
III. Policy Issues •Current policy only allows federal funding for existing embryonic stem cell lines (21 in all), not new ones• No federal law criminalizing destruction of embryos, though some states have these laws• Proposition 71 in California – explicitly permits research using somatic cell nuclear transfer• 2008 presidential election could bring about a significant change in current policy• What’s your opinion?