What Are Stem Cells? Stem cells are the raw material from which all of the body’s mature, differentiated cells are made. Stem cells give rise to brain cells, nerve cells, heart cells, pancreatic cells, etc.
Objectives • Differentiate between the six steps of the fertilization process • Ovulation • Fertilization • Cleavage • Morula • Blastocyst • Implantation
What’s So Special About Stem Cells? • They have the potential to replace cell tissue that has been damaged or destroyed by severe illnesses. • They can replicate themselves over and over for a very long time. • Understanding how stem cells develop into healthy and diseased cells will assist the search for cures.
Reproductive Process • Step 1 - Ovulation • Oocyte is released from the ovary and swept into the oviduct • Step 2 – Fertilzation • Sperm penetrates oocyte. • Egg + Sperm = nuclei fusion, fertilized egg (zygote)
Fertilization • As early as 12 hours after fertilization you can see the two bundles of genetic material (two pronuclei), one from each parent. • By 18-20 hours after fertilization, these pronuclei fuse, and what starts out as two cells becomes one (called a zygote)
Reproductive Process Cont. • Step 3 – Cleavage • Zygote travels down oviduct towards uterus, undergoes mitotic cell divisions • 2 cells4 cells8 cells16cells32 cells
Cleavage On day 2, the zygote has divided into two identical cells. At this stage it is called a 2-cell embryo.
Reproductive Process cont. • Step 4 – Morula • Successive divisions produce morula • Solid ball of cells that enters uterus
Reproductive Process cont. • Step 5 – Blastocyst • Morula becomes blastocyst • Hollow balls of cells with fluid filled cavity • The embryonic stem cells clump together inside the blastocyst. • The trophoblast will become the placenta. trophoblast embryonic stem cells
Reproductive Process cont. • Step 6 – Implantation • Blastocyst attaches to uterine lining
http://www.hhmi.org/biointeractive/stemcells/human_emb_dev.htmlhttp://www.hhmi.org/biointeractive/stemcells/human_emb_dev.html • http://learn.genetics.utah.edu/content/tech/cloning/clickandclone/ SCAN – Stem Cell Action Network
Objectives • Differentiate between the 3 different types of stem cells • List and explain the two sources of embryonic stem cells • Explain In-vitro fertilization procedure • Explain where leftover embryos come from • List and explain ethical debate (points of controversy) • Explain Therapeutic Cloning • Procedure • Ethical debate (points of controversy)
Different Types of Stem Cells • Totipotent • Cells in morula • <3 days old • Can give rise to any human cell type • Pluripotent • Blastocyst (inner cell mass) • Between 5-10 days old • Can produce all of the 220 cell types • Can NOT produce placenta or extra embryonic tissue • Multipotent • Adult stem cells or tissue specific cells • >10 days old • Can give rise to multiple, but a limited number of lineages
Totipotent This cell Can form the Embryo and placenta Pluripotent This cell Can just form the embryo Multi- potent Fully mature
Two Sources of Embryonic Stem Cells 1. Excess fertilized eggs from IVF (in-vitro fertilization) clinics 2. Therapeutic cloning (somatic cell nuclear transfer)
What is In vitro Fertilization? (IVF) • Vitro = Latin for “glass” • Technique used for fertility purposes • Woman given fertility medications • Trigger egg release from ovaries • Fertilized in vitro with sperm • Egg grown through blastula stage implanted into uterus • Remaining unused eggs frozen
In vitro Fertilization and stem cells • Frozen embryos thawed • Pluripotent cells (inner mass- blastula) removed and grown • Can self-renew indefinitely • Make more of themselves by constant division • Can differentiate cells into cell and tissue types of interest • Diabetes • Parkinson’s • Alzheimer's
Tens of thousands of frozen embryos are routinely destroyed when couples finish their treatment. • These surplus embryos can be used to produce stem cells. • Regenerative medical research aims to develop these cells into new, healthy tissue to heal severe illnesses. SCAN – Stem Cell Action Network
Ethical Debate • Points of Controversy • The blastula was originally created by an infertile couple wanting to have children—does the original purpose for creating the blastula matter? • Should “leftover” embryos from IVF be used in this way? How else might they be used? • Should donor have to give consent to donate their blastulas?
Therapeutic Cloning • Aka Somatic Cell Nuclear Transfer (SCNT) • Used to create stem cells that are genetic match to donor • Dolly the sheep • Somatic cell = any cell other than gametes (sex cells)
Therapeutic Cloning • Procedure • Nucleus of donated egg is removed and nucleus from a patient’s somatic cell is inserted • Electric and chemical signals stimulate growth • Behaves as newly fertilized cell • Mitotically divides zygote morula blastocyst • In center there is blastocystremovedgrown in lab • These pluripotent embryonic stem cells (ESC) are genetically identical to original somatic cell from patient
Somatic Cell Nuclear Transfer • The nucleus of a donated egg is removed and replaced with the nucleus of a mature, "somatic cell" (a skin cell, for example). • No sperm is involved in this process, and no embryo is created to be implanted in a woman’s womb. • The resulting stem cells can potentially develop into specialized cells that are useful for treating severe illnesses. SCAN – Stem Cell Action Network
Ethical Debate • Points of Controversy • Could this lead to reproductive cloning? • Should women be paid for donating eggs? • Is it better to use cells from a blastula that was never intended to become a baby?
Two Sources of Adult Stem Cells • Induced Pluripotent Stem Cells (iPS) • Umbilical Cord and Bone Marrow
Stem Cell Research Worldwide SCAN – Stem Cell Action Network