STEM CELLS A cell that has the ability to continuously divide and differentiate (develop) into various other kind(s) of cells/tissues. Stem Cell Characteristics:  Blank cells’ (unspecialized)  Capable of dividing and renewing themselves for long periods of time (proliferation and renewal)  Have the potential to give rise to specialized cell types (differentiation)  Self renewable: a cell that has the ability to continuously divide  Pluripotent: ability to develop into several different kinds of cells/tissues  Repair: ability to return function to damaged cells in the living organism

Stem cells are unique body cells. Stem cells have the ability to – divide and renew themselves – remain undifferentiated in form – develop into a variety of specialized cell types

Stem cells are classified into three types. Totipotent: growing into any other cell type Pluripotent: growing into any cell type but a totipotent cell Multipotent: growing into cells of a closely related cell family

Kinds of stem cells Embryonic stem cells: come from a five to six-day-old embryo. They have the ability to form virtually any type of cell found in the human body. Embryonic germ cells: are derived from the part of a human embryo or foetus that will ultimately produce eggs or sperm (gametes). Adult stem cells: are undifferentiated cells found among specialised or differentiated cells in a tissue or organ after birth. (Or) Stem cells found in adult organisms, for instance in bone marrow, are called adult stem cells. Based on current research they appear to have a more restricted ability to produce different cell types and to self-renew.

Scientists have recently demonstrated that stem cells, both embryonic and adult, with the right laboratory culture conditions, differentiate into specialized cells.

Embryonic stem cells Embryonic Stem Cells (ESC): received from: Embryos created in vitro fertilization Aborted embryos Source of ESC: 1. Blastocyst “ball of cells” 3-5 day old embryo Stem cells give rise to multiple specialized cell types that make up the heart, lung, skin, and other tissues 2. Human ESC were only studied since 1998 It took scientists 20 years to learn how to grow human ESC following studies with mouse ESC

How are embryonic stem cells harvested? Human ES cells are derived from 4-5 day old blastocyst Blastocyst structures include: Trophoblast: outer layer of cells that surrounds the blastocyst & forms the placenta Blastocoel: (“blastoseel”) the hollow cavity inside the blastocyst that will form body cavity Inner cell mass: a group of approx. 30 cells at one end of the blastocoel: Forms 3 germ layers that form all embryonic tissues (endoderm, mesoderm, ectoderm)

Stages of Embryogenesis

Blastocyst Diagram

Development of specialized cells

Adult stem cells Adult Stem Cells (ASC): can be received from: – Limited tissues (bone marrow, muscle, brain) Discrete populations of adult stem cells generate replacements for cells that are lost through normal wear and tear, injury or disease – Placental cord – Baby teeth Baby teeth

Continued.. Adult or somatic stem cells have unknown origin in mature tissues – Unlike embryonic stem cells, which are defined by their origin (inner cell mass of the blastocyst) Adult stem cells typically generate the cell types of the tissue in which they reside – Stem cells that reside in bone marrow give rise to RBC, WBC and platelets – Recent experiments have raised the possibility that stem cells from one tissue can give rise to other cell types This is known as PLASTICITY Ex: Blood cells becoming neurons, Liver cells stimulated to produce insulin, Hematopoietic (blood cell producing) stem cells that become heart cells

Applications Basic research – clarification of complex events that occur during human development & understanding molecular basis of cancer Molecular mechanisms for gene control Role of signals in gene expression & differentiation of the stem cell Stem cell theory of cancer Biotechnology(drug discovery & development) – stem cells can provide specific cell types to test new drugs – Safety testing of new drugs on differentiated cell lines – Screening of potential drugs Cancer cell lines are already being used to screen potential anti- tumor drugs Availability of pluripotent stem cells would allow drug testing in a wider range of cell types & to reduce animal testing

Continued.. Cell based therapies: – Regenerative therapy to treat Parkinson’s, Alzheimer’s, ALS, spinal cord injury, stroke, severe burns, heart disease, diabetes, osteoarthritis, and rheumatoid arthritis – Stem cells in gene therapy – Stem cells as vehicles after they have been genetically manipulated – Stem cells in therapeutic cloning – Stem cells in cancer

The use of stem cells offers many currently realized and potential benefits. –Stem cells are used to treat leukemia and lymphoma. –Stem cells may cure disease or replace damaged organs. –Stem cells may revolutionize the drug development process.