Stem Cells

1. Stem Cells Stem cells are distinguished from other cell types by two important characteristics. First, they are unspecialized cells capable of renewing themselves through cell division, sometimes after long periods of inactivity. Second, under certain physiologic or experimental conditions, they can be induced to become tissue- or organ-specific cells with special functions. In some organs, such as the gut and bone marrow, stem cells regularly divide to repair and replace worn out or damaged tissues.

2. Types of Stem Cells • Embryonic Stem Cells - typically taken from blastocyts or from early embryos from fertility clinics. Pleuripotent. • Somatic (adult) Stem Cells - bone, reproductive organs, brain, heart: maintain and repair tissues in which they are found. • Induced Pluripotent Stem Cells (IPSC’s) - adult cells conditioned to revert to embryonic-like cells.

3. Embryonic Stem Cells Blastocyst Inner Cell Mass Trophoblast

4. Hematopoietic Tissue of Bone: an example of adult stem cells. Capable of creating several types of cells and tissues but does not provide the diversity of tissue types possible from embryonic stem cells.

5. Uses for Stem Cells • Tissue repair or replacement - for example, replacing heart tissue following a heart attack. • Research concerning developmental processes of embryos and fetuses. • Pharmaceutical (drug development and testing)

7. Identifying Embryonic Stem Cells • Must be able to grow for many generations in the lab without differentiating. • Must show specific cell surface marker proteins typical of embryonic cells. • Express specific transcription factors such as Nanog and Oct4 which are typical of early embryos. • Can form embryoid bodies.

8. Inducing Differentiation

9. Types of Adult Stem Cells • Hematopoietic stem cells give rise to all the types of blood cells: red blood cells, B lymphocytes, T lymphocytes, natural killer cells, neutrophils, basophils, eosinophils, monocytes, and macrophages. • Mesenchymal stem cells give rise to a variety of cell types: bone cells (osteocytes), cartilage cells (chondrocytes), fat cells (adipocytes), and other kinds of connective tissue cells such as those in tendons. • Neural stem cells in the brain give rise to its three major cell types: nerve cells (neurons) and two categories of non-neuronal cells—astrocytes and oligodendrocytes. • Epithelial stem cells in the lining of the digestive tract occur in deep crypts and give rise to several cell types: absorptive cells, goblet cells, paneth cells, and enteroendocrine cells. • Skin stem cells occur in the basal layer of the epidermis and at the base of hair follicles. The epidermal stem cells give rise to keratinocytes, which migrate to the surface of the skin and form a protective layer. The follicular stem cells can give rise to both the hair follicle and to the epidermis.

10. Transdifferentiation There have been a few reports of adult stem cells differentiating into tissue types other than the tissue from which they came.

11. Induced Pluripotent Stem Cells Induced pluripotent stem cells (iPSCs) are adult cells that have been genetically reprogrammed to an embryonic stem cell–like state by being forced to express genes and factors important for maintaining the defining properties of embryonic stem cells. Although these cells meet the defining criteria for pluripotent stem cells, it is not known if iPSCs and embryonic stem cells differ in clinically significant ways.