Cell Differentiation

Cell Differentiation

Stem Cells: • Unspecialised cells which are capable of proliferation (repeated division via mitosis) and differentiation (development into other specialised cells) • From cells in inner cell mass (approx 30 cells) eventually all types of specialised cells differentiate (approx 200) • Although all cells have the same DNA, as stem cells proliferate, different genes activate. (differentiation) • Signals for activation may be: • Internal (genes) • External (microenvironment- chem. secreted from other cells, physical contacted with other cells and molecules in immediate environment)

Various types of stem cells: • Totipotent: potential to create any/all cell types. (found in zygote – 1st five days) • Pluripotent: Potential to create foetal cell types (but not embryonic membranes) (found in ICM) • Multipotent: Potential to create cell types which are linked by a particular function. (blood stem cell RBC, WBC etc)

Primary Germ layers (pluripotent stem cells) • Ectoderm: (closer to body stalk) • epidermis of the skin; • hair, nails, glands of skin; • lens in the eye; • receptor cells; • epithelium in mouth, nose and anal canal; • teeth enamel; • nervous system; • A. lobe of Pituitary gland, Adrenal medulla;

Primary Germ layers (pluripotent stem cells) • Mesoderm: (middle) • Skeletal, smooth & cardiac muscles; • connective tissues; • lymphoid tissues; • Endothelium of blood vessels; • epithelium of body / joint cavities; • kidney, ureter; • gonads, reproductive tracts; • adrenal cortex; • dermis of skin • Endoderm (furthest from body stalk) • Epithelium of: • A.C.; • bladder, urethra, gallbladder; • pharynx, larynx, trachea, lungs; • tonsils, thyroid, thymus glands, • Vagina.

Sources of Stem Cells: 1. Adult stem cells a. Umbilical cord blood & placental • multipotent stem cells (can be used to produce blood cells) • no harm to mother or child b. General Adult stem cells • mutlipotent stem cells 2. Embryonic • pluripotent stem cells • requires destruction of embryo

Stem Cell Research: • both therapeutic cloning and embryonic stem cell research are permitted in Australian law (as of 2006) Embryonic Stem Cell research. • Cells may be obtained by IVF and are often unused by donors • generally 4-5 days old 1. ICM is transferred to culture dish with nutrient solution 2. Cells divide (subculturing) may continue for months 3. Within 6 months 30 cells  millions • Cell may also be obtained through therapeutic cloning • Nucleus from patients cell inserted into donor egg (minus donor egg nucleus) resulting cell develops into new, identical, blastocyst.

Adult Stem cell Research. • Likely that stem cells exist in all body tissues • Scientists are trying to discover a way to reintroduce a patients own stem cells into their damaged organs rectifying disease or injury. • E.g. Umbilical cord stem cells may be used to help treat conditions such as leukaemia, anaemia and immune system diseases

Ethical Considerations (embryonic research): • Positive: • Production of replacement tissues and organs may save lives and alleviate suffering • Adult stem cell research may take many years to produce practical uses • Generally uses surplus IVF embryos which would have been destroyed anyway • Embryos used are pre-implanted and could not develop into human life unless implanted. (no difference between using morning after pill or IUD)

Ethical Considerations (embryonic research): • Negative • Stem cell research is potential but may take many years  many destroyed embryos • In future embryos may be produced solely for research  Human embryo trade • Routine destruction of embryos desensitising of value of human life • Could use adult stem cells which avoids destruction of human life

Cell Differentiation