stem cells and the maintenance of adult tissues chapt 17 2. stem cells have great potential adult...
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Stem Cells and the Maintenance of Adult Tissues
Chapt 17 2. Stem cells have great potential
Adult stem cells
Embryonic stem cells
In early development, cells proliferate rapidly, then differentiate to form specialized cells of adult tissues
Most differentiated cells in adult animals are no longer capable of proliferation.
If cells are lost, replace by proliferation of cells derived from self-renewing stem cells.
Stem Cells,Maintenance of Adult Tissues
1. Some differentiated cells can proliferate to repair damaged tissues Fibroblasts in connective tissue proliferate in response to platelet-derived growth factor (PDGF) released at wound
Endothelial cells lining blood vessels proliferate to form new blood vessels (repair and regrowth of damaged tissue) Triggered by vascular endothelial growth factor (VEGF), from cells that lack oxygen
Fig. 17.13,14, 15
Stem Cells and the Maintenance of Adult Tissues
2. Adult Stem cells:
Less differentiated, self-renewing cells in most adult tissues.
Retain capacity to proliferate, replace differentiated cells throughout lifetime of animal.
** Divide to produce one daughter cell that remains stem cell and one that divides, differentiates
Ex. blood cells, sperm, epithelial cells skin, intestine
Fig. 17.17
Fig 17.18 Formation of blood cells
Hematopoietic (blood-forming) stem cells were the first identified (1961): • distinct types • specialized functions• Short life span• from bone marrow
Stem Cells and Maintenance of Adult Tissues
Epithelial cells that line intestines live only a few days before they die
Fig. 17.19
Stem Cells and the Maintenance of Adult Tissues
Adult stem cells potential utility in medicine.
Hematopoietic stem cell transplantation (or bone marrow transplantation) important role in treatment of cancers.
Cord blood is source of hematopoietic stem cellsEpithelial stem cells - skin grafts for burns, wounds, and ulcers.
Fig. 17.22
Embryonic Stem Cells and Therapeutic Cloning
3. Embryonic stem cells (ES)
Grow indefinitely as pure stem cell populations Pluripotency — capacity to develop into all of
different types of cells in adult tissues.
Enormous interest - basic science and clinical applications.
Distinction cloning cells versus cloning organisms
Embryonic Stem Cells and Therapeutic Cloning
ES cells first cultured from mouse embryos in 1981.Mouse ES cells important experimental tool: Can introduce altered genes into mice. Model system to study molecular basis of cell differentiation
Fig. 17.23 ES cells can differentiate: Martin Expt: neuron-like, endodermal, cartilage
Embryonic Stem Cells and Therapeutic Cloning
Mouse ES cells need growth factor LIF, to maintain undifferentiated state (leukemia inhibitory factor)
LIF signals through JAK/STAT path If LIF is removed, cells aggregate and differentiate. Different growth factors direct differentiation along specific paths
Model for future human therapeutics:Diseases like Parkinson’s, diabetes
Human ES cell lines exist
Fig. 17.24
Embryonic Stem Cells and Therapeutic Cloning
1997 Dolly the sheep cloned: Somatic cell nuclear transfer
process This cloning in mammals is
difficult and inefficient Possible therapeutic cloning
Fig. 17.25
Embryonic Stem Cells and Therapeutic Cloning
Therapeutic cloning: Nucleus from adult human cell
transferred to enucleated egg Resulting embryo cells used to
produce differentiated cells for transplantation therapy.
Bypasses problem of tissue rejection
Problems with therapeutic cloning: Low efficiency of generating embryos
by somatic cell nuclear transfer. Ethical concerns:
• Possible cloning of humans (reproductive cloning),
• destruction of embryos
Fig. 17.26 therapeutic cloning for personalized tissue transplants
Embryonic Stem Cells and Therapeutic Cloning
Induced pluripotent stem cells: Very recent procedures may overcome technical, ethical difficulties
Reprogram somatic cells to resemble embryonic stem cells.
Only 4 key transcription factorsreprogram adult mouse somatic cells
Oct4, Sox2, Klf4, c-Myc) Also adult human fibroblasts
Fig. 17.27