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Lecture notes of 11 pages for the course Cell Biology and developmental genetics at QMUL
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RegenerationLearning objective:
1. Learn the 4 different mechanisms of regeneration + examples
2. Why mammalian and avian cannot regenerate their CNS
What is regeneration?
It is the reactivation of development in postembryonic life to restore missing tissue
Why can salamander grow back limbs but humans cannot?
There are 4 different ways by which regeneration can occur
Can have combination of different modes
1. Stem cell-mediated regeneration
- E.g. regrowth of hair
- Replacement of blood cells
- Present in humans
2. Epimorphosis
- Dedifferentiation of adult structures to form undifferentiated mass of cells that then become respecified
- E.g. regeneration of salamander limbs
- Blasteme forms
- Some definition just say that cell proliferation occurs not necessarily the formation of blastemal
- Examples given for this lecture is blastemal formation.
Blastemal = mass of cells capable of growth and regeneration into organs and body parts
- Dedifferentiate = cell or tissue undergo a reversal of differentiation and lose specialised characteristics
3. Morphallaxis
- Regeneration occurs through repatterning of existing tissue with little new growth
- E.g. hydra
- Not associated with cell proliferation
4. Compensatory regeneration
-differentiated cells divide but maintain their differentiated functions
- e.g. mammalian liver
Occurs in humans
1. Stem cell-mediated regeneration
(Embryonic) Stem cells can proliferate, creating more stem cells (self-renewal)
Stem cells can give rise to more differentiated cellular progeny by asymmetric cell divisions
Adult stem cells are populations of embryonic stem cells which have been retained
Difference between adult and embryonic stem cells
Embryonic stem cells
- Stem cells derived from undifferentiated inner mass cells of a human embryo
- Pluripotent, meaning able to grow (i.e. differentiate) into all derivatives of the 3 primary germ layers: ectoderm,
endoderm, mesoderm.
During organisms life adult stem cell continuously produce more stem cells but also cells that differentiate
Blood cells
Intestinal cells
Epidermal cells Continuously replenished
Sperm cells in males
Injury and environmental factors can cause the production of enormous number of cells
- E.g. RBC when body suffers from hypoxia
- Hypoxia = deficiency in amount of oxygen reaching tissues
, Hematopoietic stem cells are derived from 3 embryonic regions
Hematopoietic are stem cells that give rise to all other blood cells through a process of haematopoiesis. They are
derived from mesoderm and located in the red bone marrow, which is contained in the core of most bones.
HSCs from all 3 sources (yolk sac, AGM, placenta) migrate to fatal liver and at time of birth are found in the bone
marrow.
The bone marrow presents the stem cell niche
AGM= aorta-gonas-mesonephos region (lateral plate mesoderm near aorta)
Osteoblasts from the stem cell niche sends signal to HSC to maintained their stem cells throughout life
Osteoblast signal to the HSCs by activating 3 signal transduction pathway:
1. Notch
2. Wnt
3. Receptor tyrosine kinase
Osteoblast = cell secretes the substance of bone
Endosteal = vascular membrane of connective tissue that lines inner surface of bonny tissue that forms the medullary
cavity of long bones.
HSC has receptors for all the 3 signal transduction pathway
Frizzled receptor mentioned in drosophila segmentation
Notch is another vital signal transduction pathway in development and functions in neurogenesis (formation of neurons
from neural stem cells)
Receptor tyrosine kinase is important in the development of a nervous system
The 3 signalling pathways tell the HSC to maintain stem cell fate
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