Transcript Cell & Tissue Renewal and Cell Death

Cell & Tissue Renewal
Lecture 39A
BSCI 420,421,620
Dec 4, 2002
“It’s not that I’m afraid to die, I just don’t want to be there
when it happens”
- Woody Allen
1. Cell and Tissue Renewal in Animals
2. Cell death - Apoptosis
1. Cell and Tissue Renewal in Animals
Three factors control the rate that any population of cells
increases:
a. The rate that cells cycle and divide
b. The fraction of cells in the cell cycle (vs. G0 or out of cycle)
c. The rate of cell death
In multicellular animals, once the periods of embryonic and fetal
development and growth are completed, most cells withdraw
from the cell cycle.
Adult cells can be divided into three different proliferative
behaviors: (Handout)
a. Renewing (continually renewed from stem cells)
b. Expandable (reserve G0 cells can expand/ replace cells)
c. Static (Stable, differentiated populations perm out of cycle)
a. Renewing (continually renewed from stem cells)
What is a stem cell?
1. A dividing cell that usually produces one stem cell and
one cell that goes on to become terminally differentiated.
2. It is not terminally differentiated
3. [ Text: It can divide without limit] ?
How does a cell produce unequal daughter cells?
An example of environmental asymmetry:
1. Unequal contact with a
stromal cell.
(activates receptors on
one cell and not the other)
An example of division asymmetry:
2. Unequal distribution to sister cells
of cytoplasmic or nuclear proteins or
RNAs (e.g., for TFs).
Thus, one cell remains a stem cell
while a sister cell goes
forward and differentiates.
a. Renewing (continually renewed from stem cells)
E.g. Blood cells arise from multipotent stem cells
2nd e.g. intestinal epithelial cells:
b. Expandable (reserve G0 cells can expand/ replace cells)
Mitogens like PDGF stimulate the MAPK path and mitosis. E.g.
fibrolasts, endothelial cells, and smooth muscle heal a wound.
Another e.g. Satellite cells are myogenic precursor cells can
Proliferate when a skeletal muscle fiber Is killed.
These proliferating pre-myoblasts differentiate into new
Myoblasts, and fuse to form multinucleated myotubes,
which develop into new muscle fibers.
(DNA stained blue, myosin stained w fl. Anti-myosin)
c. Static (Stable, differentiated populations perm out of cycle)
E.g. Neurons, skeletal and cardiac muscle cells.
However, recent research has found BrdU-labeled cells
in the brain that can differentiate into neurons.
Similar “stem cells”
found to re-populate the
hippocampus, a region
associated with learning.