Transcript Bio 1010 Dr. Bonnie A. Bain

Bio 1010
Dr. Bonnie A. Bain
CHAPTER 11
Gene Regulation
Part 3
Cell Signaling and Gene Regulation
(p. 205-206)
Cell to cell signaling is a key mechanism in
development (egg to adult)
Cell to cell signaling also co-ordinates cell
activities in the adult organism
Figure 11.10_1
Step 1
Signaling cell secretes
a molecule (signal)
Figure 11.10_2
Step 2:
Signal molecule binds
to a specific receptor
Figure 11.10_3
Step 3:
The binding activates
a series of
relay proteins
The last relay protein
activates a
transcription factor
Figure 11.10_4
The gene is
transcribed
and translated to
produce a protein
CLONING
(p. 207-210)
Even though only certain genes are
expressed in a particular cell type
Each cell in an organism carries the entire
genome of the organism
A clone is an exact genetic copy of the
original (parent) organism
When a cell divides by mitosis, it produces
two genetically identical daughter cells
The daughter cells are clones of the parent
Figure 8.2a
Many organisms can naturally reproduce by
cloning:
Amoeba and other single-celled organisms
Most plants (example: African Violet)
Some animals (sea anemones)
Figure 8.2c
Figure 11.12
Carrot Cloning in a test tube
Figure 17.11a
Sea anemone
Can reproduce
by cloning
or
by sexual
reproduction
Extra Photo 17.11ax1
Extra Photo 17.11ax2
Most animals can't reproduce by cloning
but some of them can regenerate lost limbs
or other body parts
Examples:
Sea star (p. 123 in textbook)
Grows a new body from a single arm + a
bit of the original body
Salamander:
Can re-grow a lost limb
Regeneration requires that the cells revert
back to a de-differentiated state
then divide (by mitosis) until the limb is
replaced
and then re-differentiate once the limb is
replaced
Cell differentiation:
In the embryo, all cells are the same
As the organism grows and develops,
certain cells become specialized (nerve
cells, muscle cells, etc.)
Cell differentiation:
Once they are specialized, animal cells
tend not to de-differentiate (lose their
specialization)
Regeneration requires that the cells revert
back to a de-differentiated state and then
re-differentiate again once the limb is
replaced
Genetic Potential
Organisms which can reproduce by cloning
and those which can regenerate lost parts
retain their full genetic potential in every cell
Cells from animals which do not normally
clone or regenerate also retain their full
genetic potential
They can be cloned in the lab
Reproductive Cloning of Animals
(Nuclear Transplantation)
Frog Experiment (done in the 1950's):
Frog eggs
remove the nuclei
replace with nuclei from intestinal cells of a
tadpole
Result: the eggs develop into frogs
Nuclear Transplantation
Animal Egg
Remove its nucleus
Replace it with the nucleus from an adult
body cell (somatic cell)
Result: the egg with the adult body cell
nucleus grows into a clone of the adult
nucleus donor
Figure 11.13
Cloning by Nuclear Transplantation
This is how “Dolly” was cloned
First cloned mammal
Nuclear Transplantation
For mammals, the egg with the new nucleus
has to be implanted into a surrogate mother
in order for the embryo to develop properly
Baby is usually born by Cesarean section
rather than natural birth
Clones tend to be larger than non-clone
babies
Nuclear Transplantation
This technique has been successful with
Sheep
Cats
Cows
Pigs
Goats
Rabbits
Mice
Some endangered mammals
Figure 11.14
Genetically modified cloned piglets
Modified to lack a transplant protein which causes organ rejection
May some day use pig organs for human transplant
Cloned Kitties!
Figure 11.00a
Figure 11.1a
Cloned Gaur or Asian Ox
Figure 11.1b
Cloned Mouflon (wild European sheep)
Figure 11.1c
Cloned Banteng from Java, Indonesia
Cloning Details for the Banteng:
(Cloned in 2003)
Somatic cells from a frozen zoo-raised
Banteng which had died 23 years before
Egg cells from a cow
Surrogate mother: cow
(Cows and Bantengs are closely related)
Cloning Details for Dolly the sheep:
(Cloned in 1997)
Somatic cells: sheep udder cells
Eggs: sheep, with nuclei removed
Sheep udder cells were fused (by electric
shocks) with the de-nucleated eggs
Surrogate mother: unrelated ewes (female
sheep)
Cloning Details for Dolly the sheep:
(Cloned in 1997)
For Dolly, 277 eggs were used
29 resulted in embryos
Cloning Details for Cc (Copycat):
(Cloned in 2002)
Somatic cell: ovarian cell (not an egg)
from an adult tortoiseshell female cat
Egg cell: adult cat
Surrogate mother: cat
Cloning Details for Cc (Copycat):
(Cloned in 2002)
188 attempts to create embryos
87 cloned embryos were made
Transferred into 8 surrogate mothers
2 pregnancies were started
Only one pregnancy was successful
Other Cloning Attempts:
(Small Mammals)
Mice:
1,000 embryos yielded 2 baby mice
613 embryos yielded 5 baby mice
Rabbits:
1,852 embryos yielded 6 baby rabbits
Other Cloning Attempts:
(Big Mammals)
Pigs: 72 embryos yielded 5 baby pigs
Goats: 85 embryos yielded 3 baby goats
Cattle: 496 embryos yielded 24 baby cows
Problems with Cloning
1. For mammals, it can be very wasteful
2. Takes lots and lots of somatic cells and
eggs in order to produce 1 clone
3. Caesarean rather than natural birth
4. Many cloning attempts were
unsuccessful: Dogs, monkeys, wild cats
Problems with Cloning
5. Some clones die shortly after birth
Example: the wild ox
6. Telomeres and cell age
Telomeres and Cell Age
Many clones are older than their birth age
Dolly the sheep was cloned from a 6 year
old sheep
so Dolly was genetically 6 years old already
at birth
Telomeres and Cell Age
Some mammals, like cows, don't have this
problem
Cow clone cells are the same age
as the cow clone itself
Why? Their telomeres re-set during the
embryonic stage
What is a Telomere?
Telomeres are bits of DNA at the ends of
normal chromosomes
With each cell reproductive cycle, telomeres
shorten
Eventually they are so short that the cells
can no longer reproduce
What is a Telomere?
Telomerase:
An enzyme that lengthens telomeres after
they have been shortened, permitting
extra cell reproductions
What is a Telomere?
Telomerase is found in only a few
healthy cell lines
but it is present in most cancer cell lines
It is part of the mechanism that allows
cancer cells to reproduce indefinitely
Telomeres in Cows
In 2000,
6 healthy calf clones were produced
Donor cells were from senescent cows
Senescent cows:
Old cows, their cells had doubled as often
as they were able until their telomeres were
too short to allow further doubling
Telomeres in Cows
The cloned calves had young, rather than
old, senescent cells
Their cells were capable of as many as 90
reproductive cycles
Also, their telomeres were found to be
longer than conventionally born calves
Telomeres in other Mammals
In most other cloned mammals,
the telomeres were the same age as the
somatic cells used to produce them
This caused things like premature aging
and shortened lifespans
Will all mammal clones be like this?
Will all mammal clones be like this?
How come cattle telomeres re-set when
cloned?
What will human cells do?
Will the telomeres re-set
or
Will human clones be the age of the cell
donor?
Next:
Therapeutic Cloning and Stem Cells
Cancer
Homeotic Genes