Bio 1010 Dr. Bonnie A. Bain

CHAPTER 11 Gene Regulation Part 3

Cell Signaling and Gene Regulation (p ) 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 ) 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 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 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 Modified to lack a transplant protein which causes organ rejection May some day use pig organs for human transplant Genetically modified cloned piglets

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?

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